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NCh2369 1 OFFICIAL CHILEAN STANDARD NCh2369.Of2003 INSTITUTO NACIONAL DE NORMALIZACION INN - CHILE Earthquake-resistant design of industrial structures and facilities CONTENTS Preface 7 1 Scope and field of application 9 2 References to standards 9 3 Terms, definitions and symbols 12 3.1 Terms and definitions 12 3.2 Symbols 14 4 Provisions of general application 17 4.1 Basic principles and hypotheses 17 4.2 Procedures for specifying the seismic action 19 4.3 Classification of structures and equipment according to their importance 20 4.4 Coordination with other standards 21 4.5 Loading combinations 21 4.6 Project and review of the seismic design 23 4.7 General provision on the application of this standard 23
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Page 1: NCh2369.Of2003 (English April 25 2005) Seismic Design of Industrial Struct and Facil

NCh2369

1

OFFICIAL CHILEAN STANDARD NCh2369.Of2003

INSTITUTO NACIONAL DE NORMALIZACION INN - CHILE

Earthquake-resistant design of industrial structures and facilities

CONTENTS Preface

7

1 Scope and field of application

9

2 References to standards

9

3 Terms, definitions and symbols

12

3.1 Terms and definitions

12

3.2 Symbols

14

4 Provisions of general application

17

4.1 Basic principles and hypotheses

17

4.2 Procedures for specifying the seismic action

19

4.3 Classification of structures and equipment according to their importance

20

4.4 Coordination with other standards

21

4.5 Loading combinations

21

4.6 Project and review of the seismic design

23

4.7 General provision on the application of this standard

23

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5 Seismic analysis

23

5.1 General provisions

24

5.2 Methods of analysis

25

5.3 Static elastic analysis

26

5.4 Dynamic elastic analysis

28

5.5 Vertical earthquake action

30

5.6 Robust and rigid equipment resting at ground level

30

5.7 Design by differential horizontal displacements

30

5.8 Special analyses

31

5.9 Structures with seismic isolation or energy dissipators

32

5.10 Other structures not specifically referred to in this standard.

34

6 Seismic deformations

47

6.1 Calculation of deformations

47

6.2 Separation between structures

48

6.3 Maximum seismic deformations

48

6.4 The P-Delta effect

49

7 Secondary elements and equipment mounted on structures

49

7.1 Scope

49

7.2 Forces for seismic design

49

7.3 Forces for anchoring design

52

7.4 Automatic shutoff systems

52

8 Special provisions for steel structures

52

8.1 Applicable standards

52

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8.2 Materials

53

8.3 Braced frames

54

8.4 Rigid frames

55

8.5 Connections

56

8.6 Anchorages

57

8.7 Horizontal bracing systems

58

9 Special provisions for concrete structures

63

9.1 Reinforced concrete structures

63

9.2 Precast concrete structures

64

9.3 Industrial bays composed of cantilever columns

67

10 Provisions for foundations

69

10.1 General design provisions

69

10.2 Shallow foundations

69

11 Specific structures

70

11.1 Industrial buildings

70

11.2 Light steel bays

70

11.3 Multi-story industrial buildings

73

11.4 Large suspended equipment

73

11.5 Piping and ducts

73

11.6 Large mobile equipment

73

11.7 Elevated tanks, process vessels and steel stacks

74

11.8 Ground supported vertical tanks

74

11.9 Rotary kilns and dryers

76

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11.10 Refractory brick structures

77

11.11 Electric equipment

77

11.12 Minor structures and equipment

77

11.13 Wood structures

77

Appendix A (normative) Typical details

79

Appendix B (normative) Design of beam to column connections in rigid steel frames

89

B.1 General considerations

89

B.2 Design of the panel zone of moment connections

89

B.3 Local bending of the column flange due to a tensile force perpendicular to it

93

B.4 Local web yielding due to compression forces perpendicular to the flange

94

B.5 Web crippling due to the compression force perpendicular to the flange

95

B.6 Compression buckling of web

96

B.7 Additional requirements for continuity stiffeners

97

B.8 Additional requirements for web reinforcing plates

98

Appendix C (informative) Commentaries

99

C.1 Scope

99

C.2 References

100

C.3 Terminology and symbols

100

C.4 Provisions for general application

100

C.5 Seismic analysis

103

C.6 Seismic deformations

112

C.7 Secondary elements and equipment mounted on structures

112

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C.8 Special provisions for steel structures

113

C.9 Special provisions for concrete structures

115

C.10 Foundations

117

C.11 Specific structures

117

C.B Design of beam-column connections in stiff steel frames

126

References

128

Figures Figure 5.1 a) Seismic zonification of Region I, II, and III

44

Figure 5.1 b) Seismic zonification of Regions IV, V, VI, VII, VIII, IX, X and Metropolitan Region

45

Figure 5.1 c) Seismic zonification of Regions XI and XII

46

Figure 5.2 ----

47

Figure 8.1 Examples of width to thickness ratios of table 8.1

62

Figure 8.2 -----

63

Figure A.1 Column base

79

Figure A.2 Roof bracing

79

Figure A.3 Detail of crane beam and columns

80

Figure A.4 External wall bracing

80

Figure A.5 Connection of column to masonry wall

81

Figure A.6 Rigid equipment inside of building

81

Figure A.7 Typical details of large suspended equipment, seismic connectors and anchor bolts

82

Figure A.8 Typical details of large mobile equipment

84

Figure A.9 Wheel rail system

84

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Figure A.10 Typical details of large tanks

85

Figure A.11 Typical rotary kiln and dryer details

86

Figure A.12 Typical details of industrial brickwork

87

Figure A.13 Typical details of minor structures and equipment

88

Figure B.1 Web reinforcing plates

91

Figure B.2 Panel zone forces

92

Figure B.3 ….

95

Figure B.4 ….

97

Figure C.1 Huachipato response spectra

108

Figure C.2 Huachipato Plant design spectra

110

Figures

118

Tables Table 5.1

Seismic zonification by municipalities of the Fourth to the Ninth Region

35

Table 5.2

Value of the maximum effective acceleration A0

39

Table 5.3

Definition of the types of foundation soil 39

Table 5.4

Value of type of soil dependent parameters 40

Table 5.5

Damping ratios

40

Table 5.6

Maximum values of the response modification factor 41

Table 5.7

Maximum values of the seismic coefficient 43

Table 7.1

Maximum values of the response modification factor of secondary elements and equipment

52

Table 8.1

Limits of the width to thickness ratio 60

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OFFICIAL CHILEAN STANDARD NCh2369.Of2003 Earthquake-resistant design of industrial structures and facilities Preface The Instituto Nacional de Normalización (INN) is the Chilean standards organization in charge of studying and preparing national technical standards. The INN is a member of the International Standards Organization (ISO) and the Pan American Technical Standards Commission (CO-PANT), and represents Chile in both organizations. The standard NCh2369 was prepared by the INN Standards Division. The following organiza-tions and persons took part in its study: Arze, Reciné y Asociados Elías Arze L.

Iván Darrigrande E. Asociación de Industriales Metalúrgicos ASIMET Rodrigo Concha P. Barrios y Montecinos Ingenieros Consultores Ramón Montecinos C. Bascuñán y Maccioni Ingenieros Civiles y Asociados Alberto Maccioni Q. CADE - IDEPE Alejandro Verdugo P. Consultores Particulares David Campuzano B.

Miguel Sandor E. IEC Ingeniería Jorge Lindenberg B. Instituto Nacional de Normalización - INN Pedro Hidalgo O. Instituto Chileno del Cemento y del Hormigón Augusto Holmberg F. Marcial Baeza S. Y Asociados Marcial Baeza S. PREANSA S.A. Magno Mery G. RCP Ingeniería Ltda.. Rodrigo Concha P. SALFA I.C.S.A. Vladimir Urzúa M. S y S Ingenieros Consultores Ltda. Rodolfo Saragoni H. Universidad de Chile Maximiliano Astroza I.

María Ofelia Moroni Y. Rodolfo Saragoni H.

Universidad Técnica Federico Santa María Patricio Bonelli C. Given the inexistence of international standards on this matter, this standard represents the state-of-the-art of Chilean seismic design, which is consistent with the practice of the country’s leading engineering enterprises. The efficiency and economy of this practice has been substantiated by the seismic behavior of locally designed structures, particularly regarding such past events as those of 1960 and 1985.

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Appendixes A and B are part of this standard. Appendix C is not part of this standard, but is issued as informative supplement. The meeting of the Board of the National Standards Institute on 29 May 2003 approved this Standard. This standard has been declared Official Standard of the Republic of Chile by Decree Nº 178, of the Ministry of Housing and Urbanism, dated 1 September 2003, and then was published in the Official Gazette of Chile on 30 September 2003.

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OFFICIAL CHILEAN STANDARD NCh2369.Of2003 Earthquake-resistant design of industrial structures and facilities 1. Scope and field of application 1.1. This standard establishes the requirements for the earthquake-resistant design of heavy

and light industrial structures and facilities. It shall be applicable to structures and to duct and pipe systems, mechanical and electrical process, equipment and their respective anchorages. The standard also shall be applied to industrial warehouse structures and to buildings structured with cantilever columns.

1.2. This standard is not applicable to such other structures as nuclear stations, electric power

generation plants and transmission lines, dams, tailings dams, bridges, tunnels, gravita-tional piers, retaining walls, underground ducts, etc.

1.3. Office buildings, cafeterias or buildings similar to those destined to dwellings can be

designed compliant to NCh433.Of96. 1.4. This standard is supplemented by Nch433.Of96 Seismic Design of Buildings. All provi-

sions of this latter standard are applicable provided they have not been specifically modi-fied.

2. References to standards The following standards contain provisions, which referenced to in the text of this standard, con-stitute requirements of this standard. At the time of the issuance of this standard, the listed edition was in force. All standards are subject to revision. It is advisable that all parties that enter agreements based on this standard research the latest editions of the following standards: NOTE: The National Standardization Institute keeps a record of all national and international standards

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NCh203 Steel for structural applications – Requirements NCh433 Seismic design of buildings. NCh1159 High strength low alloy structural steel for construction NCh1537 Structural design of buildings – permanent loads and service live

loads NCh2745 Analysis and design of buildings with seismic isolation ACI 318 Building Code Requirements for Structural Concrete, 1999 ACI 350.3 Practice for the Seismic Design of Liquid Containing Structures. AISC 1989 Specifications for Structural Steel Buildings, Allowable Stress De-

sign. AISC 1999 Seismic Provision for Structural Steel Buildings – Part 1: Structural

Steel Buildings. AISC 1999 Load and Resistance Factor Design Specifications for Structural

Steel Buildings. AISI 1996 Specification for the Design of Cold Formed Steel Structural Mem-

bers. API 620 Design and Construction of Large, Welded, Low-Pressure Storage

Tanks. API 650 Welded Steel Tanks for Oil Storage AWWA-D 100 Standard for Welded Steel Tanks for Water Storage. AWWA-D 110 Wire and Strand Wound Circular, Prestressed Concrete Water Tanks.AWWA-D 115 Circular Prestressed Concrete Water Tanks With Circumferential

Tendons. UBC 97 Uniform Building Code 1997

Seismic Design of Storage Tanks, Recommendations of a Study Group of the New Zealand National Society for Earthquake Engi-neering, 1996.

NZS 4203 General Structural Design and Design Loadings for Buildings, 1992. ASTM A6/6M-98 Specification for General Requirements for Rolled Structural Steel

Bars, Plates, Shapes, and Sheet Piling. ASTM A36/A36M-97a Specification for Carbon Structural Steel. ASTM A 242/A242M-97 Specification for High Strength Low-Alloy Structural Steel. ASTM A325-97 Specification for High-Strength Bolts for Structural Steel Joints. ASTM A490-97 Specification for Heat-Treated Steel Structural Bolts, 150 ksi Mini-

mum Tensile Strength. ASTM A500-98 Specification for Cold-Formed Welded and Seamless Carbon Steel

Structural Tubing in Rounds and Shapes. ASTM A501-98 Specification for Hot-Formed Welded and Seamless Carbon Steel

Structural Tubing. ASTM A502-93 Specification for Steel Structures Rivets. ASTM A572/A572M-97c Specification for High Strength Low Alloy Columbium-Vanadium

Structural Steel. ASTM A588/A588M-97a Specification for High Strength Low-Alloy Structural Steel with 50

ksi/345 MPa/Minimum Yield Point to 4 in. (100 mm) Thick. ASTM A 913/913M-97 Specification for High Strength Low-Alloy Steel Shapes of Structural

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Quality, Produced by Quenching and Self Tempering Process (QST). ASTM A992/A992M-96 Specification for Steel for Structural Shapes for Use in Building

Framing. ANSI/AWS A5.1-91 Specification for Carbon Steel Covered Arc Welding Electrodes. ANSI/AWS A5.5-96 Specification for Low Alloy Steel Electrodes for Shielded Metal Arc

Welding. ANSI/AWS A5.17-89 Specification for Carbon Steel Electrodes and Fluxes for Submerged-

Arc Welding. ANSI/AWS A5.18-93 Carbon Steel Electrodes and Rods for Gas Shielded Arc Welding. ANSI/AWS A5.20-95 Specification for Carbon Steel Electrodes for Flux-Cored Arc Weld-

ing. ANSI/AWS A5.23-90 Specification for Low-Alloy Steel Electrodes and Fluxes for Sub-

merged Arc Welding. ANSI/AWS A5.29-80 Specification for Low-Alloy Steel Electrodes for Flux-Cored Arc

Welding. NOTE. Those foreign standards which are deemed required may be quoted.

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3. Terms, definitions and symbols 3.1 Terms and definitions The following terms and definitions apply to this standard. They supplement the terminology of NCh433.Of1996: 3.1.1 Permanent load (CP): Action whose variation in the course of time can be ignored in

relation to its mean value or one for which the variation tends to a limit. The following actions are included under this definition: - Self-weight of structural elements and finishing. - Self-weight of stationary equipment and facilities. - Normal content of vessels, hoppers, belts, and equipment. - Weight of ducts without their accumulations or incrustations. Insulation. - Permanent pushing pressure. 3.1.2 Connection: region at which several precasted elements or one precasted element and

cast-in-place element are connected. 3.1.3 Strong connection: connection that remains elastic while the pre-determined plastic

hinge zone develops an inelastic response under severe seismic conditions. 3.1.4 Wet connection: any connection compliant to ACI 318-99 sections 21.2.6, 21.2.7 and

21.3.2.3 for joining precasted elements using cast-in-place concrete or mortar filler to fill the joint space.

3.1.5 Dry connection: connection between precasted elements that does not qualify as wet

connection. 3.1.6 Process engineer: engineer in charge of the production processes, general arrangement of

equipment and structures as well as of the industrial operating processes. 3.1.7 Braced frame: structural system with diagonal elements; its elements –beams, columns

and braces– mainly act under axial forces. 3.1.8 Ductile frames with non connected non-structural elements: the non-structural ele-

ments are separated from the frame columns by a space that is larger than or equal to the value dmax defined in section 6.3.

3.1.9 Ductile frames with connected non-structural elements: These are frames in which the

non-structural elements are separated from the frame columns by a space that is smaller than the value dmax defined in section 6.3. In this case, the non-structural elements shall be

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incorporated into the structural model preventing the shear failure at the beam-column joints.

3.1.10 Rigid frame: Structural system in which the beam-column joints are capable of transmit-

ting bending moment. Its lateral stability on its plane depends on the flexural stiffness of its components.

3.1.11 Fundamental vibration period: Natural period with greater equivalent translational

mass in the direction of analysis. 3.1.12 Professional specialist: Professional of renowned structural engineering expertise legally

authorized to work in Chile and with a record of at least 5-year proven experience in earthquake-resistant design.

3.1.13 Seismic hazard: Likelihood of a certain seismic event of occurring within a determined

zone and a predetermined time interval. 3.1.14 Service Live loads (SC): Static actions, variable in time, which are determined by the

function and the use of the building and the facilities it contains. They present frequent or continuous non-ignorable variations of their mean value.

According to this definition, the following items must be included under this concept:

- Uniform loads that correspond to the use of floors and platforms considering the

normal transit of persons, vehicles, minor movable equipment and the pileup of ma-terials.

- Dust incrustation and accumulation in ducts, equipment and structures. - Crane hoist loads - Non-permanent water or earth pressures - Inner pressure of containers. - Belt loads and similar.

3.1.15 Special operating live loads (SO): Dynamic actions that arise from the normal use of

facilities. According to the foregoing definition, the loads to be included are:

- Impact and dynamic loads in general, even when they are modeled as equivalent static actions.

- Braking. - Actions that arise from moving liquids or gases, as for instance: the water hammer.

3.1.16 Accidental operating loads (SA): Actions due to operational phenomena, which only

occur occasionally in the course of the normal use of the facilities.

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According to the foregoing definition, to be included are:

- Extreme impacts and explosions - Short-circuit loads - Loads due to the overfilling of tanks and hoppers

3.2 Symbols The symbols used in this standard have the following meaning:

A0 = effective maximum ground acceleration;

Ak = weighting factor for the level k associated weight;

C = seismic coefficient for horizontal seismic action;

Cij = coupling coefficient among modes i and j;

Cmax = maximum value of the seismic coefficient;

CV = seismic coefficient for the vertical earthquake action;

CP = permanent loads;

D = Outside diameter of circular section; diameter of process tank or vessel;

E = modulus of elasticity;

Fa = allowable compression stress;

Fk = horizontal force applied at level k;

Fp = horizontal seismic force for the design of a secondary element or equipment;

Fv = Vertical seismic force; Fy = Yield stress;

Fyf = Specified yield stress of the flange of the metal shape;

H = Highest level height over the base level; total height of the

building above the base level; height of the supports of a bridge or walkway;

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I = Coefficient relative to the importance, use and failure risk of a

structure or equipment;

K = Coefficient of buckling length

Kp = Dynamic amplification factor for the design of a secondary ele-ment or equipment

L = Length of an element, span of bridge or walkway

P = Total weight of building or structure over the base level

Pk = Seismic weight associated to level k;

Pp = Weight of a secondary element or equipment;

Qo = Base shear of the building or structure;

Qp = Base shear of secondary element or equipment;

Qmin = Minimum value of the base shear;

R = modification factor of the structural response;

R1 = modification factor of the structural response as defined under 6.1;

Rp = modification factor of the structural response of a secondary ele-ment or equipment;

S = Value resulting from spectral modal superposition; minimal sup-port length; separation between structures;

Sa = Spectral design acceleration for horizontal seismic action;

Sa,v = Spectral design acceleration for vertical earthquake action;

Se = Bending moment, shear or axial force in the connection associ-ated to the development of probable strength (Spr) at the prede-termined critical sections of the structure, based on the inelastic-ity controlling mechanism;

Si = Maximum value of the i-mode contribution with its sign;

SA = Accidental operating live load;

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SC = Service live load;

SO = Special operating live load;

Ti = Vibration period of the i-mode;

T’ = Soil type dependent parameter;

T* = Fundamental vibration period in the direction of the seismic analysis;

Zk = Level k height above the base level;

a = Live load reduction factor;

ap = Acceleration at the support level of an element or equipmen;

ak = Acceleration at level k of a structure;

b = Live load amplification or magnification factor; half of the flange width in rolled or welded T, double T or TL shapes; nominal flange width of rolled channel and angle shapes; distance from the free flange edge to the bend initiation of cold formed sections; distance between the interior flange bends of bended Z, CA and Ω shapes; distance from the free edge to the first connector line or weld, or width between plate connector lines or welds;

bf = Flange width

d = Horizontal seismic deformation; total height of rolled and welded T shapes;

dd = Horizontal seismic deformation, calculated considering reduced earthquake loads by factor R;

maxdd = Maximum allowable value of dd;

di = Maximum horizontal seismic displacement of structure i;

do = Deformation due to non-earthquake service loads;

e = Flange thickness of a metal section; thickness of tank shell, stack or process vessel;

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g = Gravity acceleration;

h = Free distance between the flanges of welded shapes; free distance between flanges minus filet dimension of rolled sections; dis-tance between the nearest connectors in bolted shapes; distance in web between the initial points of the fold curves in cold formed sections; structure height at a certain level above the base level; height between two points of a structure located on the same ver-tical;

k = Factor that affects the limitation of the width to thickness ratio of double T, T and channel shapes;

n = Parameter determined by the type of soil; number of levels; r = Radius of gyration; ratio between the periods associated to two

vibration modes;

t = Flange thickness of a metal shape;

tw = Web thickness of a metal shape;

ξ = Damping ratio;

Фb = Coefficient of strength reduction as defined in AISC – LRFD;

λr = Limit of the width to thickness ratio to prevent local buckling;

λp = Limit of the width to thickness ratio to enable complete plastifi-cation of the section.

4. Provisions of general application 4.1. Basic principles and hypotheses 4.1.1. The design provisions of this standard to be applied jointly with those of each material-

specific provisions are set forth for meeting the following objectives: a Protection of life in industry

a.1 To prevent the collapse of structures in the event of severe over-design earth-quakes.

a.2 To prevent fire, explosions or emission of toxic gases and liquids.

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a.3 For environmental protection.

a.4 To assure the operability of seismic emergency exits during the seismic emer-gency.

b Continuity of operation in industry

b.1 Non-interruption of essential processes and services.

b.2 To prevent or minimize the standstill of operations.

b.3 To enable the inspection and repair of damaged elements.

4.1.2. In general terms, it is accepted that seismic analyses are based on the utilization of linear models of the structures; however, the design of resistant elements shall comply with the corresponding material-specific method, which may be by allowable stresses or ultimate loads.

4.1.3. For fulfilling the objectives of 4.1.1, a.1) the structures shall have an ample reserve of

strength and/or be capable of absorbing large quantities of energy, beyond the elastic range, prior to failure. To this end, the global structural system shall meet the following requirements:

a) To ensure the ductile behavior of the resistant elements and their connections in or-der to prevent instability or fragile failure or else to ensure their elastic behavior.

b) Provide more than one earthquake-resistant line for the earthquake actions. Earth-

quake-resistant systems shall be redundant and hyperstatic. The only exception to this provision is the explicit approval of the professional specialist defined under 3.1.12.

c) Use simple and clearly identifiable systems for the transmission of the earthquake

forces to the foundations, avoiding structures of high asymmetry and complexity.

To fulfill the objectives regarding the continuity of industrial operations and those of foregoing paragraphs a.2) and a.3), all structures, equipment, and their anchorage sys-tems shall be designed so that during severe over design earthquakes, they meet the fol-lowing requirements in addition to those set forth under a), b) and c): d) To limit the non-linear incursions, if they imply jeopardizing operational continuance

or rescue operations.

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e) Damages must occur at visible and accessible sites.

f) All emergency and control equipment, whose operation shall be guaranteed during emergencies, shall be duly certified in conformance with international standards and the approval of the process engineers and professional specialist.

4.1.4. The achievement of ductility during the cyclic behavior of the earthquake-resistant struc-

ture in accordance with 4.1.3.a.) requires the meeting of the provisions set forth under clauses 8, 9 and those in Appendix B.

4.1.5. The professional specialists and process engineers as defined in 3.1.12 and 3.1.6 shall

determine in each project the seismic design conditions of every structure, equipment and their anchorages, so as to meet the objectives set forth under 4.1.1. In particular, for each structure and equipment its seismic classification, methods of analysis, criteria, relevant parameters and illustrative drawings shall be displayed. This data shall be set on record in the project specifications. The seismic design of equipment may be made by the equip-ment manufacturer’s engineers, however the approval shall be done by the professional specialist defined under 4.6.2.

4.1.6. Location

The location of an industry shall be determined considering the hazards of earthquake-related phenomena, such as topographic amplifications, tsunamis, displacements gener-ated by soil faults and soil sliding, liquefaction and densification. To this end, in addition to complying with the provisions 4.2 of the Chilean standard NCh433.Of96, it is impera-tive that specialists undertake the corresponding geological, topographic, tsunami, and geotechnical studies.

4.2. Procedures for specifying the seismic action

The seismic actions can be specified according to one the following procedures:

a) by way of horizontal and vertical earthquake coefficients applied to the weight of the various components in which the system has been divided for analysis purpose, according to provisions 5.3, 5.5 and 5.6.

b) by way of response spectra of single-degree-of-freedom linear systems for the hori-

zontal and vertical motion of the foundation soil, according to 5.4 and 5.5.

c) by assigning descriptive values to ground movements, such as horizontal or vertical peak acceleration, velocity and displacement of the soil, in horizontal and vertical direction, or similar ones, according to 5.8.1.

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d) by real or synthetic accelerograms, duly formulated for the horizontal and vertical movements of the foundation soil, as defined in 5.8.2.

The application of the alternatives a) and b) requires the meeting of the provisions on seismic zonification of the national territory (Figure 5.1 and Table 5.1), stipulated under 4.1 of the Chilean standard NCh433.Of96 and under 4.2 of this latter standard on the ef-fects of the foundation soil (Table 5.3) and the topography on the characteristics of the seismic motion. The utilization of alternatives c) and d) shall be consistent with the results of the studies on seismic hazard, which consider the regional and local seismicity, geological, geotech-nical and topographic conditions, as well as the direct and indirect consequences of struc-ture and equipment failures. In any case, the provisions under 5.8.1 and 5.8.2 are manda-tory. Suspected near-field effects require a special analysis that takes them into account.

4.3. Classification of structures and equipment according to their importance 4.3.1. Classification

For appropriate application of this standard, structures and equipment are classified ac-cording to their importance as follows: - Category C1. Critical structures and equipment based on any one of the following

reasons:

a) Vital, must be kept in operation so to control fire, explosion and ecological damage, render health and first help services.

b) Dangerous, if their failure implies hazard of fire, explosion or air and water poisoning.

c) Essential, if their failure generates protracted standstills and serious production losses.

- Category C2. Normal structures and equipment, which may be affected by normal easily repairable failures, which do not cause protracted standstills or important production losses or hazard to other category C1 structures.

- Category C3. Minor or provisional structures and equipment, whose seismic failure

does not cause protracted standstills nor exposes to hazard other category C1 and C2 structures.

4.3.2. Importance coefficient

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The importance coefficient I for each category has the following values:

C1I = 1.20 C2I = 1.00 C3I = 0.80

4.4. Coordination with other standards 4.4.1. Chilean standards

The provisions of this standard shall be applied jointly with other material-specific load or design standards as defined in 5.3 of NCh433.Of96.

4.4.2. Foreign standards

In case of loads or materials not included under 5.2 and 5.3 of standard NCh433.Of96, in-ternationally accepted standards or criteria shall be used provided they are accepted by the professional specialist who approves the project (see 4.6.2).

In any event, these standards and criteria shall meet the principles and basic hypotheses set forth under 4.1 of this standard.

4.5. Loading combinations

The combination of earthquake loads with permanent loads and the various types of live loads shall be done by using the following rules of superposition:

a) When the allowable stress method is used in design , then

i) CP + aSC + SO*) + SA*) ± Horizontal Earthquake + Vertical Earthquake**)

*) Loads SO and SA are combined with seism only in case of the verification of one of the two following conditions for them:

i) Action SA is derived from the seismic occurrence. In this case it shall be considered with its sign.

ii) It is normally expected that the load is acting when a seism starts and goes on without in-terruption, or does not stop during the seism due to its action

If the seism generates such an effect that necessarily interrupts the actions SO or SA at the beginning of the basal accelerations, this action shall not be considered.

**) The vertical earthquake only is considered in the cases detailed under 5.1.1; its magnitude shall be determined according to 5.5.

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ii) CP + SA*) ± Horizontal Earthquake ± Vertical Earthquake**) The allowable stresses in these combinations can be increased by 33.3%.

b) When the ultimate load design method is applied, then

i) 1.2 CP + aSC + SO*) + SA*) ± b Horizontal Earthquake ± b Vertical Earthquake**)

ii) 0.9 CP + SA*) ± b Horizontal Earthquake ± 0.3 Vertical Earthquake**)

Where

a = Factor that affects live load SC determined without considering any type of re-duction. It should be equal to 1.0, except in case the process engineer author-izes a reduction of the previous value. Such reduction shall take into account the probability of simultaneous occurrence of live load with the level of the earthquake action determined by this standard. In any case, the value of “a” will at least be equal to:

TYPE OF AREA OR ELEMENT

a

Warehouses and main storage areas with low turnover

0.50

Areas of normal use, operating platforms

0.25

Diagonals supporting vertical loads

1.00

Maintenance walkways and roofs 0

b = Amplification factor of the earthquake loads as determined according to the methods of material-specific analyses in current use. It adopts the following values:

Steel structures or equipment b = 1.1

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Concrete structures or equipment b = 1.4

In the combinations i) detailed under a) and b) above, the + or – signs of the vertical earthquake shall be applied so that to obtain an effect that results in its addition to that of the loads CP and SC. In the combinations ii) shown under a) and b), the signs + or – of the vertical earthquake shall be applied so that to obtain the inverse effect, namely, the re-duction of the effect of the loads CP and SC.

The earthquake action is an eventual load that shall not be combined with other eventual loads. Special locations in mountainous and high zones, where normally wind and snow may occur in great magnitudes and duration, require special studies for determining the values of these likely coincident loads with the design earthquake.

If deemed that several content levels of vessels, pipes or tanks ought to be considered, the number of these combinations grows for covering the different situations.

4.6. Project and review of the seismic design 4.6.1. The original seismic design shall be carried out by professional specialists (see 3.1.12).

The only exception to this rule is equipment designed by foreign manufacturers. 4.6.2. The seismic design of all structures, equipment and anchorage, whichever their origin,

shall be approved by professional specialists different from their designers. 4.6.3. Drawings and calculation records shall at least contain the data set forth under 5.11 of

NCh433.Of96. The drawings and calculation records shall be signed by the original de-sign engineer referred in 4.6.1 and the professional specialist referred in 4.6.2.

The only exception are structures and equipment of category C3, which only require the presentation of the drawings signed by the original design engineer, including dimensions and materials of the resistant elements, their weight, center of gravity and anchorage de-tails.

4.6.4. The review and approval of the seismic design does not release original design engineers

from their total responsibility of fulfillment with the standards and specifications. 4.7. General provision on the application of this standard

If the type of structure is expressly stated in this standard, all corresponding design provi-sions must be used. In case the structure may be associated with various classifications that imply different design provisions, the strictest one shall be used.

5. Seismic analysis

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5.1. General Provisions 5.1.1. Direction of earthquake action

Structures shall be analyzed considering the earthquake loads at least in two horizontal, approximately perpendicular directions.

The effect of vertical earthquake accelerations shall be considered in the following cases:

a) hanging bars of suspended equipment and their supporting elements and beams of

rolled, welded or bent plate steel, with or without concrete slab as composite beam, located within the seismic zone 3, where permanent loads represent over 75% of the total load.

b) Structures and elements of prestressed concrete (pretension and post tension cable). c) Foundations and elements for anchorage and support of structures and equipment. d) Any other structure or element in which the variation of the vertical earthquake action

significantly affects its detailing, as for instance, cantilever structures and elements. e) Structures with seismic isolation sensitive to the vertical effects.

5.1.2. Combination of the effects of the horizontal components of the earthquake action.

In general the design of earthquake-resistant elements does not require that the effects of both horizontal seismic components be combined. It will be assumed that said effects are not concurrent and in consequence, the elements may be designed considering that the seism acts along each direction of analysis considered separately.

The exceptions to this simplifying rule are structures which present notorious torsional ir-regularities or have rigid frames in both directions with common columns on two inter-secting resistant lines. In these cases, the elements shall be designed based on the stresses that result from considering 100% of the earthquake acting in one direction plus the stresses which result from considering 30% of the earthquake that act in orthogonal direc-tion with respect to the previous one, and vice-versa. The largest stresses resulting from the aforementioned combinations shall be considered.

5.1.3. Seismic mass for the structural model

When calculating the horizontal inertial forces induced by an earthquake, the operating live loads may be reduced in accordance with the likelihood of its simultaneous occur-rence with the design earthquake.

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Irrespective of the previous provision, service live loads may be reduced by multiplying them by the following coefficients:

- Roofs, platforms, walkways for operation as well as for maintenance purposes

: 0

- Storage warehouses, file rooms and similar. : 0.5

The determination of the effects of vertical earthquake components in the cases detailed under 5.1.1 shall not consider any reduction of the vertical loads, except those detailed in NCh1537 for live loads.

5.2. Methods of analysis 5.2.1. General

Normally the seismic analyses shall be carried out using linear methods, for seismic ac-tions as defined under 4.2.a) or 4.2.b) or 4.2.c). In special cases, the analysis may be based on a non-linear response to a seismic action, as defined in 4.2.d).

5.2.2. Linear methods

Three procedures may be used:

a) Static analyses or analysis of equivalent static forces, which can only be applied to structures of up to 20 m height, provided their seismic response might be assimilated to a single-degree-of-freedom system.

b) Modal spectral analysis, which is applicable to any type of structure.

c) Special methods for structures featuring elastic behavior, as detailed under 5.8.

5.2.3. Non-linear methods

Non-linear methods of analysis correspond to the special methods of analysis detailed un-der 5.8, which meet the conditions of the time-history analysis as defined in 5.8.2. In conformance with the provisions 4.1 of this standard, non-linear incursion shall be moderate so to guarantee the continuity of industrial operations. The non-linear model must appropriately model the resistant capacity and the behavior of the structural elements, backed up by specific laboratory test carried out with this purpose or by normally accepted experimental studies.

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The ductility demand shall not exceed the established limit in accordance with the allow-able damage. In no element section shall surpass 2/3 of the available local ductility. The calculated maximum non-linear displacements shall not be reduced and shall conform to the limits established under 6.3. The non-linear model may incorporate the dynamic soil-structure interaction, however its influence shall be limited up to 75% of the results obtained from the same non-linear model but with rigid base.

5.3. Static elastic analysis 5.3.1. Mathematical model of the structure 5.3.1.1. The mathematical model of the structure shall be capable of appropriately represent the

load transmission from the points of application toward the supports. To that end, at least to be included are all elements of the earthquake-resistant system, the stiffness and strength of all elements that are relevant in the distribution of forces, and the correct spatial placement of masses.

5.3.1.2. In general, a three-dimensional model shall be used, excepting cases in which the be-

havior can be forecasted with two-dimensional models. 5.3.1.3. In structures without rigid horizontal diaphragms a sufficient number of nodal degrees

of freedom associated to translational masses shall be defined. If necessary, the rota-tional masses shall also be considered.

5.3.1.4. In structures with rigid horizontal diaphragms a model with three degrees of freedom

per story may be used. 5.3.1.5. In structures that support equipment, which influences the response, the mathematical

model shall consider the equipment/structure system. 5.3.1.6. In case of large suspended equipment, the mathematical model must include the suspen-

sion and interconnection devices between the equipment and the supporting structure. 5.3.1.7. If the soil characteristics or type of foundation require that the effect of soil-structure

interaction be considered, decoupled springs may be used for translational and rotational movement.

5.3.1.8. The effects of natural torsion and of accidental torsion can only be considered at levels

with rigid diaphragms. The effect of accidental torsion can be included by considering the possible variations of the distribution of self-weights and live loads. In case that no previous information is available to carry out the aforementioned, the requirement set forth under 6.2.8 in NCh433.Of96 shall be used.

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5.3.2. Horizontal base shear

The horizontal base shear shall be calculated according to the following expression: Qo = CIP

(5-1)

where Qo = base shear;

C = Seismic coefficient as defined in 5.3.3;

I = Coefficient of importance as defined in 4.3.2;

P = Total weight of the building above the base level, calculated as required under 5.1.3. To this aim, base level is the plane that separates the foundation from the structure, except indication in contrary of the professional specialist.

5.3.3. The seismic coefficient is determined from: 4.0

*

'0 05,075.2

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛=

ξ

n

TT

gRAC

(5-2)

where

Ao = Maximum effective acceleration as defined in Table 5.2 according to the seismic zonification of Figure 5.1 and Table 5.1;

T’, n = Parameters relative to the foundation soil, to be de-termined according to Tables 5.3 and 5.4;

T* = Fundamental period of vibration in the direction of the analysis;

R = Response modification factor as defined in Table 5.6;

ξ = Damping ratio as established on Table 5.5. 5.3.3.1. C need not be higher than the value specified in Table 5.7.

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5.3.3.2. C in no case shall be lower than 0.25 Ao/g. 5.3.4. Fundamental vibration period

The fundamental vibration period T* shall be calculated by a well-founded theoretic or empiric procedure.

5.3.5. Distribution along height

Seismic forces shall be distributed along height according to the following expression:

Fk = ojj

nkk QPA

PA

(5-3)

Ak = HZ

1H

Z1 k1k −−− −

(5-4)

where

Fk = Horizontal seismic force at level k ;

Pk, Pj = Seismic weight at levels k and j ;

Ak = Parameter at level k (k = 1 is the lower level);

n = Number of levels;

Qo = Base shear;

Zk, Zk-1 = Height above the base of k and k–1 levels;

H = Highest height levels above the base level; 5.4. Dynamic elastic analysis 5.4.1. Mathematical model of the structure

Provisions 5.3.1.1 to 5.3.1.7 of the static elastic analysis shall be used. 5.4.2. Design spectrum

The modal spectral analysis shall conform to the following design spectrum:

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Sa = 4.0

05,0'75.2⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛

ξ

no

TT

RIA (5-5)

where

T = Vibration period of the considered mode.

However, the value of Sa shall not be higher than ICmax · g, where Cmax shall be deter-mined according to Table 5.7.

5.4.3. Number of modes

The analysis shall include a sufficient number of vibration modes for the sum of equiva-lent masses in each analysis direction is equal to or higher than 90% of the total mass.

5.4.4. Mode superposition

Earthquake loads and deformations shall be calculated by superposing the maximum mo-dal values by means of the Complete Quadratic Superposition method according to the following formulas:

jiijji SSCS ΣΣ= (5-6)

Cij = )r1(r4)r1)(r1(

r822

5.12

+ξ+−+ξ

r = jT

Ti

(5-7)

where

S = Modal combination;

Si , Sj = Maximum values of mode contributions i and j ;

ξ = Damping ratio as defined in Table 5.5;

Ti , Tj = Period of modes i and j. 5.4.5. Minimum base shear

If the base shear Qmin is lower than the following value:

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Qmin = 0.25 I gAo P

(5-8)

for design purposes all deformations and internal forces shall be multiplied by the quo-tient Qmin/ Qo.

5.4.6. Accidental torsion

The effect of accidental torsion shall be considered only in levels with rigid diaphragm. In such cases, this effect can be included considering the possible variations of self-weight and live load distribution. In absence of background data for doing so, the provi-sion 6.3.4 of the Chilean standard NCh433.Of96 shall be used.

5.5. Vertical earthquake action 5.5.1. The vertical earthquake action may be considered as static in the following way:

a) In the cases detailed under 5.1.1. a) and 5.1.1. b) an even vertical earthquake coeffi-cient equal to Ao/g shall be applied on all elements. Therefore the vertical earthquake force must be Fv = ± (Ao/g) IP, where P is the sum of permanent loads and live loads.

b) For the cases considered under 5.1.1. c) and 5.1.1. d) the seismic coefficient shall be

2/3Aog.

c) For the cases considered under 5.1.1.e) the procedure detailed under 5.9 shall be ap-plied.

5.5.2. Alternatively a vertical dynamic analysis may be carried out with the acceleration spec-

trum of expression (5-5) for R = 3 and ξ = 0.03. In this case, the spectral ordinate does not require to be higher than IAo. Any damping ratio in excess of 0.03 shall be specifically justified.

5.6. Robust and rigid equipment resting at ground level

This provision refers to equipment whose self fundamental period is smaller or equal to 0.06 s, including the effect of its connecting system to the foundation. These equipments can be designed by static analysis with a horizontal seismic coefficient of 0.7 Ao/g and a vertical earthquake coefficient of 0.5 Ao/g.

5.7. Design by differential horizontal displacements

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For bridges or walkways that connect buildings, towers or other equipments, horizontal supports shall be provided that enable the actual seismic displacement between structures or equipment indicated in 6.2. In no case the support length shall be smaller than S, where:

S [cm] = 20 + 0.2 L + 0.5 H; L ≤ 60 m (5-9)

where

S = Minimum length of the support (see Figure 5.2)

L = Bridge or walkway span in meters between supports;

H = Height in meters of bridge or walkway supports over the foundation seal of the highest structure or equipment.

5.8. Special analyses 5.8.1. Spectral analyses 5.8.1.1. Special spectra may be developed for a specific project, such that they consider the

characteristics and importance of the structures to be built, the geotechnical conditions of the site, the distance from seismogenic sources, their characteristics, as well as the local amplification or reduction factors of the ground movement intensity in terms of site topography, the eventual effects of the wave directionality or subsoil configuration and type.

Toward this aim, a series of parameters can be determined, such as the maximum values of acceleration, velocity and displacement of the soil, and with these to configure spe-cial spectra for the viscous damping levels of Table 5.5 or for determining others, which enable similar formulations to that presented in NCh433.Of96.

5.8.1.2. For design purposes, the determination of the maximum acceleration, velocity and dis-

placements values shall take into account historical or deterministic data, which can be applied or related to the site under study. These can be supplemented with the probabil-istic values obtained from seismic risk analyses, which consider a 100-year return pe-riod. The attenuation formulas used in risk analyses shall correspond to the anticipated acceleration, velocity and displacement values, belonging to the characteristics of the seismogenic sources considered in the study.

5.8.1.3. The base shear obtained from the spectrum defined by means of this special analysis,

shall not be smaller than 75%; nor require to be larger than 125% of those resulting from the methods described under 5.4.

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5.8.2. Time-history analysis 5.8.2.1. For the time-history analyses at least three actual records shall be used, which must be

representative of the considered seismogenic zones. This data must be escalated so that the resulting spectrum from combining the spectra of each record by means of the square root of the average of the squares of the escalated individual values, is not lower than the design spectrum (5.8.1) at any point of the frequency range of interest.

5.8.2.2. Alternatively, a synthetic record may be used, whose spectrum yields larger values than

the one defined under 5.8.1, for the whole frequency range of interest. 5.8.2.3. When three different records are used, the design shall adopt the maximum values of the

parameter of interest, obtained from applying each one of them. Under this definition the meaning of parameter of interest is the action, axial force, shear, bending moment or the deformation obtained for each single element or for the global structure.

5.8.2.4. In linear time-history analyses, the resulting forces on the elements can be divided by

the R factors detailed in Table 5.6, provided the calculated displacements are compati-ble with the limits imposed in 6.3.

5.8.2.5. Time-history analyses shall consider at each time the movements in only one of the

main directions of the structure, simultaneously acting with the vertical excitation. 5.8.2.6. In time-history analyses, the damping shall be taken from Table 5.5 and the duration of

the record must be equal to or higher than 120 s, unless a seismic risk study justifies the use of a different duration.

5.8.3. Minimum base shear

If the base shear defined according to 5.8.1 or 5.8.2 is lower than

Qmin = 0.25·I PgAo (5-10)

All deformations and stresses shall be multiplied by the quotient Qmin/ Q0, except when a non-linear time-history analysis has been made.

5.9. Structures with seismic isolation or energy dissipators 5.9.1. General considerations 5.9.1.1. Seismic isolation or energy dissipation systems consist of any device that has been in-

corporated into the resistance system of a structure with the purpose of modifying its dynamic properties, be it by modifying its fundamental vibration period or by increasing

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its energy dissipation capacity or by modifying the distribution of forces with the pur-pose of enhancing its seismic response.

5.9.1.2. The structure’s lateral force resisting system and the isolation and/or energy dissipation

system shall be designed so to withstand the demand of deformation and strength pro-duced by the seismic movement, as required under 5.9, 5.8.1 and 5.8.2 of this standard.

5.9.1.3. The mathematical model of the physical structure must represent the distribution of

masses and stiffness of the structure at a suitable level for calculating the significant characteristics of the dynamic response. A three-dimensional model of the superstruc-ture that considers the vertical displacements in the isolators shall be used. The cases mentioned under 5.1.1.e) require a model that includes vertical degrees of freedom in the dynamic analysis. The damping ratios to be used shall be those corresponding to the isolation or energy dissipation systems.

5.9.1.4. The analysis and verification of the isolation and energy dissipation systems shall be

made by modal spectral analysis or time-history response or frequency response analy-sis. The modal spectral analysis can only be applied if the device or isolator is suscepti-ble of being modeled as an equivalent validated linear system.

5.9.1.5. Spectral analyses (see 5.4 and 5.8.1) or time-history response analysis (see 5.8.2) shall

consider one by one the horizontal components acting in plant in the most unfavorable direction, simultaneously with the vertical component if necessary according to 5.1.1 e).

5.9.1.6. The constitutive force-deformation relationships considered in the analysis for the se-

lected devices shall be duly founded and be backed by laboratory test. 5.9.1.7. The base shear limitations defined under 5.3.3.2 and 5.4.5 are not applicable in struc-

tures outfitted with isolation and/or energy dissipation systems. Likewise, in structures with isolators, the maximum deformation restriction defined under 6.3 is applicable only to the superstructure but not to the isolation interface.

5.9.2. Structures with seismic isolators

Seismic isolation systems shall be analyzed and designed in accordance with the provi-sions of NCh2745.

5.9.3. Structures with energy dissipators 5.9.3.1. Every structure with energy dissipation systems shall be designed using the spectra de-

scribed under 5.4 or 5.8 and subsequently be verified by three records compatible with the implicit demand level of the design spectrum, according to the methodology defined under 5.8.2.

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5.9.3.2. The seismic analysis of structures with energy dissipation systems shall be carried out by using dynamic analysis procedures that appropriately consider the constitutive force-deformation relation of the devices included in the structure.

5.9.3.3. The dissipation systems to be used in a structure shall have previously been subjected to

experimental studies, which prove a stable cyclic behavior for the device as well as pos-sible variations of its properties with temperature.

5.10. Other structures not specifically referred to in this standard.

If the base shear Q0 determined for these structures is lower than

Qmin = 0.50 I PgAo

(5-11)

All deformations and internal forces must be multiplied by the quotient Qmin/ Q0 for the purpose of the design. This provision shall not be applied to the structures, which are explicitly quoted in Table 5.6.

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Table 5.1 – Seismic zonification by municipalities of the Fourth to the Ninth Region

Region Zone 3 Zone 2 Zone 1

Andacollo Combarbalá Coquimbo Illapel La Higuera La Serena

4th Region Los Vilos Mincha

Monte Patria Ovalle Paiguano Punitaqui Río Hurtado Salamanca Vicuña

Algarrobo Calle LargaCabildo Los AndesCalera San EstebanCartagenaCasablancaCatemuConcónEl QuiscoEl TaboHijuelasLa CruzLa Ligua

5th Region LimacheLlayllayNogalesOlmuéPanquehuePapudoPetorcaPuchuncavíPutaendoQuillotaQuilpuéQuinteroRinconadaSan AntonioSan FelipeSanta MaríaSanto DomingoValparaísoVilla AlemanaViña del MarZapallar

(continues)

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Alhué BuinCuracaví Calera de TangoEl Monte CerrillosLampa Cerro NaviaMaría Pinto ColinaMelipilla ConchalíSan Pedro El BosqueTiltil Estación Central

HuechurabaIndependenciaIsla de Maipo

Metropolitan La CisternaRegion La Florida

La GranjaLa PintanaLa ReinaLas CondesLo BarnecheaLo EspejoLo PradoMaculMaipúÑuñoaPainePedro Aguirre CerdaPeñaflorPeñalolénPirqueProvidenciaPudahuelPuente AltoQuilicuraQuinta NormalRecoletaRencaSan BernardoSan JoaquínSan José de MaipoSan MiguelSan RamónSantiagoTalaganteVitacura

(continues)

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La Estrella Chépica

Las Cabras Chimbarongo Litueche Codegua Lolol Coinco

6th Region Marchigue Coltauco Navidad Doñihue

Palmilla Graneros Peralillo Machalí Paredones Malloa Peumo Mostazal Pichidegua Nancagua Pichilemu Olivar Pumanque Placilla Santa Cruz Quinta de Tilcoco Rancagua Rengo Requínoa San Fernando San Vicente de Tagua Tagua

Cauquenes Colbún Chanco Curicó Constitución Linares Curepto Longaví Empedrado Molina

7th Region Hualañé Parral Licantén Pelarco

Maule Rauco Pelluhue Retiro Pencahue Río Claro San Javier Romeral Talca Sagrada Familia Vichuquén San Clemente Teno Villa Alegre Yerbas Buenas

(continues)

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Arauco Antuco Bulnes Coihueco Cabrero El Carmen Cañete Los Angeles Chillán Mulchén Cobquecura Ñiquén Coelemu Pemuco Concepción Pinto Contulmo Quilaco Coronel Quilleco Curanilahue San Fabián Florida San Ignacio Hualqui Santa Bárbara Laja Tucapel Lebu Yungay

8th Region Los Alamos Lota Nacimiento Negrete Ninhue Penco Portezuelo Quillón Quirihue Ranquil San Carlos San Nicolás San Rosendo Santa Juana Talcahuano Tirúa Tomé Treguaco Yumbel

Angol Collipulli Curarrehue Carahue Cunco Lonquimay Galvarino Curacautín Melipeuco Los Sauces Ercilla Pucón Lumaco Freire Nueva Imperial Gorbea Purén Lautaro

9th Region Renaico Loncoche Saavedra Perquenco Teodoro Schmidt Pitrufquén Toltén Temuco Traiguén Victoria Vilcún Villarrica

(continues)

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Table 5.2 – Value of the maximum effective acceleration A0

Seismic Zone A0

1 0.20 g

2 0.30 g

3 0.40 g

Table 5.3 – Definition of the types of foundation soil. (Only to be used with Table 5.4)

Type of

soil Description

I

Rock: Natural material, with in-situ shear wave propagation speed Vs equal or higher than 900 m/s, or else with uniaxial compression strength of intact samples (without fissures) that is equal to or higher than 10Mpa and RQD equal to or higher than 50%.

II

a) Soil that features Vs equal or higher than 400 m/s in the upper 10 m, increasing with depth; or else

b) Dense gravel, with dry unit weight γd equal to or higher than 20 kN/m3, or density index ID(RD) (relative density) equal to or higher than 75%, or compacting index over 95% of the modified Proctor value, or else:

c) Dense sand of ID(RD) over 75%, or standard penetration index N over 40 (nor-malized for an effective overburden pressure of 0.10 Mpa), or compacting index over 95% of the Modified Proctor value, or else,

d) Hard cohesive soil, with undrained shear strength Su equal to or greater than 0.10 Pa (simple compression force qu equal to or greater than 0.20 Mpa) in samples without fissures.

These conditions must be met in every case, without regard to the position of the phreatic level and the minimum stratum thickness shall be 20 m. In case the thickness over the rock is under 20m, the soil shall be classified as type I.

III

a) Permanently non-saturated sand of ID(DR) between 55 and 75%, or N over 20 (with-out normalizing at 010 Mpa effective overburden pressure); or else,

b) Non-saturated gravel or sand of compacting index below 95% of the Modified Proctor Value; or else,

c) Cohesive soil with Su between 0.025 and 0.10 Mpa (qu between 0.05 and 0.20 Mpa) without regard to the phreatic level; or else,

d) Saturated sand with N between 20 and 40 (normalized at 0.10 Mpa of effective over-burden pressure).

Minimum stratum thickness: 10m. In case the stratum thickness over the rock or over type II soil is under 10m, the soil shall be classified as type II.

IV

Saturated cohesive soil with Su equal to or under 0.025 Mpa (qu equal or under 0.050 Mpa). Minimum stratum thickness: 10m. In case the stratum thickness over any of the soil types I, II or III is lower than 10m, the soil shall be classified as type III.

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Table 5.4 – Value of type of soil dependent parameters

Type of soil T’ (s) n

I 0.20 1.00

II 0.35 1.33

III 0.62 1.80

IV 1.35 1.80

Table 5.5 – Damping ratios

Resistant system

ξ

Welded steel shell; stacks; silos; hoppers; pressure vessels; process towers; piping, etc. 0.02

Bolted or riveted steel shell; 0.03

Welded steel frames with or without bracings 0.02

Steel frames with field bolted connections, with or without bracings 0.03

Reinforced concrete and masonry structures 0.05

Precast reinforced concrete, purely gravitational structures 0.05

Precast reinforced concrete structures with wet connections, connected to the non-structural elements and incorporated into the structural model

0.05

Precast reinforced concrete structures with wet connections, non-connected to the non-structural elements

0.03

Precast reinforced concrete structures with dry connections, non-connected and connected: With bolted connections and connections by means of bars embedded in filling mortar With welded connections

0.03

0.02

Other structures not included in above list or assimilable to the foregoing ones.

0.02

NOTES

1) When using an analysis that considers soil-structure interaction in which the values of the first damping mode ratio are higher than those of this table, the increase of this ratio shall not be 50% higher than the foregoing values. Values for all other modes shall be those listed in this table.

2) In case of uncertainty regarding the classification of a resistant system, apply provision 4.7.

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Table 5.6 – Maximum values of the response modification factor

Resistant system

R

1. Structures designed for remain elastic 1

2. Other structures not included nor similar to those in this list1) 2 3. Steel structures 3.1 Buildings and structures of ductile steel frames with non-connected non-

structural elements 5

3.2 Buildings and structures of ductile steel frames with connected non-structural elements that are incorporated into the structural model

3

3.3 Buildings and structures of braced frames with ductile anchorages 5 3.4 One-story industrial buildings with or without overhead traveling crane

and continuous roof bracing 5

3.5 One-story industrial buildings without overhead traveling crane, without continuous roof bracing, which are compliant to 11.1.2

3

3.6 Light steel bays that are compliant to the conditions of 11.2.1 4 3.7 Inverted pendulum structures2) 3 3.8 Earthquake-resistant isostatic structures 3 3.9 Steel plate or steel shell structures whose seismic behavior is controlled

by local buckling 3

4. Reinforced concrete structures 4.1 Building and structures of reinforced concrete ductile frames with non-

connected non-structural elements 5

4.2 Buildings and structures of reinforced concrete ductile frames with con-nected non-structural elements that are incorporated into the structural model

3

4.3 Reinforced concrete buildings and structures with shear walls 5 4.4 One-story industrial buildings with or without overhead traveling crane

and with continuous roof bracing 5

4.5 One-story industrial buildings without overhead traveling crane, without continuous roof bracing that are compliant to 11.1.2

3

Continued

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4.6 Inverted pendulum structures2) 3 4.7 Isostatic seismic structures 3 5. Precast reinforced concrete structures 5.1 Purely gravitational precast structures 5 5.2 Precast structures with wet connections, connected to the non-structural

elements and incorporated into the structural model 3

5.3 Precasted structures with wet connections, non-connected to the non-structural elements

5

5.4 Precast structures with dry connections, non-connected and connected to the non-structural elements with: Bolted connections and connections by means of bars embedded in mor-tar3)

Welded connections3)

4

4

5.5 Precast inverted pendulum structures2) or with cantilever pillars 3 5.6 Earthquake-resistant isostatic structures 3 6. Masonry structures and buildings 6.1 Reinforced block masonry with total filling of voids 4 6.2 Reinforced block masonry without total filling of voids and reinforced

block masonry with ceramic units of grid type. 3

6.3 Confined masonry 4 7. Tanks, vessels, stacks, silos and hoppers 7.1 Stacks, silos and hoppers with continuous down-to-floor shells 3 7.2 Silos, hoppers and tanks supported on columns, with or without bracing

between columns. 4

7.3 Vertical axis steel tanks with continuous down-to-floor shell 4 7.4 Vertical axis reinforced concrete tanks with continuous down-to-floor

shell 3

7.5 Tanks and conduits of composite synthetic material (FRP, GFRP, HDPE and similar materials)

3

7.6 Horizontal vessels supported on cradles with ductile anchorages 4 (continues)

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8. Towers, piping and equipment 8.1 Process towers 3 8.2 Cooling towers made of wood or plastic 4 8.3 Electric control cabinets resting on floor. 3 8.4 Steel piping except their connections 5 9. Storage racks 4 NOTES

1. Except that a study proves that an R value other than 2 can be used. Structures whose resistant system is explicitly included in this table are not assimilable to this classification.

2. Over 50% of the mass above the upper level. Only one resistant element. 3. The value R = 4 is an upper limit. If the R value is lower for the equivalent rein-

forced concrete structural system, said lower value shall be used. 4. In case of uncertainty regarding the classification of a resistant system, provision

4.7 shall be applied.

Table 5.7 – Maximum values of the seismic coefficient

Cmáx.

R ξ = 0.02 ξ = 0.03 ξ = 0.05

1 0.79 0.68 0.55 2 0.60 0.49 0.42 3 0.40 0.34 0.28 4 0.32 0.27 0.22 5 0.26 0.23 0.18

NOTE – These values are valid for seismic Zone 3. For application to zones 2 and 1, these values shall be multiplied by 0.75 and 0.50, respectively.

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Figure 5.1 a) Seismic zonification of Regions I, II and III

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Figure 5.1 b) Seismic zonification of Regions IV, V, VI, VII, VIII, IX, X and Metropolitan Region

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Figure 5.1 c) Seismic zonification of Regions XI and XII

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Figure 5.2

6. Seismic deformations 6.1 Calculation of deformations

When the analysis considers R-factor reduced earthquake loads, the deformations shall be determined as follows:

d = d0 + R1 dd (6-1)

where

d = Seismic deformation

d0 = Deformation due to non-seismic service loads

R1 = Factor resulting from multiplying the R factor derived from Table 5.6 by the quotient Q0/Qmin, provided that Q0/Qmin be lower or equal to 1.0. However, for the quotient Q0/Qmin a value under 0.5 shall not be used. If this quotient is higher than 1.0, R1 = R shall be used

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dd = Deformation calculated with R-factor reduced earth-quake loads.

If anelastic methods are used, deformation d shall be obtained directly from the analysis.

6.2 Separation between structures 6.2.1 With the purpose of preventing impacts between adjoining structures, their separation

shall be bigger than the highest of the following values:

j0i02

djj12

dii1 dd)dR()dR(S +++=

(6-2)

S = 0.002 (hi + hj)

S = 30 mm

(6-3)

where

ddi , ddj = Deformations of the structures i and j calculated as per 6.1;

R1i , R1j = response modification factors R1 used for the design of the structures i and j, and

hi , hj = height at the considered level of the structures i and j measured from their respective base levels.

6.2.2 The separation between the structure and rigid or fragile non-structural elements, whose

impact is required to be prevented, must be higher than the relative deformation between the levels where the element is located and calculated with the corresponding d values, but not less than 0.005 times of the element height.

6.3 Maximum seismic deformations

Seismic deformation must be restricted to values that do not damage piping, electric sys-tems or other elements, connected to the structure, which shall be protected. The deformations calculated by the expression (6-1) shall not exceed the following val-ues:

a) Precast concrete structures composed exclusively of an earthquake-resistant system

based on walls connected by dry connections.

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dmax

= 0.002 h (6-4)

b) Structures of masonry walls with partitions that are rigidly fastened to the structure.

dmax = 0.003 h (6-5)

c) Unbraced frames with non-connected masonry fill.

dmax = 0.0075 h (6-6)

d) Other structures

dmax = 0.015 h (6-7)

where

h = height between floors or between two points located on the same vertical.

The foregoing restrictions may be obviated if it is proved that a bigger deformation can be tolerated by the structural and non-structural elements.

6.4 The P-Delta effect

The P-Delta effect shall be considered in case the seismic deformations exceed the fol-lowing value

d = 0.015 h (6-8) 7. Secondary elements and equipment mounted on structures 7.1. Scope

Secondary elements are interior partitions and other appendages attached to the resistant structure but that are not part of it. Equipment anchored on several levels of the structure shall conform to provision 11.3.2.

7.2. Forces for seismic design

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7.2.1. According to 5.3.1.5 , in case that the secondary element or equipment is included in the modeling of the supporting structure, they shall be designed with the following horizontal earthquake loads acting in any direction:

Fp = pp

1p PR

RQ2.1< (7-1)

where

Qp = Shear load that appears at the base of the secondary element or equipment according to an analysis of the building with R-factor reduced seismic loads;

R1 = Factor defined in 6.1

Rp = Response modification factor of the secondary ele-ment or equipment according to Table 7.1;

Pp = Weight of the secondary element or equipment.

7.2.2. If it is not necessary that the equipment has to be included in the modeling of the struc-

ture, except for its mass, the design of the secondary elements and equipment may be car-ried out with the following seismic forces:

a) When the acceleration ap is known at the support level of the element or equipment as

derived from the dynamic modal analysis of the building with R-factor reduced earth-quake loads:

Fp = ppp

pp PPR

Ka0.3<

(7-2)

Where the coefficient Kp must be defined alternately by means of one of the two follow-ing procedures:

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i) Kp = 2.2 (7.3)

ii) Kp = 0.5 + 222 )3.0()1(

5.0ββ +−

(7.4)

where

β = 1 for 0.8 T* *1.1 TTp ≤≤

β = 1.25 (Tp/ T*)

for Tp < 0.8 T*

β = 0.91 (Tp/ T*)

for Tp > 1.1 T*

where

Tp = Natural period of the fundamental vibration mode of the secondary element including its anchorage system and T* is the period of the mode with the highest equivalent transla-tional mass of the structure in the direction in which the secondary element may enter in resonance. The determina-tion of β requires that the value of T* be over 0.06 s.

b) When no modal dynamic analysis of the building has been carried out:

Fp = ppp

pk PPR

Ka<

7.0 (7-5)

where ak = acceleration at level k on which the secondary ele-

ment or equipment is mounted, determined according to 7.2.4.

7.2.3. When the characteristics of the building are unknown or the level on which the secondary

element or equipment will be mounted is not known, the design can be carried out with the seismic force of the expression (7-5) using Kp = 2.2. and ak = 4 A0/g.

7.2.4. The acceleration at level k of the structure shall be determined by:

ak = ⎟⎠⎞

⎜⎝⎛ +

HZ

31gA k0 (7-6)

where A0 = maximum effective acceleration as defined under

5.3.3 ; Zk = height of level k above the base level; H = total height of the building above the base level.

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7.2.5. The seismic design force determined as per 7.2.1 or 7.2.2 shall not be lower than

0.8A0Pp/g. 7.3. Forces for anchoring design 7.3.1. All secondary elements and equipment shall be duly anchored to the resistant structure by

means of bolts or other devices. The design shall be made with the forces established in 7.2 with the modifications detailed under 7.3.2 and 7.3.3.

7.3.2. When the anchorage to concrete elements includes anchor bolts on the surface (bolts with

a length-diameter ratio under 8), the seismic forces established under 7.2 shall be in-creased by 50%, or else, they shall be calculated with Rp = 1.5. The same provision shall be applied to anchor bolts designed without the exposed length specified under 8.6.2.

7.3.3. When the anchoring system is built with non ductile materials, the seismic forces of 7.2

must be amplified by 3, or else be calculated with Rp = 1.0. 7.4. Automatic shutoff systems

Ducts, vessels and equipment containing high temperature gases and liquids, explosives or toxic materials must be equipped with automatic shutoff systems which fulfill the pro-visions of 8.5.4 of NCh433.Of96.

Table 7.1 - Maximum values of the response modification factor of

secondary elements and equipment

Secondary elements or equipment

Rp

- Rigid or flexible equipments or elements with non-ductile materials or appendages

1.5

- Precast secondary elements. Elements in cantilever. Partitions.

- Electric and mechanical equipment in general. - Stacks, tanks, steel towers - Other non specified cases in this table

3

- Storage shelves - Secondary structures

4

8. Special provisions for steel structures 8.1. Applicable standards

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Until the issuance of the new edition of the Chilean Standard on detailing and construc-tion of steel structures, the provisions of this standard shall be used complemented with the following standards:

a) Load and Resistance Factor Design Specifications for Steel Buildings, 1999, Ameri-

can Institute of Steel Construction (AISC); or Specifications for Structural Steel Buildings, Allowable Stress Design; 1989, AISC.

b) Specifications for the Design of Cold Formed Steel Structural Members, 1996, Ameri-

can Iron and Steel Institute (AISI), covering the design of cold formed elements not included in the AISC standards

c) In matters of seismic design, the AISC standards shall be supplemented by the provi-

sions of Seismic Provisions for Structural Steel Buildings, Part 1: Structural Steel Buildings, 1999, AISC, or the provisions contained in clause 8 and Appendix B of this standard.

8.2. Materials 8.2.1. Structural steel shall fulfill the following provisions:

- Exhibe at tensile testing a pronounced natural ductility plateau with a yield point under 0.85 times of the ultimate strength and minimal fracture elongation of 20% in 50 mm test specimen.

- Guaranteed weldability in conformance with AWS standards.

- Minimum toughness of 27 at 21ºC measured with Charpy test compliant to ASTM 6.

- Yield point not over 450 Mpa.

8.2.2. In addition to the conditions specified under 8.2.1 , the materials shall fulfill one of the

following specifications:

- ASTM A36; A242; A572 Gr. 42 and Gr. 50; A588 Gr. 50; A913 and A982 for structural shapes; plate; bars; common bolts and anchor bolts).

- DIN 17 100, qualities St. 44.2; St. 44.3 and St. 52.3 for the same foregoing elements.

- NCh203 A 42-27ES; A 37-24ES; and NCh1159 A 52-34ES for the same foregoing ele-

ments.

- ASTM A500 Gr. B and C; A501 and A502 for structural tubes.

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- AWS 5 for welding.

Materials that meet other than the foregoing specifications may be used prior approval by the professional specialists of each project.

8.2.3. Earthquake-resistant groove welds shall be complete joint-penetration type with elec-

trodes of minimum toughness of 27 Joules at -29 ºC, measured with Charpy test according to ASTM A6.

8.3. Braced frames 8.3.1. Braced frame configurations with diagonal elements that only resist tension are not al-

lowed, except in case of light steel bays, which are governed by the provisions detailed under 11.2.

8.3.2. Every resistant line shall include braces to take tension and braces to resist compression.

As a minimum the strength provided by the diagonal resisting tension in each direction of the seismic action, shall be equivalent to 30% of the shear load of the resisting line at the corresponding level.

8.3.3. The elements of vertical earthquake-resistant systems under compression shall have

width to thickness ratios under rλ according to Table 8.1 (see Figure 8.1). The slender-ness ratio of the element shall be less than 1.5 yFE /π .

8.3.4. The diagonal elements in an X brace shall be connected at the point of intersection. This

point can be considered fixed in perpendicular direction to the plane of the braces for de-termining the member’s buckling length when one of the diagonal elements is continuous.

8.3.5. In industrial buildings with V-bracing or inverted V-bracing bracing, beams shall be con-

tinuous over the intersection point with the diagonal elements and they shall be designed to resist the vertical loads assuming that they are not supported by the diagonal elements. In addition, the diagonal elements shall be capable of supporting the self-weight loads and the beam-induced live loads plus the seismic loads gotten from analysis, amplified by 1.5. The upper and lower beam flanges shall be designed to resist a transversal load located at the point of intersection with the diagonal elements, equal to 2% of the nominal strength of the flange, that is, Fy bf t ,

where

Fy = yield stress of the flange; bf = width of the flange t = Flange thickness

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8.3.6. The earthquake stress in the compressed diagonal elements shall be less or equal to 80% of the resistant capacity defined in the steel design specification.

8.3.7. Seismic K-braces in which the diagonal elements intersect in an intermediate column

point are not allowed, except that at that point exists a strut that is part of the bracing sys-tem.

8.3.8. Provisions 8.3.3, 8.3.5, and 8.3.6 shall not be applied to bracings whose majorated earth-

quake stresses are lower than one third of the stresses of the combination that controls the design.

8.4. Rigid frames 8.4.1. Moment connections of earthquake-resistant rigid frames shall be totally rigid (TR). Par-

tially rigid (PR) connections are not allowed. These connections shall be designed so that to enable the development of the plastic hinge in the beam at a reasonable distance from the column, which can be achieved by reinforcing the connection or weakening the beam at the desired position of the plastic hinge.

8.4.2. Abrupt changes of the beam flange width are not allowed at the potential plastic hinge

development areas or near them, unless when dealing with a reduced beam section appro-priately designed to induce the plastic hinge at that position.

8.4.3. The transversal sections of the columns and beam beams in rigid earthquake-resistant

frames shall qualify as compact, that is, their width to thickness ratios shall be under pλ of Table 8.1.

8.4.4. In multi-story structures in which the total earthquake-resistance depends from rigid

frames designed with R1 greater or equal to 3, the sum of the bending strength capacities of the columns that concur at a node shall be greater or equal to 1.2 times the sum of the bending strength capacities of the connected beams.

It is not necessary to fulfill this requirement in whichever of the following cases:

a) If the seismic shear load of every column for which the abovementioned requirement

is not met, is 25% lower than the seismic shear load of the corresponding story.

b) If the analysis and detailing of the structure is made by taking seismic forces equal to the double of the values established under clause 5 of this standard.

c) If a non-linear analysis (see 5.2.3) proves that the structure is stable in the face of the

deformation demands imposed by the earthquake. 8.4.5. The design of the beam-column panel zone of earthquake-resistant rigid frames shall be

compliant to Appendix B.

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8.4.6. The compression strength in columns with prevailing compression, disregarding the ef-

fect of the flexural moment, shall be greater than the axial loads obtained from the loading combinations of 4.5, in which the earthquake loading condition of these loading combina-tions has been amplified by 2. Prevailing compression is defined as the situation in which the axial stress obtained from the loading combinations of 4.5 is greater than 40% of the design compression strength of the column.

8.4.7. The provision of 8.4.3 is not applicable to rigid frame elements in which the stresses from

majorated seismic loads are lower than one third of the stresses of the load combination which controls the design.

8.5. Connections 8.5.1. Materials shall fulfill the following requirements:

- The bolts of earthquake-resistant connections shall be exclusively high strength mate-rial, quality ASTM A325 or ASTM A490, or equivalent.

- Arc welding electrodes and fluxes shall be compliant to AWS A 5.1, A 5.5, A 5.17, A

5.18, A 5.20, A 5.23, and A 5.29 or equivalent specifications.

- Electrodes shall feature a minimum Charpy toughness of 27 Joules at –29ºC according to ASTM A6.

8.5.2. The connections of seismic diagonal elements shall be designed to resist 100% of the ten-

sile capacity of their gross section. 8.5.3. The moment connection strength between beams and columns of rigid earthquake-

resistant frames shall be at least equal to the strength of the connected elements. 8.5.4. The upper and lower beam flanges in beam-column connections of rigid frames shall have

lateral supports designed for a force equal to tbF02.0 fy . 8.5.5. The groove welds of earthquake-resistant joints shall be of complete penetration type. 8.5.6. High-strength bolts shall be installed with the pretension specified for slip-critical connec-

tion (70% of tensile strength for A325 and A490 bolts). However, the design strength of bolted joints can be calculated as that corresponding to bearing stress connections. The contact surfaces shall be cleaned with mechanical roller, or by sand blasting or shot blast-ing; they shall not be painted but galvanizing is acceptable.

8.5.7. Not allowed are connections whose resistance depends on a combination of weldings with

high-strength bolts or rivets. Excepted are the modifications of existing riveted structures.

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8.5.8. Field joints shall fulfill the following requirements:

a) In connections made with high-strength bolts, methodologies of tightening and control that assure the pretension required under 8.5.6 shall be applied.

b) Welding is allowed only in plane position, vertical and horizontal, and with the welder

protected against wind and rain.

c) Welds shall be complete-penetration groove welds or filet-welds. Groove welds shall be controlled by means of ultrasonic or X-ray.

8.5.9. Column splices shall fulfill the following conditions:

a) In buildings the distance between the column splice and the upper beam flange shall be greater or equal than the lower value between 900 mm and half of the clear column height.

b) The splices shall be sized for the design forces obtained from the load combinations of

4.5, in which the seismic load condition has been amplified by 2. 8.6. Anchorages 8.6.1. The supports of structures and equipments, which transfer seismic loads to the founda-

tions or other concrete element, shall be anchored by means of anchor bolts, anchor plates, reinforcing bars or other appropriate means.

8.6.2. Anchor bolts subjected to tension according to the procedures of analysis detailed under

clauses 4, 5 and 7 shall have chair and the bolt shall be visible for allowing their inspec-tion and repair and the thread shall have the sufficient length to enable retightening of the nuts (see Appendix A, Figure A.1). The exposed length of the bolts shall not be less than 250 mm nor eight times their diameter, nor the thread length under the nut be less than 75 mm.

Exception is made to this requirement for anchor bolts with sufficient capacity to resist loading combinations, in which the seismic loads are amplified by 0.5 R times, but not less than 1.5 times, the value specified in clauses 5 and 7.

Important equipments, such as very high process vessels and in the structure of large sus-pended equipments, such as boilers and similar facilities, shall be outfitted with bolts of high ductile deformation capacity, which are easily repairable and eventually could be re-placed (see Appendix A, Figure A.7).

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8.6.3. Base plates of columns and equipments in general shall be outfitted with shear keys or seismic stoppers designed for transferring 100% of the base shear load (see Appendix A, Figure A.1).

Excepted from this requirement are the following cases:

a) Supports with shear load under 50 kN; in this case it will be allowed to resist the shear

load with anchor bolts, considering that only two of them are active to this purpose as well as the corresponding shear-tension interaction formulas.

b) Tanks and equipments bases outfitted with nine or more anchor bolts; in this case it

will be accepted to resist 100% of the shear load with the anchor bolts, considering that only one third of the total number of anchor bolts is active and applying the corre-sponding shear-tension interaction formulas with the maximum tension and the shear force so calculated.

c) Tanks of aspect ratio (height/diameter) under one, which do not require anchorage ac-

cording to 11.8. In this case, the shear can be taken by means of conicity at the base.

In cases a) and b) the anchor bolts shall be embedded in the foundation.

8.6.4. The leveling mortar strength shall not be taken into account in the design of the shear plate.

8.6.5. The design of the shear anchorage elements shall not consider the friction between the

base plate and the foundation. 8.6.6. The superposition of the shear plates strength and that of the anchor bolts is not allowed. 8.6.7. When void boxes are laid on the foundation for the later installation of anchor bolts, the

lateral walls of these void boxes shall have a minimal pitch of 5% with respect to the ver-tical, so that the lower area is greater than the upper one. The void boxes shall be filled with non-shrinking mortar.

8.6.8. The concrete for the foundation shall be designed to resist the vertical and horizontal

loads transferred by the metal anchor elements. The concrete strength and its reinforce-ments shall be such that the eventual failures affect the metal anchor elements but not the concrete.

8.7. Horizontal bracing systems 8.7.1. The following provisions are applicable to buildings and industrial facilities with floor or

roof steel bracing system, the function of which consists in transferring the seismic design loads and/or to provide structural redundance for fulfilling the requirements of this stan-dard for specific structures.

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8.7.2. Diagonal configurations of floor and roof bracing systems, designed to only take tension

are not allowed, except in light steel bays, which are ruled by the provisions under 11.2. 8.7.3. For floor and roof bracing systems whose function is to transfer and/or share the seismic

loads that control the design, which are tributary of one or more frames (overhead travel-ing cranes, large suspended equipment, etc.) to other adjoining or remote rigid frames or bracings, the design provisions detailed under 8.7.3.1 to 8.7.3.4, shall be applied.

8.7.3.1. Earthquake-resistant diagonal elements and struts working in compression shall have

width to thickness ratios under rλ according to Table 8.1 (see Figure 8.1). The slender-ness of the element shall be less than 1.5 yFE /π .

8.7.3.2. The diagonal elements in X shall be connected at the point of intersection. Said point

can be considered fixed in perpendicular direction to the diagonal elements plane for the purpose of determining the buckling length of the piece when one of the diagonal ele-ments is continuous.

8.7.3.3. The provision 8.7.3.1 is not applicable to bracings whose loads, obtained from the load

combination that include seismic loads, are lower than one third of the loads that control the design.

8.7.3.4. The provision 8.7.3.1 is neither applicable when the design of the bracing system is car-

ried out with the loads obtained from the loading combinations that include seismic loads, in which this latter load has been amplified by 0.7 R.

8.7.4. Roof or floor bracing systems that provide structural redundance in accordance with the

requirements of specific structures, shall fulfill the following requirements: 8.7.4.1. The horizontal bracing system and its connections shall be designed according to the

provisions of 8.1 a) or b), as appropriate. 8.7.4.2. The seismic loads to be considered for horizontal bracing systems shall not be lower

than the seismic contribution of an intermediate frame under eventual premature fail-ure (see Figure 8.2).

8.7.5. The section height of the diagonal elements and struts of roof and floor bracing systems

shall be greater than or equal to 1/90 of the horizontal projection of the length of the ele-ment.

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Table 8.1 – Limits of the width to thickness ratio (for definitions see 3.2 and Figure 8.1)

Action that affects the structural member

Compression Bending

Shapes

λ λr λr λp

Double T, rolled, welded or hybrid, and rolled channels Unstiffened flanges, rolled I and C sections

b/t 0.56 yFE / 0.83 )70/( −yFE 0.38 yFE/

Unstiffened flanges, welded, built in and hybrid sections

b/t 0.64 yc F/Ek *) )115/(95.0 −yfc FEk *) 0.38 yFE/

All webs **) ***) h/tw yFE /49.1 yFE /7.5 yFE /76.3

If 125.0/ ≤ybu PP φ

λr λp

h/tw

70.5 ⎟⎟⎠

⎞⎜⎜⎝

φ−

yb

uy P

P74.01F/E ⎟

⎟⎠

⎞⎜⎜⎝

⎛−

yb

uy P

PFEφ75.21/76.3

If 125.0/ ≥ybu PP φ

λr λp

Webs in combined bending, all **) ***)

h/tw

70.5 ⎟⎟⎠

⎞⎜⎜⎝

φ−

yb

uy P

P74.01F/E y

yb

uy FE

PPFE /45.133.2/12.1 ≥⎟

⎟⎠

⎞⎜⎜⎝

⎛−φ

Stiffened flanges and any other stiffened element by a stiffener that is capable of providing an effective edge support

b/t or h/tw

yFE /49.1

yFE /49.1

yFE /12.1

Flange stiffeners, or web longitu-dinal stiffeners

c/t 0.64 yc F/Ek *) 0.56 yFE / 0.38 yFE/

Vertical web stiffeners b/t 0.56 yFE / NA NA

Splice plates in compressed flanges

b/t yFE /40.1 yFE /40.1 yFE /12.1

Tee shapes Flanges, rolled sections b/t 0.56 yFE / )70/(83.0 −yFE 0.38 yFE /

Flanges, welded sections b/t 0.64 yc F/Ek *)

)115(95.0

−yf

c

FEk *)

0.38 yFE /

Webs **) d/tw 0.75 yFE / NA NA

Rectangular of uniform thick-ness: Flanges Web

b/t h/tw

yFE /40.1

yFE /40.1

yFE /40.1

yFE /70.5

yFE /12.1

yFE /76.3

(continues)

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Table 8.1 – Limits of the width to thickness ratio (conclusion) (for definitions see 3.2 and Figure 8.1)

Tubular Shapes Welded rectangular with flanges thicker than the web: Flanges Web

b/t h/tw

yFE /49.1

yFE /49.1

yFE /49.1

yFE /70.5

yFE /12.1

yFE /76.3

Round shapes D/t 0.11 E/Fy 0.31 E/Fy 0.071 E/Fy Struts composed of rolled angle shapes

Flanges of simple angle shapes, LT shapes with sepa-rators, XL shapes and unstiff-ened elements in general

b/t

0.45 yFE / NA NA

Flanges of LT sections with in-contact angles

b/t 0.56 yFE / NA NA

Cold bent sections Unstiffened flanges of C or Z shapes

b/t 0.42 yFE / 0.42 yFE / 0.30 yFE /

Stiffened flanges of CA, ZA, Ω and hat shapes

b/t 1.28 yFE / 1.28 yFE / 1.08 yFE /

Flanges of simple angle shapes , TL and XL shapes, with or without separators

b/t 0.37 yFE / NA

NA

Webs of C, CA, Z, ZA, Ω and hat shapes

h/tw 1.28 yFE / 3.13 yFE / 2.38 yFE /

Stiffening flanges c/t 0.42 yFE / 0.42 yFE / 0.3 yFE /

λr λp

If 15.0/ <ybu PP φ

3.13 yFE / ⎟⎟⎠

⎞⎜⎜⎝

φ−

yb

uy P

P33.21F/E38.2

If 15.0/ ≥ybu PP φ

Webs of C, CA, Z, ZA, Ω and hat shapes in combined bend-ing

h/tw

3.13 yFE / 1.5 yFE /

NOTES NA = not applicable E,Fy; in MPa E = 200,000 MPa λr = limit of width to thickness ratio to prevent local buckling

*) kc = wth /

4 but within the range 0.35 ≤ kc ≤ 0.763

λp = limit of width to thickness ratio to allow complete plastifica-

tion of the section

**) For hybrid beams use Fy, of flanges

***) In unequal flange members use hc instead of h when comparing with λp.

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Figure 8.1 Examples of width to thickness ratios of table 8.1 (Flat widths b and h according to definitions of terms in 3.2)

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Figure 8.2

9. Special provisions for concrete structures 9.1. Reinforced concrete structures 9.1.1. Until the official issuance of the new edition of the Chilean standard NCh430 that re-

places standards NCh429.Of57 and NCh430.Of61, the provisions of the ACI Code 318-99 shall be used, in those that are not in contradiction with the provisions of this standard. For the effects of the application of Chapter 21 of said ACI Code (paragraph 21.2.1), it shall be considered that the complete national territory with its three seismic zones corre-sponds to high seismic risk.

9.1.2. The structural elements that are part of ductile frames designed to resist earthquake loads

shall be designed and detailed as special moment resistant frames, according to the provi-sions of ACI 318-99, chapter 21, sections 21.1 to 21.5.

9.1.3. Frames which belong to structures whose earthquake loads have been calculated with an

R1 factor under or equal to 2 can be designed according to the provisions for intermediate moment resistant frames, as per ACI 318-99, chapter 21, section 21.10. The same provi-sion can be applied to frames with seismic deformations lower or equal to 50% of the lim-iting value established under 6.3.

9.1.4. In the case of structures with a combination of reinforced concrete walls and frames

where the set of walls resists at each level and in each direction of analysis a percentage of the total shear load of the level that is greater or equal to 75%, the design of the frames can be carried out according the requirements of section 21.10 of ACI 318-99, chapter 21,

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provided the frame is responsible for resisting less than 10% of the total shear loads from each and every level.

9.1.5. Frames in which the seismic loads do not control the design and whose failure does not

affect the stability of the structure, can be designed according to the provisions of ACI 318-99, chapter 21, section 21.9.

9.1.6. It is not required that the design of walls fulfill the provisions of ACI 318-99, chapter 21,

section 21.6.6.3. 9.1.7. In multi-story structures in which the earthquake resistance depends from rigid frames

designed with R1 values that are higher than or equal to 3, it is not necessary to fulfill the requirement of strong column – weak beam (ACI 318-99, 21.4.2) when one of the follow-ing conditions is met:

a) the seismic shear load of the groups of columns for which the foregoing provision is

not accomplished, is lower than 25% of the seismic shear load of the corresponding story;

b) if the analysis and design of the structure is carried out with seismic forces equal to

two times the values detailed under clause 5 of this standard.

c) If it can be proved by means of a non-linear analysis (see 5.2.3) that the structure is stable when facing the deformation demand of an earthquake.

9.2. Precast concrete structures 9.2.1. Requirements for precast systems 9.2.1.1. Structures that include precast concrete elements shall be designed to resist seismic ac-

tions according to some of the following criteria:

a) Gravitational systems

The earthquake-resistant system in this case comprises reinforced concrete, casted-in-place walls or frames, confined or reinforced masonry walls or braced or non-braced steel frames. Precast elements are used to resist exclusively the vertical loads.

The precast elements and connections that do not belong to the earthquake-resistant sys-tem shall be capable of accepting the seismic deformation, d, of the structure and resist the vertical (gravitational) loads for that deformation. The frames belonging to the precast gravitational system can be designed in accordance with the provisions of the ACI Code 318-99, section 21.9.

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The joints between the precast gravitational system and the earthquake-resistant system shall be considered as part of this latter system and shall be designed according to para-graphs b), c) or d).

b) Precast systems with wet connections.

These system emulate the behavior of cast-in-place reinforced concrete structures by means of the use of precast elements connected by wet connections that fulfill the re-quirements of ACI Code 318-99, especially those relative to the anchorage and bar splic-ing.

c) Precast systems with ductile connections

These structures consist of precast elements joined by means of connections that have been proved by non-linear cyclic analysis and tests to have strength and ductility greater than or equal to the monolithic connections of structures designed according to the ACI Code 318-99. These tests shall meet the requirements of the document ACI ITG/T1.1-99 Acceptance Criteria for Moment Frames based on Structural Testing; they can be per-formed by local or foreign laboratories, provided that their results are certified by a labo-ratory approved by the Chilean Ministry of Housing and Urbanism.

d) Precast systems with dry connections

These structures consist of precast elements joined by means of dry connections that have been designed as strong connections that assure that an eventual non-linear behavior in case of earthquakes of higher demands than those considered in this standard produce an incursion within the non-linear response range in sections far from the strong connection.

These precast systems accept an earthquake-resistant system exclusively composed of walls connected with dry connections or one exclusively composed of frames connected by dry connections.

Structures with an earthquake-resistant system exclusively composed of a precast system with dry connections are allowed to be built only up to 4 levels and a maximum height of 18 m, measured from the base level.

9.2.1.2. Structures that include precast gravitational systems shall be designed considering the earthquake loads that correspond to the earthquake-resistant system being used.

Precast systems with wet connections and ductile connections shall be designed using the earthquake loads corresponding to a monolithic reinforced concrete structure.

9.2.1.3. 9.2.1.3 Precast systems with dry connections shall be designed with the values listed in

Table 5.6 for cast-in-place reinforced concrete structures. However, the value of R shall not be greater than 4 and the damping ratio not greater than 0.03 for bolted connections

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and connections by means of bars embedded in filling mortar, nor greater than 0.02 for welded connections.

The compliance with the behavior requirements detailed in 9.2.1.1 c) demands that dry connections must meet the provisions 9.2.1.4 and 9.2.1.5.

9.2.1.4. In precast systems with dry connections, the quotient between the nominal strength of

the connection and that of the element connected at the point of connection (Se) shall be greater than or equal to 1.4.

9.2.1.5. Dry connections of precast frame structures shall be capable of developing under bend-

ing, shear or axial load or combination of these actions acting on the connection, a probable strength Spr determined by using a value Ф = 1, not under 125% of the yield strength of the connection and they shall be able of developing a displacement under Spr that shall not be less than 4 times the yield displacement. The anchorage of the connec-tion in the precast element at any side of the connection shall be designed to develop a stress equal to 1.3 times Spr. In addition, the connection shall meet the requirements of confinement if fc is greater than 0.7 f’c.

The above established behavior shall be guaranteed by means of tests that include the cyclic feature of the action. The tested samples shall be representative of the proposed system. The tests shall be compliant to the ASTM specifications on instrumentation and performance of cyclic testing.

9.2.1.6. The steel and electrodes used in welded connections shall meet the provisions estab-

lished under 8.2.2 and 8.5.1. 9.2.1.7. If the base shear Q0 is lower than the following value

PgA

I40.0Q 0min = (9.1)

all deformations and stresses shall be multiplied by the quotient Qmin/Q0 for design pur-poses.

The foregoing provision shall not be applied to precast concrete structures classified un-der 9.2.1.1 as gravitational systems or precast systems with wet connections and ductile connections, which shall meet the provision on minimum base shear detailed under 5.4.5.

9.2.2. Special provisions 9.2.2.1. The design of precast elements and connections shall include the load conditions and

deformation occurring from the initial fabrication until the completion of the structure, including removal of forms, storage, transport and installation.

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9.2.2.2. The design of precast elements and their connections shall include the effect of fabrica-

tion tolerances. 9.2.2.3. In addition to the requirements on drawings and specifications of this standard, the fol-

lowing data shall be included in shop drawings:

a) Details of reinforcement, inserts and hoisting devices those are required for resisting the temporary loads of handling, storage, transport and installation.

b) Concrete strength at the ages or established construction stages.

9.2.2.4. Not allowed is the use of connections that are based exclusively on the friction caused

by gravitational loads. 9.2.2.5. A slab composed of precast elements shall be considered to be a rigid diaphragm, pro-

vided that an overslab that meets the provisions detailed under the ACI Code 318-99, sections 21.7.2; 21.7.3; 21.7.4; and 21.7.5 is considered in the design.

9.3. Industrial bays composed of cantilever columns 9.3.1. This paragraph establishes the special requirements of industrial bays, with or without

overhead traveling cranes, built with cast in place or precast concrete columns and struc-tured with built in columns at the base and beams connected to the columns with hinged connections. The earthquake-resistance and deformation capacity of these systems come exclusively from the columns.

9.3.2. The bays shall have a continuous roof bracing system connected to the upper level of the

columns.

If the bracings are provided by steel shapes, these shall meet the provisions of 8.7.

If the bracing is provided by a different system, this shall feature a stiffness that is equiva-lent to that of a steel system with braces composed of shapes designed to only work in tension and meet 8.1.a) or 8.1.b). Such other system cannot be composed of elements de-signed to only work in tension.

9.3.3. The seismic design of structures, which fulfill 9.3.1 and 9.3.2 shall be carried out with R

= 3 and with a damping ratio of 0.02. 9.3.4. The base shear load shall not be less than:

Qmin = 0.4 I A0P / g

(9-2)

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In those cases where the base load Qo is lower than the foregoing values, the stresses and deformations shall be multiplied by Qmin / Q0 for the purpose of the design.

9.3.5. The design of the elements shall be made according to the provisions of 9.1 for cast-in-

place concrete elements and according to 9.2 for precast concrete elements.

The base of the columns shall be designed with a confinement length that is longer than or equal to twice the height of the transverse column section according to ACI 318-99, sec-tion 21.3.3.

9.3.6. The maximum column slenderness shall meet

l = k L / r ≤ 100 (9-3)

Unless appropriately justified, the value of k shall be 2. 9.3.7. The beams shall be laterally supported to prevent their overturning due to the action of

purlins or secondary beams. In consequence, the load-bearing beams shall be provided with lateral bracings.

9.3.8. It shall not be accepted that non concrete cover plates provide lateral bracing for any ele-

ment. 9.3.9. Column heads shall be connected with strut beams in two orthogonal or approximately

orthogonal directions. 9.3.10. The seismic loads to be considered for horizontal bracing systems shall not be smaller

than the seismic contribution of an intermediate frame in eventual premature failure (see Figure 8.2).

9.3.11. The calculus of deformations shall satisfy 6.1 and the requirements of 6.2 and 6.3 shall

be fulfilled.

Maximum horizontal deformations shall be calculated by modifying the formula 6-1 as follows

D = d0 + S0 R1 dd (9-4)

considering the following values of S0 :

1.00 for soil I 1.25 for soil II 1.50 for soil III 9.3.12. The consideration of the P-Delta effect shall satisfy 6.4.

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9.3.13. The design of the columns and foundations resting on soils type III shall consider the

rotation of the foundations for the calculus of stresses as well as for deformations. To this end, a geotechnical study shall be carried out to get the maximum and minimum values of the modulus of subgrade reaction. The stress calculation shall be made with the maximum modulus of subgrade reaction and deformations with the minimum.

It shall not be accepted to support foundations on soil type IV.

10. Provisions for foundations 10.1. General design provisions 10.1.1. The foundations shall reflect the hypotheses of the corresponding model of analysis as

much in their geometry as in their stiffness and mass characteristics.

Massive foundations can be considered to lack elastic properties. However, isolated foundation systems connected by foundation beams and foundation slabs, shall be as-sumed to have inertial as well as elastic properties.

The dimensions of foundations assumed to be infinitely rigid and resting on flexible soil, shall be consistent with this hypothesis.

10.1.2. The dimensioning by strength of the foundation shall be carried out for all the load

combinations considered in the design of the rest of the structure. 10.1.3. Verification of soil induced stresses its deformation and the stability of the foundations

shall be carried out for all the applicable non-factored load combinations. 10.1.4. The appropriate behavior of the foundations shall be verified regarding the action of

static as well as of seismic loads, verifying that the contact pressure between soil and foundation is such that the induced deformations are acceptable for the structure.

10.2. Shallow foundations 10.2.1. Unless the geotechnical report imposes higher restraints, at least 80% of the area below

each isolated foundation or foundation slab shall be under compression.

This restraint is not applicable in cases where anchorages between foundation and soil are used.

10.2.2. The calculation of seismic actions induced at the base of buried foundations under

ground level may disregard the inertial forces developed by the masses of the structure located under the level of the natural soil as well as the ground’s seismic thrusts, pro-

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vided the foundation has been built against natural soil or the earth fills between the foundation and the natural soil has been duly compacted and controlled.

10.2.3. The foundations subjected to non-factored load combinations that include earthquake,

which develop net tensions in them, shall resist these tensions only with self-weight, warranting a minimum safety factor of 1.5 against uplift.

11. Specific structures 11.1. Industrial buildings 11.1.1. These provisions shall be applied to industrial buildings with or without traveling crane

supporting beams. 11.1.2. Buildings with transverse frames shall be outfitted with a continuous roof bracing sys-

tem. In the presence of roof trusses the continuous bracing shall be placed on the plane of the lower chord of the truss. Exception to this provision is made for buildings without traveling cranes, where permanent loads result only from self-weight (see Appendix A, Figure A.2).

11.1.3. The seismic analysis of buildings with overhead traveling cranes shall be made consid-

ering the magnitude and height of the most probable suspended loads during the design earthquake. Therefore the occurrence frequency of the design earthquake and the oper-ating conditions of the cranes shall be considered.

11.1.4. In case of more than one crane in a bay or in parallel bays, the design shall consider a

seismic load combination with all the cranes unloaded and parked at the most unfavor-able position.

11.1.5. The lateral connection between crane girders and columns shall be flexible in the verti-

cal direction. Also to be considered are the safety devices that prevent the falling of the bogie in case the wheels run out of the rails (see Appendix A, Figure A.3).

11.1.6. In buildings with rigid frames, the bracings of the endwalls whose purpose is the lateral

support of the columns designed for wind loads, shall not provide greater lateral stiff-ness than that provided by the interior frames, unless they are considered in the struc-tural model as specified in 5.3.1.1 (see Appendix A, Figure A.4).

11.1.7. In case the building is flexible and has non-structural rigid masonry walls or walls of

analogous materials, the design shall include connections capable to support the walls laterally and allow independent longitudinal displacement between the walls and the structure (see Appendix A, Figure A.5).

11.2. Light steel bays

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11.2.1. The subsequent provisions shall be applied to steel buildings that fulfill the following conditions:

- They are structured as a succession of parallel frames composed of columns and beams,

of truss type, open shapes of solid web, or closed shapes.

- The inner clearance of the lateral columns shall be smaller than or equal to 15 m. This requirement can be obviated if in the loading combinations indicated in 4.5, the seismic forces resulting from the analysis are amplified by 2.

- The transverse distance between adjoining column axes shall be shorter than or equal to

30 m. This requirement can be obviated if in the loading combinations indicated in 4.5, the seismic forces resulting from the analysis are amplified by 2.

- The building can comprise one bay or several parallel bays.

- The earthquake-resistant structure corresponds to parallel rigid frames, or else to end or

intermediate rigid or braced frames, which receive the horizontal seismic forces through a roof bracing system.

- The structures shall qualify under categories C2 or C3 according to 4.3.1.

- The nominal capacity of the overhead traveling cranes shall be less than or equal to 100

kN in case of cranes without operator cabin, or 50 kN in cranes with operator cabin.

- The equipment supported by the structure shall have a weight per frame under or equal to 100 kN.

- The horizontal seismic load the garret transmits to each column of the structure shall not

be higher than 15 kN.

- They have no storage racks, which are seismically supported by the structure. 11.2.2. The determination of the seismic design forces shall consider the damping ratios of Ta-

ble 5.5 and a response modification factor under or equal to 4. 11.2.3. The design of light steel bays shall fulfill the provisions of clause 8, excepting 8.3.3,

8.3.5, 8.3.6, 8.4.1, 8.4.2, 8.4.3, 8.4.4, 8.4.5, 8.4.7, 8.5.2, 8.5.4 and 8.5.9, the application of which is not mandatory.

11.2.4. The diagonal elements of the bracing system designed only to resist tension, shall be

inspection able and be outfitted with adequate devices for initial tensing and subsequent adjustment.

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11.2.5. The diagonals of the seismic roof bracing designed exclusively to resist tensile forces, shall have a capacity that at least corresponds to the sum of the initial prestress and the seismic forces resultant from the analysis, amplified by 1.5.

11.2.6. The roof brace system designed to transmit horizontal forces to the transversal end

frames, shall be continuous and be composed of diagonal and strut elements that work under tension as well as compression.

11.2.7. The vertical bracing system shall correspond to diagonal elements and struts, designed

to work under tension as well as compression and their slenderness shall be smaller than or equal to 1.5 yFE /π . This requirement is not mandatory in bays with spans be-tween columns of less than or equal to 12 m and shoulder height of less than or equal to 6 m. In such cases it is allowed to use elements that work only in tension, provided they are compliant to the requirements of 11.2.4 and 11.2.5.

11.2.8. The seismic design of the connections of the vertical and roof bracing systems shall be

carried out considering the load combinations detailed under 4.5 with the seismic forces resultant from the analysis amplified by 1.5.

11.2.9. The seismic deformations shall be determined in accordance with the requirements of

6.1 and shall be limited to values that prevent damages to piping, hoisting and transport equipment, electric systems and other elements joined to the structure, which is to be protected. It is not mandatory to fulfill the provisions of 6.3 and 6.4.

11.2.10. The separation between structures shall fulfill the provisions of 6.2.1. 11.2.11. In light steel bays that do not consider the system described under 11.2.6 neither include

overhead traveling cranes or equipment mentioned under 11.2.1, the roof panel can be considered to be a rigid diaphragm capable of transferring the seismic forces to the lat-eral bracing systems, provided its capacity to transfer this shear load is certified by means of static tests with cyclic load. The safety factor with regard to the experimental value shall be that of AISI 1996, clause 2.

The design of the diaphragm shall satisfy the ICBO ES document AC43, Acceptance Criteria for Steel Decks of July 1996 and the AISI standard as supplement. The load combinations detailed in 4.5 shall be used with the seismic forces resultant from the analysis, amplified by 2.

The tests shall be analyzed by competent, independent internationally renowned organi-zations and be performed on samples, which consider the deck panel action and its fas-tening system to the support structure (sidings), the same as these will be implemented on site.

The company which certifies its panels also shall concern with the quality and correct installation of the fastening system.

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11.3. Multi-story industrial buildings 11.3.1. To the extent to be possible, floors shall be rigid seismic diaphragms, which may be of

concrete or metal with horizontal bracings or solid floor plates. Diaphragms shall in-clude devices for connection with the structure, which shall be capable of transferring the seismic forces.

11.3.2. Rigid ducts or equipments vertically extended over more than one story shall be outfit-

ted with bearing and connecting systems that prevent their participation in the strength or stiffness of the building (see Appendix A, Figure A.6). If this is not possible, the equipment shall be included in the model of the earthquake-resistant system.

11.4. Large suspended equipment 11.4.1. Boilers, metallurgical furnaces, and other large suspended equipments from the struc-

ture, shall be attached to it by means of connectors that transmit the seismic forces with-out restraining the free vertical or horizontal thermal expansion (see Appendix A, Fig-ure A.7).

11.4.2. For suspended electric equipments that cannot be attached horizontally to the structure,

such as the electrode cages of electrostatic precipitators, special isolators with ample strength capacity shall be specified as well as devices for the interruption of electric power supply in case of severe earthquakes. If exists the possibility of an impact of the electrode cage with the equipment shell or with the collector plates, the system shall be outfitted with impact plates.

11.5. Piping and ducts 11.5.1. Large piping and duct systems shall be equipped with expansion joints and supports that

warrant seismic stability and simultaneously allow thermal expansion. 11.5.2. If piping and ducts are light in relation to the buildings or structures they connect, the

seismic analysis can be carried out introducing the deformations dd according 6.1 for the buildings or structures, at the points of connection. In the opposite case, an analysis of the structure-duct combination as one unit shall be carried out.

11.6. Large mobile equipment 11.6.1. Large mobile equipments such as bulk material loaders and unloaders, stackers, travel-

ing cranes and similar equipments shall be dynamically analysed, considering the mag-nitude and the most unfavorable positions of the loads. The analysis can be carried out assuming that the wheels are pivoted on rails or floor, but if significant uplifting is in-volved, counterbalance devices for safety shall be included. (see Appendix A, Figure A.8).

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11.6.2. The system shall be self-centering to reduce the possibilities of impacts between the rail

flanges and wheels (see Appendix A, Figure A.9). 11.6.3. Special attention shall be laid on the effects of the seismic eccentricity that occur in

these systems. 11.7. Elevated tanks, process vessels and steel stacks 11.7.1. Elevated tanks shall be designed considering the mobility of water. 11.7.2. Process vessels shall be designed with special attention to the joint of the supports to the

shell when this does not extend down to the foundation. 11.7.3. Elevated stacks shall be designed by the dynamic method. When the duct for the gases

is not self-supporting, the interaction between the duct and the external steel or concrete structure shall be considered. The inner concrete coating, where existent, shall be con-sidered for the purpose of calculating stiffness but not of strength.

11.7.4. The shell shall be designed to prevent local buckling considering the effect of lateral

and vertical design forces as well as the fabrication tolerances. For this purpose, the shell compression stress shall not exceed the lowest of the following value:

Fa = 135 Fy e/D Fa ≤ 0.8 Fy (11-1)

where

Fa = allowable tension in seismic condition;

Fy = yield stress;

e = thickness;

D = shell diameter 11.8. Ground supported vertical tanks 11.8.1. The following provisions shall be applied to cylindrical or rectangular tanks, which are

symmetric with respect to a vertical axis and where their bottoms are directly supported on the ground. The tanks shall be made of steel or reinforced concrete and may contain any kind of liquid.

11.8.2. In every matter that do not contradict the provisions of these clauses, and in consonance

with the tank material and content, the use of the following standards or design recom-mendations for the design of tanks are allowed: API 650 Welded Steel Tanks for Oil Storage; API 620 Design and Construction of Large Welded Low-Pressure Storage

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Tanks; Seismic Design of Storage Tanks issued by the New Zealand National Society for Earthquake Engineering together with the New Zealand Standard 4203; AWWA-D 100 Standard for Welded Steel Tanks for Water Storage, AWWA-D 110 Wire and Strand Wound Circular, Prestressed Concrete Water Tanks, AWWA-D 115 Circular Prestressed Concrete Water Tanks with Circumferential Tendons, ACI 350.3 Practice for the Seismic Design of Liquid Containing Structures, or other internationally recognized standards, specifically accepted by the professional specialist who approves the project, in accordance with 4.4.2. In particular, the design base shear shall be calcu-lated according to clause 5, and shall not be less than the value that results from the ap-plication of provisions 11.8.6, 11.8.7 and 11.8.8. The design of each tank shall be based on only one of the previous standards avoiding to mix provisions from different stan-dards. Noteworthy is the fact that New Zealand standards consider load and resistance factors, while all others of the aforementioned standards consider allowable stresses.

11.8.3. The model of analysis shall consider both the horizontal impulsive response, in which

one portion of the content vibrates in unison with the structure, and the horizontal con-vective response associated to wave action on the free surface.

11.8.4. For the purpose of calculating the participating periods and masses associated to the

convective and impulsive modes of response, it can be assumed that the tank is in-finitely rigid.

11.8.5. The determination of the hydrodynamic masses and periods associated to the impulsive

and convective response modes shall be carried out in accordance to the specifications in the design standards detailed under 11.8.2, as appropriate.

11.8.6. For the design of steel tanks a maximum value of R = 4 of the response modification

factor shall be used. 11.8.7. For the design of reinforced concrete tanks a maximum value R = 3 of the response

modification factor shall be used. This value is applied to the normal construction of continuous connection between wall and base. If this condition is not fulfilled, lower values for R shall be used which shall be justified by the project engineer.

11.8.8. The spectral design acceleration or seismic coefficient of the impulsive mode for the

horizontal seismic action shall be equal to the maximum seismic coefficient from Table 5.7 for ξ = 0.02 in case of steel tanks, and ξ = 0.03 in case of concrete tanks. The spec-tral design acceleration or seismic coefficient of the convective mode for the horizontal seismic action shall be determined according to expression (5-2) considering a damping ratio equal to ξ = 0.005; this value in no case shall be less than 0.10 A0/g.

11.8.9. In those cases where the design standard used considers the vertical action, the vertical

seismic coefficient shall be equal to 2/3 of the impulsive mode coefficient. 11.8.10. The design shall consider the coefficients of importance according to 4.3.2.

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11.8.11. If appropriate, modal stresses and deformations shall be superposed according to the

specified in the design standard in use. 11.8.12. In those cases where load and resistance factors design methods are used, the loads shall

be combined according to 4.5. 11.8.13. In anchored metal tanks of flat bottom, the design of the anchor bolts shall be carried

out such that 1/3 of the number of the bolts are capable of taking the total seismic shear load, unless the anchorage system includes a device that warrants that 100% of the bolts are active to take the seismic shear load. The design of anchor bolts shall consider the simultaneous occurrence of tensile and shear stresses.

11.8.14. In non-anchored tanks the bottom shall be designed with a minimum conical slope of

1%. 11.8.15. To reduce the risk of spillages and for preventing failures in the roof and upper part of

the tank wall, the design shall include a freeboard between the free surface of the liquid and the structure of the roof, higher than or equal to the convective-mode wave height.

Smaller freeboards can be used, provided that the sub pressure caused by the contact be-tween the liquid and the roof were considered. This pressure shall be used for the design of the roof and its connections with the rest of the structure.

11.8.16. In order to prevent secondary damages caused by the movement of the liquid, the fol-

lowing conditions shall be fulfilled:

a) in metal tanks, the roof plates shall not be welded to the purlins; b) the normal diameter of the air vents on the roof shall be duplicated;

c) in metal tanks, the vertical displacement of the columns at the bottom shall be allowed.

11.8.17. The piping systems and their connection points to the tank shall be designed with ample

deformation capability in order to prevent the possible damages caused by eventual up-lifts of the tank bottom or tank displacements.

11.9. Rotary kilns and dryers 11.9.1. The longitudinal earthquake component shall be resisted by rims and thrust rollers in-

stalled at both sides of the rim and placed on only one support for allowing longitudinal expansions (see Appendix A, Figure A.11).

To ease the operation, a free space shall be left between the thrust rollers and the rims. The design shall consider the possibility of longitudinal impact when this space closes.

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It will be allowed to design the rollers and their mechanisms as elements substitutable, which may fail in case of earthquake. If so, the manufacturer shall promptly provide detailed repair instructions to prevent damages to the kiln in the cooling process.

11.9.2. The transversal earthquake component shall be resisted by rims and lateral rollers in-

stalled on various supports. The width of the rollers shall be greater than the width of the rims to prevent their falling due to thrust roller failure.

11.10. Refractory brick structures 11.10.1. The design of foundry furnaces and similar process equipment, composed of steel or

concrete structures combined with refractory brickwork, which are operated at high temperatures, shall be carried out trying to find configurations where the structural earthquake-resistance is provided by the conventional materials and only exception-ally by the brickwork. (An example is presented in Appendix A, Figure A.12, where the suspended roof shall be preferred).

11.10.2. When it is unavoidable that the brickwork behaves as an earthquake-resistant element,

special analyses that consider the non-linear characteristics of the material shall be employed.

11.10.3. The design shall consider the conditions of cold furnace and start up, as well as its

normal operation. 11.11. Electric equipment 11.11.1. The provisions of this standard are applicable to the structural aspects of electrical

equipment located in the interior of industrial plants. They are not applicable to power generating and transmission equipment nor to main substations, all of which shall be ruled by special specifications.

11.11.2. The electric operativity of this equipment in the course of an earthquake shall be

qualified in compliance to special standards, which shall be determined by the process engineers.

11.11.3. The electric isolators shall be designed against break with minimum safety factor of

3.0 for the loading combinations that include earthquake action. 11.12. Minor structures and equipment

Every equipment and structure independently of their size and importance shall be ca-pable of resisting the seismic loads specified in this standard and shall be appropriately anchored (see Appendix A, Figure A.13).

11.13. Wood structures

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Wood structures shall be designed in compliance to NCh1198. Connections shall fea-ture ductile behavior and failure strength in bending or tension shall be lower than that of the connected elements. The R value to be used for the design of cooling towers shall be equal to 4.

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Appendix A (Normative)

Typical details

Figure A.1 – Column base

Figure A.2 – Roof bracing

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Figure A.3 – Detail of crane beam and columns

Figure A.4 – External wall bracing

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Figure A.5 – Connection of column to masonry wall

Figure A.6 – Rigid equipment inside of building

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Figure A.7 – Typical details of large suspended equipment, seismic connectors and anchor bolts

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Figure A.7 – Typical details of large suspended equipment, seismic connectors and anchor bolts (conclusion)

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Figure A.8 – Typical details of large mobile equipment

Figure A.9 – Wheel rail system

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Figure A. 10 – Typical details of large tanks

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Figure A.11 – Typical rotary kiln and dryer details

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Figure A.12 – Typical details of industrial brickwork

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Figure A.13 – Typical details of minor structures and equipment

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Appendix B (Normative)

Design of beam to column connections in rigid steel frames

B.1. General considerations

The use of the AISC provisions for the design of rigid frames contained in the Seismic Provisions for Structural Steel Buildings 1999, is subjected to the following restrictions:

a) This standard shall be applied to the design of non-braced rigid frames without the

additional obligatory requirements of the AISC Seismic Provisions. In particular, not applicable are the AISC Seismic Provisions for special frames (paragraph 9) and intermediate frames (paragraph 10), and no laboratory testing of the connec-tions between beams and columns is required.

b) The provisions in paragraph 8.3 of this standard shall be applied to frames with

concentric bracing without the additional obligatory requirements of the AISC Seismic Provisions.

c) Frames with eccentric bracing shall be designed according to AISC Seismic Provi-

sions, paragraph 15. B.2. Design of the panel zone of moment connections B.2.1. The analysis can be made by means of elastic or plastic methods. B.2.2. The web panels shall be reinforced with web reinforcing plates or diagonal stiffeners (Fig-

ures B.1 and B.2) if the action Ru exceeds Ф Rv , where Ф = 0.75 and Ru and Rv are de-termined as follows:

a) um

u

m

uu V

dM

dMR −+=

2

2

1

1 (B-1)

where

Mu1 and Mu2 : Beam bending moments at the connection due to the load-ing combinations detailed under 4.5 b), where the seismic loading condition of these combinations has been ampli-fied by 2, but not greater than the respective plastic bend-ing moments.

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dm1 and dm2 : 0.95 d1 and 0.95 d2 , where d1 and d2 are the beam heights;

Vu : shear load in the column at the connection level due to the loading combinations detailed under 4.5 b), where the seismic loading condition of these combinations has been amplified by 2.

b) If Pu < 0.75 Py

Rv = 0.60 Fy dc tp ⎥⎥⎦

⎢⎢⎣

⎡+

pcb

cfcf

tddtb 23

1 (B-2)

c) If Pu > 0.75 Py

Rv = 0.60 Fy dc tp ⎥⎥⎦

⎢⎢⎣

⎡+

pcb

cfcf

tddtb 23

1 ⎟⎟⎠

⎞⎜⎜⎝

⎛−

y

u

PP

2.19.1 (B-3)

where

bcf = width of column flange;

tcf = thickness of column flange;

dc = height of column shape;

tp = total thickness of the panel zone including rein-forcing plates;

db = higher value between d1 and d2 (see Figure B.2);

Fy = yield stress;

Pu = axial compression load for the design of the col-umn;

Py = AFy , axial yield load of the column;

A = area of column section.

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Figure B.1 – Web reinforcing plates

asaez
Pencil
asaez
Pencil
asaez
Pencil
asaez
Pencil
asaez
Note
Reinforcing
asaez
Note
reinforcing
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Figure B.2 – Panel zone forces

asaez
Pencil
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B.2.3. The panel zone shall always be provided with continuity stiffeners (Figure B.2) designed

to resist the forces transferred by the flanges of the beam to the column. B.2.4. The reinforcing plates shall be connected to the column flange by means of fillet or com-

plete-penetration groove welds, calculated to resist the design shear forces. When at-tached to the column web, they shall be welded along their upper and lower edges. When placed apart, they shall be installed symmetrically and welded to the continuity stiffeners.

B.2.5. The thickness of the column web or of each attached plate shall satisfy the following ex-

pression:

t > (d2 + w2 ) / 90 (B-4)where

t = thickness of web or of each plate;

d2 = height of panel zone between continuity stiffeners; w2 = width of panel zone between the column flanges.

B.2.6. Field-welded connections between the beam flanges and the column shall be complete-

penetration groove welds, welded in horizontal position on backing plates with non-destructive inspection, X-ray or ultrasonic testing.

B.2.7. The backing plates and start or end weld coupons shall be removed. After their removal,

the metal shall be cleaned and the root of the weld shall be reinforced with fillet welds. B.3. Local bending of the column flange due to a tensile force perpendicular to it B.3.1. The continuity stiffeners shall be designed for a force Ru – Ø Rn, where

Ru = tensile force perpendicular to the column flange, which corresponds to the beam bending moment Mu defined under B.2.2;

Ø = 0.90;

Rn = 6.25 yff Ft 2 ;

Where:

Fyf = Yield stress of flange, Mpa;

tf = thickness of loaded column flange, mm.

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B.3.2. If the width of the beam flange is less than 0.15 b, where b is the total width of the col-

umn flange, it is not required to carry out this verification. B.3.3. If the concentrated force Ru is applied at a distance shorter than 10 tf from the column

end, the aforementioned Rn strength value shall be reduced to one-half. B.3.4. The continuity stiffeners shall be welded to the web and to the loaded flange to enable the

transmission of the load portion taken by the stiffeners to the web1). B.4. Local web yielding due to compression forces perpendicular to the flange B.4.1. Stiffeners dimensioned for a force Ru – Ø Rn , shall be installed, where:

Ru = Compression force perpendicular to the column flange (see Figure B.3) com-ing from moment Mu defined in B.2.2;

Ø = 1.0 ;

Rn shall be determined with the following expressions:

a) If the concentrated force Ru is applied at a distance from the column end that is bigger than its height “d” :

Rn = (5k + N) Fywtw (B-5)

b) If the concentrated force Ru is applied at a distance from the column end that is smaller

than or equal to “d” :

Rn = (2.5k + N) Fywtw (B-6)

where

Fyw = specified minimum yield stress of the web, MPa;

N = beam flange thickness that compresses the column web, or that of the con-nection plates of the beam flanges, mm. If N < k, then it shall be taken N = k;

k = distance from the external face of the flange up to the toe of the web fillet weld, mm;

1) The sentence load portion taken by the stiffeners is the difference between the applied load and the resistance indicated in this paragraph and the following ones for the web of the columns. Therefore, for instance, if Ru is the factored transmitted load by the beam flange to the column and Ø Rn,min , is the lowest resistance mentioned in clauses B.3 to B.6, the column stiffener shall be designed for Rn,st = Ru – Ø Rn,min ; and the required minimum stiff-ener area is Ast = Rn,st / Ø Fy,st , with Ø = 0.9. B.7 contains additional instructions for the design of stiffeners. This note is also applicable to B.3, B.5 and B.6

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tw = thickness of the column web, mm.

B.4.2. The continuity stiffeners shall be welded to the loaded flange in order to transmit the part of the load that corresponds to the stiffener, and its web weld shall be sized for the transference of the proportion of the load taken by the stiffeners (see B.7).

B.4.3. Alternatively, if reinforcing plates are required, provision B.8 rules.

Figure B.3

B.5. Web crippling due to the compression force perpendicular to the flange B.5.1. Continuity stiffeners and eventually reinforcing plates designed for a strength of Ru – Ø

Rn , shall be installed, where Ru = Compression force perpendicular to the column

flange, coming from the moment Mu of the beam, as defined under B.2.2;

Ø = 0.75;

Rn Shall be determined as follows:

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a) If the concentrated compression is applied at a distance that is bigger than or equal to d/2

from the column end:

Rn = 0.80 ( )wfywf

w ttEFtt

dNt /31

5.1

2

⎥⎥

⎢⎢

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛+ (B-7)

b) If the concentrated compression is applied at a distance that is smaller than d/2 from the

column end: For N/d < 0.2

Rn = 0.40 ( )wfywf

w ttEFtt

dNt /31

5.1

2

⎥⎥

⎢⎢

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛+ (B-8)

For N/d > 0.2

Rn = 0.40 ( )wfywf

ww ttEF

tt

dNt /2.041

5.1

2

⎥⎥

⎢⎢

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛ −+ (B-9)

The following definitions are applicable to expressions (B.7), (B.8) and (B.9):

N = Thickness of the beam flange or of the connection plate of the beam flange

d = Total height of the column shape;

tf = Thickness of the column flange;

tw = Thickness of the column web or sum of thicknesses of the web and those of the reinforcing plates.

B.5.2. The continuity stiffeners shall be welded to the loaded flange and their weld to the web

shall be calculated for the load proportion taken by the stiffeners (see B.7 and B.8). B.6. Compression buckling of web B.6.1. This section deals with a pair of opposite concentrated forces applied to both flanges in

the same section (see Figure B.4). Continuity stiffeners and reinforcing plates shall be in-stalled across the whole web height, sized for a force of Ru – Ø Rn , where:

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Ru = Compression force in the column flange;

Ø = 0.90

Rn = h

EFt yww34.2

(B-10)

Figure B.4

B.6.2. If the pair of concentrated forces to be resisted is applied at a distance that is smaller than d/2 from the element’s end, Rn shall be reduced by 50%. The transverse stiffeners shall be welded to the loaded flanges and to the web, so to transmit the load proportion taken by the stiffeners. The weld of the stiffeners to the web shall be capable of transmitting the load taken by these (see B.7). Alternatively, when web reinforcing plates are required, rules the provision under B.8.

B.7. Additional requirements for continuity stiffeners B.7.1. Diagonal or transversal stiffeners shall also meet the following requirements:

a) The width of each stiffener plus half the thickness of the column web shall not be less than one third of the column web width nor than the width of the moment connecting plate that transfer the concentrated force.

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b) The thickness of the stiffener shall not be smaller than the thickness of the flange nor than the thickness of the moment connection plate that transfers the concentrated load; nor than its width multiplied by 250/yF (Fy in Mpa).

B.7.2. The continuity stiffeners, which resist the compression forces applied to the column

flange, shall be verified as axially loaded columns with an effective buckling length of 0.75 h and a section composed of: 2 stiffeners and a web fraction with width of 25 tw for inner stiffeners and 12 tw for end stiffeners.

B.8. Additional requirements for web reinforcing plates

Web reinforcing plates shall meet the following additional requirements:

a) The thickness and size of the reinforcing plate shall provide the necessary material for equaling or exceed the strength requirements.

b) The reinforcing plate shall be welded to transfer the proportion of the total force transmit-

ted to it.

c) Reinforcing plates in panel zones of earthquake-resistant frames shall be welded to the column flanges by using complete joint-penetration groove or fillet welding, capable of developing the total shear strength of the reinforcing plate. When the reinforcing plates are installed in contact with the column web, they shall be welded along the upper and lower edges with welds capable of taking the proportion of the total force transmitted to them. When the reinforcing plates are installed not in contact with the column web, they shall be arranged in symmetric pairs with respect to the web and they shall be welded to the continuity stiffeners on the column web with welds that are capable of transmitting the proportion of the total force that corresponds to each one.

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Appendix C (Informative)

Commentaries

(Numerals refer to the corresponding numbered paragraphs of the standard)

C.1 Scope C.1.1 The special seismic standard for industrial structures that supplements the standard on

buildings was prepared in consideration of the following reasons:

a) Industrial structures seldom have the characteristics of buildings: Discrete repartition and more or less uniform mass in height, rigid horizontal diaphragms at different levels, rela-tively low eccentricity and around 5% damping.

b) The basic design philosophy is different by reason of the great importance of industry for

the countries’ economy. Therefore, it is necessary that the basic objectives of the Building Standard (NCh433, paragraph 5.1) be supplemented by minimum business interruption risks and means for expeditious inspections and repair.

c) A very important part of industrial structures are the earthquake-resistant components of

mostly large and complex process facilities, which necessarily are designed abroad by foreign manufacturers. This introduces a factor that does not exist in the case of build-ings.

d) The industrial countries, such as the United States of North America, Russia, New Zea-

land and Japan, are gradually acknowledging the necessity of special standards for indus-trial structures. In Chile, even that no standards have been established for these matters, a quite uniform and efficient seismic design practice has been developed since 1940. This standard is mainly based on Chilean practice (1, 2)1, on the Chilean building standard (3), on the standards of the North American Uniform Building Code – UBC (4) and the Struc-tural Engineers Association of California SEAOC (5), as well as on the New Zealand’s recommendations for petrochemical plants (6).

C.1.2 This standard shall be applied to industrial structures and the equipment in industrial

premises, the objective of which is the production of goods or the compliance with estab-lished purposes. In consequence, it is not applicable to elements other than the foregoing ones, most of them external, which are covered by special standards.

C.1.3 Notwithstanding the differences between this standard and NCh433, the design of build-

ing and that of industrial structures share a series of elements regarding the seismological

1 Note: References are indicated between parentheses and are included at the end of the commentary.

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aspects, their relation with other standards, methods of analysis and similar ones. There from arises the necessary complementarity’s of these two standards.

C.2 References

The national as well as foreign cited sources are listed under References. C.3 Terminology and symbols C.3.1 Terminology

This standard supplements the terminology of NCh433, paragraph 3.1 with the terms used for industrial structures and equipment. The division of loads into permanent and diverse live load types is based on Chilean established design practices. The definition professional specialist in charge of the earthquake-resistant design of in-dustrial equipment and his/her approvals is based on the established legal conditions and practice of project engineering in Chile for local as well as international projects. Also included are the definitions of process engineers as used by the standard.

C.3.2 Symbology

The symbols listed in this standard supplements that of NCh433, paragraph 3.2 with other specific symbols.

C.4 Provisions for general application C.4.1 Principles and basic assumptions C.4.1.1 The principles enunciated in this standard with minimal variations are those practiced

in Chile and in New Zealand and articulated in the North American standards (3 to 7), while supplementing NCh433, paragraph 5.1.1.

C.4.1.2 The Chilean practice as well as New Zealand’s practice, North American standards

and NCh433, paragraph 5.2, specify the elastic analysis as basic method. C.4.1.3 Chilean and New Zealand’s practices and the aforementioned North American stan-

dards also share the conditions of ductility and redundancy. C.4.1.5 It is imperative that process engineers and the professional specialist come to agree-

ments as regards to general criteria and earthquake-resistant design details. These agreements ought to be left on record on special forms and included in the specifica-tions, like the following example:

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Structure Nº Title

Category Coefficient

I *)

Analysis

R

ξ%

Reference

Notes

201 Coal hoppers C1 1.2

Dynamic 3 3 AC.502 515

202 Operating platform C2 1.0

Dynamic 4 3 BL.016 017

203 Chimney C1 1.2

Special - - BL-023 028

Design according to ASCE-75 Steel chimney liners

204 Provisory building C3 0.8

Static 5 5 AC-21001 211

*) See 4.3.1 and 4.3.2 C.4.1.6 Topographic amplification is the enhancement of the seismic accelerations that occur

in special cases and that must be analyzed by geotechnical engineers between the ad-joining valleys and hills (as observed in the Viña del Mar earthquake of 1985).

C.4.2 Specification of the seismic action

The provisions of this standard are based on earthquake-resistant designs that have a 10% probability of excedence during a 50-year return period. The criterion of the 10% exce-dence in the course of a minimum 50-year return period has been adopted by the North American UBC and the SEOAC standards as well as by the Chilean NCh433. The 50-year return period corresponds to the service life of most buildings and industries. However, there are certain industries, such as those of the petrochemical and the mining sector, which apply a shorter service life on account of technological obsolescence or depletion of raw material sources. New Zealand’s standards for the petrochemical industry are based on a 15% excedence and 25 years of service life (6). According to these standards (6, Table 2.3 and Figure C.2.1.1), the shortening of the 50-year return period to 30 years with 10% excedence only reduces seismic stresses by 12%. This justifies the mainte-nance of the 50-year return period in Chilean standards for industry.

a) The maximum effective seismic acceleration Ao was originally defined by the U.S. Ap-

plied Technology Council ATC (7) and adopted by SEAOC and the UBS (4 and 5) as

Ao = Sa / 2.5 Where Sa is the mean acceleration of the elastic response spectrum with 5% damping be-tween periods 0.1s and 0.5s.

b) The provisions were taken from the UBC and the SEAOC (4 and 5).

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c) The totality of the Chilean coast, classified as seismic zone 3 of high intensity, is subject

to the hazards of tsunamis, which historically have reached degree 3 of the Imamura scale and in some cases a maximum degree 4 (8). The areas that feature the highest risk are Ta-rapacá, Atacama, Concepción and Valdivia. The tsunami hazard also depends on the seis-mic aspects of the coastal maritime and topographic conditions.

C.4.3 Classification of structures and equipment according to their importance C.4.3.1 The classification is based on the Chilean practice, which in the main corresponds to

New Zealand’s recommendations (6). C.4.3.2 Importance coefficients are based on the Chilean practice and on UBC and SEAOC

experience as well as and New Zealand’s recommendations, as follows:

Categories Critical C1

Normal C2

Secondary C3

Chilean industrial practice 1.2 to 1.3 1.0 1.00 NCh433 Buildings 1.20 1.0 0.60 UBC and SEAOC 1.25 1.0 1.00 New Zealand 1.30 1.0 0.83

C.4.4 Coordination with other standards C.4.4.1 Standard NCh433, paragraph 5.3 covers the Chilean standards for loads and materials. C.4.4.2 However, industrial design in Chile implies the use of a significant number of as yet not

normalized materials and loads, by reason of which it is allowed that renowned interna-tional standards be used. The most used ones in Chile are:

- American Society of State Highway and transportation Officials – AASHTO, for

bridges; - American Society for Mechanical Engineers – ASME for boilers and pressure vessels; - American National Standards Institute – ANSI/ASME for piping; - American Petroleum Institute – API for tanks for oil storage; - American Society for Testing Materials – ASTM for materials; - American Welding Society – AWS for welding - German DIN, British BS, French NF, Japanese JIS and Euro standards.

C.4.5 Load combinations

The criteria concerning load combinations are those of the American National Standard Association and of the American Society of Civil Engineers ANSI-ASCE (9), adopted by

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the American Institute of Steel Construction (10, 11) and the American Concrete Institute (12). This paragraph does not include wind loads or snow live loads, for which shall be consid-ered the design specifications that correspond to each case and the abovementioned stan-dards. In the main, wind loads can be considered a substitutive although not coincident with seismic loads in the respective formulas. Snow can be considered to be a live load that can be normal or eventual. The source of factor b = 1.4 for concrete structures or equipment is the load factor estab-lished by NCh433.Of1996 and the load and resistance factors of the ACI Code 318-99; in consequence, factor b = 1.4 shall be considered jointly with the resistance-reduction fac-tors of that ACI 318 edition. The 2002 ACI 318 edition adopts ASCE load factors, considering a factor 1.0 for the seismic action amplification, and modifies the resistance reduction factors of previous ACI 318 editions with the purpose of maintaining equivalent safety levels in the design. The load and resistance factors used until de 1999 edition are reproduced in the ACI 318-02 as alternative procedure.

C.4.6 Project and revision of the seismic design C.4.6.1 Under Chilean law all construction project designs shall be made by legally certified

professionals to work in the country. In addition, it is mandatory that structural designs of any kind of buildings be reviewed. These provisions have been supplemented by:

- The additional requirement that the professional specialist has to be a specialist in

structural engineering; - Allowing equipment designs made by foreign equipment manufacturers based on

practical reasons. However, in case of important equipment, such as large boilers, high process vessels and similar facilities, it is recommended that the foreign manu-facturer be assisted by professional specialists registered in Chile.

C.4.6.2 The approval of the design by other professionals is a prerequisite put in force in most

of the world’s Codes and Regulations (13). The standard recommends the approval of peers who shall be professional specialists registered in Chile. This recommendation is particularly important for equipment designed abroad.

C.4.6.3 The submission of drawings and calculation sheets under NCh433, paragraph 5.11, has

been simplified for a great number of minor equipment and structures destined to indus-tries in which the seismic factor is not decisive.

C.5 Seismic analysis

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C.5.1 General provisions C.5.1.1 Direction of the earthquake action

The use of horizontal actions in two perpendicular directions has been sanctioned for practice in all seismic standards. The criteria for application of the vertical component of the earthquake are based on the Chilean practice (1), New Zealand’s recommendations (6), NCh433, paragraph 5.8.2 and U.S. standards (3, 4). Vertical accelerations of 2/3 parts of the horizontals are accepted by the aforementioned standards, based on actual earthquake records.

C.5.1.3 Seismic mass or the structural model

The design earthquake is an event that occurs once or twice in the life of the industry and it lasts at the most a couple of minutes. The prerequisite for the selection of the probable live load at that moment is a clear understanding of the industry’s operating requirements. It is recommended that the seismic load be jointly determined with the operators or proc-ess engineers and the professional specialist and that the result be placed on drawings and calculation sheets.

C.5.2 Methods of analysis C.5.2.1 General

Most seismic standards, including NCh433, the North American and New Zealand’s stan-dards are based on elastic response spectra for accelerations with 5% damping, a repre-sentative value for buildings. However, industrial structures feature a 2% damping value, which is based on Chilean practice. The 2% damping was recommended by J.A. Blume and other researchers as a result of extended studies at the Huachipato Steel Plant in the wake of the severe May 1960 earthquakes in southern Chile (14).

C.5.2.2 Linear methods

a) Static analysis: Static analysis is a theoretically approached method that is applicable to structural mathematical models with uniformly distributed discrete masses in height and similar stiffness between different levels. The standard NCh433 paragraph 6.2.1, the UBC and SEAOC include criteria for determining application limits of static analysis of build-ings, which are not applicable to industrial structures. New Zealand’s recommendations limit static analysis to structures in which mass and stiffness at no matter which level have lower than 30% differences with respect to its adjacent levels.

This method should not be applied to over 20 m high buildings or structures, industrial steel buildings of more than 6 levels, over 18 m high concrete buildings, or structures with irregular configurations in plan area or elevation.

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b) Spectral or dynamic modal analysis: The dynamic analysis is applied to structures with

valid basic hypotheses of linear response, ductile behavior and viscous damping.

Dynamic analysis can be applied where static analysis is not applicable, particular in such cases as buildings and structures that support heavy hanging equipment, steel or concrete chimneys with refractory coating, and process vessels of over 20 m high or that feature a ratio height to smaller transverse dimension of over 5.

C.5.2.3 Non-linear methods

Non-linear methods are required only for structures with important variations respect to the basic hypotheses. Typical examples are large rolling equipment subject to up-lift or impact on supports, industrial masonry work that does not admit tensions, structures with base isolation and similar situations. The corresponding provisions are based on the UBC (4) and the IBC (15).

In industrial project specifications, it is advisable that the professional specialists deter-mine the method of analysis of each structure or equipment (see C.4.1.5).

C.5.3 Static elastic analysis C.5.3.1 Mathematical model of the structure C.5.3.1.3. In three-dimensional models each node has 6 degrees-of-freedom, 3 translational and

3 rotational degrees. The allocation of discrete masses to nodes is in part automati-cally appointed by the analysis programs, which provide each node with one half of the weight that corresponds to the self-weight of the node elements or elements, and in part is decided by the design engineer, who assigns to some or all model nodes the masses that are representative of the external loads or structure supported equipment. In such a way, the degree-of-freedom of each node is associated to the inertial charac-teristics of its allotted mass. The rotational inertia effects on the structural member masses are normally ignored at the moment of establishing their inertial characteris-tics, considering only their spatial 3-D translational inertia. On the contrary, the global rotation inertia effect of all masses is well represented by the spatial distribution of the total mass into a great number of nodes. When the assignation of masses to a node made by the design engineer shall represent the dynamic behavior of a body that fea-tures not ignorable rotational inertia, that mass shall be provided with the rotational inertia of the body it represents. Or else, that body can be represented by the sum of masses with purely translational characteristics, distributed and linked to each other in such a way that the joint response of all reflects the inertial characteristics of the rep-resented body. All three-dimensional analysis programs demand that the design engi-neer specifies the translational inertia as well as rotational properties of the masses considered in the model.

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C.5.3.1.4. In structures with rigid diaphragms, the masses that correspond to all nodes linked by the rigid diaphragm as well as their inertia characteristics can be condensed at the mass center and be represented by the resulting single mass that features translational inertia in both directions of the diaphragm plane and rotary inertia on the same plane, which corresponds to the distribution of the masses within the diaphragm. This con-densation greatly simplified the analysis. However, the diaphragm normally has not much stiffness in perpendicular direction in relation to its plane. Therefore, the verti-cal earthquake effects are not well represented in the foregoing simplification. In this case, the vertical earthquake component shall be treated as a case of independent load. Or else, the normal distribution of masses can be applied to three-dimensional analy-ses, and use the option of link and interdependency of the degree-of-freedom of the diaphragm nodes (constraint) for displacements within the diaphragm plane. This op-tion provides reduction in computational terms as well as the possibility of a simulta-neous analysis of the horizontal and vertical earthquake.

C.5.3.1.5. When structure supported equipment has stiffness or inertia characteristics that local

or globally can determine the structure’s response, the model shall include the repre-sentative equipment elements, which are linked to the structure the same as the equipment, having the same stiffness and mass characteristics of the actual equipment. This is the case, for instance, of large diameter ducts tied to the structure at different levels; or large vessels that are supported on several frames and/or levels of the struc-ture. Likewise, when the response of a certain structure-supported equipment must be obtained, although its translational and rotary inertia is low in relation to the level where it is located, the model shall include elements and masses that are representa-tive of the equipment and be linked to the structure the same as the actual equipment.

C.5.3.2 Horizontal base shear

The formula (5-1) coincides with the formula (6-1) of the NCh433 and has the same UBC and SEAOC format.

C.5.3.3 Horizontal seismic coefficient

The Chilean seismic design practice of industries is based on the empiric elastic response spectrum proposed by J.A. Blume in 1963 (14), after analyzing 16 structures of the Huachipato Steel Plant. Most structures were steel stacks, inverted pendulum tanks and process vessels. Seven of these structures were not damaged by the May 1960 earth-quake, while the other nine only resulted with simple damages, such as elongation of an-chor bolts and buckling of shells. Figure C-1 shows the Blume spectrum, which according to the author is reliable in the period range of 0.8 to 1.1 s and has a damping of approxi-mately 1% to 2%.

Based on Blume’s studies and long professional experience, Prof. Rodrigo Flores Alvarez proposed the following seismic coefficients (16):

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C = sforTT

115.0≤

C = sforTT

115.0≥

Cmax = 0.30 Cmin = 0.10.

The standard NCh433 (3) is based on the analysis of an appreciable number of subductive earthquakes recorded in Japan and in the 3 March 1985 Chilean earthquake (17). The elastic response spectrum proposed by the NCh433 standard with 5% damping is as fol-lows:

Q = CIP

C = 2.75 n

TT

gRA

⎟⎠⎞

⎜⎝⎛ '0

(formula 6-1 NCh433) (formula 6-2 NCh433)

where T’ and n are parameters that depend from the soil.

This standard proposes the formula format (6-2) with a coefficient that enables the con-sideration of damping ratios other than 5%.

C = 2.75 n

TT

gRA

⎟⎠⎞

⎜⎝⎛ '0

4.005.0

⎟⎟⎠

⎞⎜⎜⎝

⎛ξ

Figure C.1 shows the foregoing spectra of the Huachipato Plant, zone 3 and soil type II of NCh433 Table 4.2. It also shows Blume’s empiric spectrum as well as those of UBC 93 and SEAOC 92. Worth mentioning is that the coincidence is satisfactory.

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Figure C.1 – Huachipato response spectra (Zone 3 A0 = 0.4 g Soil type II I = 1.0)

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Soil parameters

The soil classification and parameters of Table 5.3 and 5.4 are taken from NCh433, Ta-bles 4.2 and 6.3.

Values of damping and R coefficient

The determination of the values of damping and the structural modification factor R of Tables 5.5 and 5.6 are a result of the study of many actual cases of structures on every soil type and seismic zone, subject to the severe earthquakes of 1960 and 1985, as well as of comparative analyses with the UBC and SEAOC standards.

C.5.3.3.1. and C.5.3.3.2 Limit values of the seismic coefficient

The following table shows the maximum and minimum values of the seismic coefficient of several standards and the Chilean practice for I= 1.

Maximum Minimum ReferenceChilean practice, industries, zone 3 – soil II 0.35 g 0.10 g NCh433, buildings, zone 3 0.24 g 0.067 g 3 UBC-SEAOC, industries, zone 4 0.367 g 0.20 g 4, 5 UBC-SEAOC, buildings, zone 4 0.275 g 0.075 g 4, 5 NCh2369, zone 3 – soil II, R = 3, ξ = 0.03 0.34 g 0.10 g

The values of the Chilean practice are within the range of the other standards and have been proved to be effective in 5 severe earthquakes of magnitudes between 7.5 and 9.5, in the years 1960 to 1985.

C.5.3.5 Height distribution

The proposed formulas are NCh433 (3) (6.4) and (6-5).

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Figure C.2 – Huachipato Plant design spectra (Zone 3 A0 = 0.4 g Soil type II I = 1.0)

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C.5.4 Dynamic elastic analysis C.5.4.2 Design spectrum

See C.5.3.3. C.5.4.3 Number of modes

The condition of taking enough modes for achieving 90% of the total mass is part of NCh433, UBC, SEAOC standards and the New Zealand’s recommendations (3, 4, 5, 6).

C.5.4.4 Mode superposition

The complete quadratic superposition and proposed formulas are from NCh433, para-graph 6.3.5.2.

C.5.4.5 Minimum base shear

See C.5.3.3.2. C.5.4.6 Torsion in plan

Recommendations are based on the Chilean practice. C.5.5 Vertical earthquake action

The necessity of considering the vertical earthquake action is justified under C.5.1.1. The provisions shall be applied to the structural provisions described in 5.1.1.a), b), c), d) and e), where the seismic forces have special importance and have caused damage due to earthquakes.

C.5.6 Robust and rigid equipment resting on floors

This mostly very stiff equipment prevails in industry. This provision is based on SEAC and UBC 1997 recommendations.

C.5.8 Special analyses

Special analyses are applied in cases where the basic hypotheses of the linear analyses de-scribed under 5.2.2 are not fulfilled. The standard differentiates two basic procedures, spectral and time-history analysis.

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The spectral analysis is based on the preparation of spectra that consider the non-linearity of the structural response, taking in to account the maximum values of the seismic factors instead of site and type of soil. The time-history analysis is based on a step-by-step analysis of the structural response for at least 3 historical records or one synthetic record. The provisions are based on local studies that consider the provisions of New Zealand and North American UBC standards as well as SEAOC standards.

C.5.9 Structures with seismic isolation or energy dissipation devices

The provisions for seismic isolators are based on UBC 97 with minor modifications. For further details see reference 19.

C.6 Seismic deformations C.6.1 Calculation of deformations

The formula (6-1) initially proposed in ATC-3 has been adopted by UBC, SEAOC and the New Zealand’s recommendations (4, 5, 6, 7), which is an acknowledgement of the fact that the reduction of stresses from an elastic response spectrum to that of a design spectrum cannot be applied to deformations.

C.6.2 The separation s = d1 +d2 contained in New Zealand’s recommendations (6) is conserva-

tive, because d1 +d2 almost never occurs at the same moment. The Chilean practice often uses the expression s = 2

221 dd + , that is more probable but lacks a safety margin. Chile

has been applying the values 0.004 h and 30 mm. C.6.3 Chilean practice in general has not limited horizontal seismic deformations in industrial

structures, except where they could damage elements joined to the structure, such as pip-ing and ducts. The UBC and SEAOC standards contain the limitation 0.04 h/R; observed deformations in the May 1960 earthquake were of h/75 = 0.0133 in industrial buildings with overhead traveling cranes (6), similar to the proposed formula.

C.6.4 The P-Delta effect very seldom has importance in industrial structures but could be im-

portant in rigid frame structures. C.7 Secondary elements and equipment mounted on structures C.7.1 Scope

Clause 8 of NCh433, based on ATC-3 (7) mainly deals with the secondary elements of buildings. The basic theory has been maintained in this clause, although with some minor industry-oriented modifications.

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C.7.2 Forces for seismic design

Formulas (7-1) to (7-6) and Table 7.1 correspond to an improved version of NCh433, clause 8.

C.7.3 Forces for anchoring design

One of the most frequent causes of seismic failure in minor equipment is the lack or insuf-ficiency of anchorages as a result of the application of normal practice in non-seismic zones. Anchor bolts meet the need of most equipment that does not require special devices, such as shear plates.

C.7.4 Automatic shutoff systems

This recommendation was derived from NCh433, paragraph 8.5.4. C.8 Special provisions for steel structures C.8.1 General provisions

The special provisions are based on the Chilean practice and on North American recom-mendations, which were prepared after the Loma Prieta and Northridge seisms and after-wards introduced in their standards. The Chilean experience has been proved in six severe seisms of Richter Kamamori mag-nitudes 7.5 to 9.5, between 1960 and 1985. The North American Standards were summarized in the AISC earthquake-resistance de-sign standards and recommendations (10, 11 and 20). Recommendations from AISI (21) for slender elements, not included in AISC, were also considered.

C.8.2 Materials

The purpose of steel and welding specifications in North American Standards (4, 5, 15) has the purpose of preventing fragile fracture failures. They are based on numerous stud-ies prepared after the Loma Prieta and Northridge earthquakes. Some fragile fractures in high strength, low toughness steels have been observed in bridges under non-seismic con-ditions.

C.8.3 Braced frames

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The recommendations on bracing are based on the Chilean experience, with some modifi-cations from AISC. The maximum seismic deformation of our standards has been gener-ally considered to reach approximately half of the value used in the United States, which reduces the risks of failure due to local or anelastic buckling. Provision 8.3.2 on the use of braces that take compression and tension, has been taken from Euro standards; its purpose is to increase redundancy [see 4.1.3.b)]. Provision 8.3.4 on the point of the intersection of the braces, not considered in North American standards, has been permanently successful in Chile; it was based originally on Austrian standards. The Chilean practice derived from the North American guide (22) habitually uses as minimum height 1/90 of the horizontal projection of the sections of the braces in order to prevent deformations due to self-weight, which reduces the buckling strength.

C.8.4 Rigid frames

Structures exclusively based on rigid frames as habitually used in the United States, pre-sented many failures in beam-column connections during the Loma Prieta and Northridge earthquakes, giving rise to ample research and, as a result, the strict design requirements included in the main seismic standards (5, 15). These were summarized in AISC recom-mendations (20). In Chile there were no failures in these joints, thanks to the lesser seis-mic deformation and the avoidance of rolled heavy-duty jumbo sections that feature a dangerous metallography. This is the reason why the proposed provisions are based on our experiences and very few AISC recommendations. Provision 8.4.1 specifies totally rigid TR beam-column moment joints. Partially rigid or PR joints allowed in the United States are not accepted based on two reasons: Lack of lo-cal experience and the requirement of tests and studies, which are not available in Chile. Paragraph 8.4.3 and Table 8.1 that specify width to thickness ratios were taken from AISC seismic design recommendations (10, 11 and 20), with some corrections based on local practice. 8.4.5 and Appendix B include provisions for the design of the column panel zone in rigid connections to beams, based on AISC non-seismic recommendations (10) with very few modifications from the earthquake-resistance design recommendations (20). No panel zone failures have been observed in Chile. 8.4.6 recommends provisions for column bases, detailed in 8.6.2, with a view to post-seism inspection and repair of an-chor bolts.

C.8.5 Connections

All provisions are based on local practice and AISC recommendations. The standard un-der 8.5.2 and 8.5.3 specifies the design of seismic connections for a resistance that is

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higher than or equal to that of the connected elements, while 8.5.8 includes the require-ments for executing reliable field-welded connections. Column joints (see 8.5.9) shall be designed with a 5 kN horizontal force sited in the free upper end during the mounting.

C.8.6 Anchorages

Foundation anchorages usually present failures during earthquakes that are minor in gen-eral. They might be called “seismic fuses”. The provisions offered in 8.6.2 have the purpose of expediting post-earthquake inspec-tions and repairs. They are based on the local experience that primarily considers the fail-ures observed in 1960, which could be prevented in later seisms. The use of shear plates or seismic bumpers mentioned under 8.5.3 to 8.6.7, like in the foregoing case, is based on the failures that were detected in 1960 and the successful be-havior of the abovementioned recommendations afterwards. Paragraph 8.6.5 excludes the friction between base plate and foundation mainly due to the setting contraction of the leveling mortar. Friction can be taken into account in special cases, mainly large equipment with many anchorages, where non-shrinkable mortar and prestressed bolts shall be specified and usually only prestressing is considered for friction. The recommendation of 8.6.8 to prevent anchorage failures ascribable to the concrete is a habitual protective measure against the difficulty of obtaining reliable concrete and the uncertainties of the resistance calculation theories. In general, it is recommended that the design of the Prestressed Concrete Institute PCI (23) be applied.

C.9 Special provisions for concrete structures C.9.1 Reinforced concrete structures

In the main, standards are based on the local seismic experience from 1960 to 1985, the provisions of NCh433 and the recommendations of the American Concrete Institute ACI-318-99, chapter 21 (12), and also the post-Loma Prieta and Northridge research works, published by the Earthquake Engineering Research Institute (24), chiefly regarding pre-casted elements where local experience is limited. NCh2369, 9.1.6 specifies that it is not necessary that seismic walls be designed according to the complex ACI provisions. Our designs in which these are not applied have been successful since the 1960 earthquakes, fact that is acknowledged at international level.

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The provisions of 9.1.7 for rigid frames that eliminate ACI requirements are justified be-cause of the lesser seismic deformation of this standard and from several numerical stud-ies. There is a commented translation of the ACI 318 code done by a Structural Design Com-mission for reinforced concrete and masonry and by the Chilean Institute of Cement and Concrete. This has been proposed by its authors as Chilean Code for the Design of Rein-forced Concrete Design.

C.9.2 Precasted concrete structures

The provisions consider the limited Chilean experience regarding the seismic behavior of precasted elements, the requirements of ACI 318-02 and IBC 2000, as well as the propos-als contained in NEHRP 2000, centered on the prevention of these systems’ failures ob-served in the Loma Prieto, Northridge and Kobe seisms (12 and 24).

C.9.2.1.1 a) and b) accept the design of gravitational systems with wet seismic joints as an equivalent of traditional concrete, because the precasted structure must be of better quality than field-prepared concrete and joints are equivalent. Added special restrictions of structures with dry connections are based on the limited lo-cal experience with this type of structure. 9.2.1.1 c) limits the height of structures to 18 m and the number of building stories to 4, which are the maximum values used by local pro-jects. Provisions 9.2.1.1 c), 9.2.1.4 and 9.2.1.5 demand that the design prevents the failure of dry connections before those of the structural element and that tests must prove the behav-ior in case of non-linearity.

C.9.2.1.6 stipulates that the requirements of steel and welds of dry connections be the same as those specified under 8.2.2 and 8.5.1 in order to prevent fragile failures. Finally, 9.2.1.7 specifies design conditions for very low seismic stresses; these are similar albeit stricter than those specified under 5.4.5 for non-precasted structures.

C.9.3 Industrial bays composed of columns in cantilever

The design of columns and foundations including stresses and deformations, shall allow for the model-assigned base shear in addition to vertical earthquake action. However, when the horizontal bracing system imposed by 9.3.2 has been conceived for providing structural redundance, the base design shear shall not be less than the value that results from multiplying the weight that the column transfer by the highest value between C and Cmin.

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C.10 Foundations C.10.1 These specifications are based on the extensive Chilean experience regarding founda-

tions of buildings compliant to NCh433 and decades of projects for the large-scale min-ing sector and a wide range of different industries.

C.10.1.3 This paragraph shall be construed as the requirement that tensions in the soil, its de-

formation and the stability of the foundation shall be verified in all applicable combi-nations by means of the method of allowable tensions, that result compatible with the principles of soil mechanics.

C.11 Specific structures C.11.1.1 Industrial mill buildings C.11.1.2 Commonly used in industry because of their expansion possibilities are mill buildings

in which lateral forces are resisted by the stiff frames of columns and beams or roof trusses.

The continuous roof bracing has the seismic advantages of stiff horizontal dia-phragms. In addition, it enables the distribution of concentrated lateral loads between several frames, as is the case of cranes. The Chilean US-based practice considers sat-isfactorily approximate the assumption that the roof bracing transmits 50% of the lat-eral load to the frames that adjoin the loaded one.

C.11.1.3 The determination of the magnitude and height of the suspended load that matches the

design seism is a complex probabilistic problem, which ought to be jointly analyzed by the professional specialists and process engineers. However, considering the short duration of the seismic forces as compared to the service life of the structure, the fol-lowing recommendations ought to be considered as being safe:

- In cranes of maintenance, fabrication and similar workshops, which seldom hoist the

maximum load and where operations are discontinuous, the suspended load can be ig-nored in the seismic analysis.

- The seismic analysis of cranes for heavy and continuous operations with maximum

load, such as those of metallurgical foundry shops, ought to use this load at its highest level. This recommendation is based on the dynamic analysis of over 600 cases, per-formed in Chile (25), according to which the load equivalent to bridge level matches the actual one for pseudo-periods of 1 s or more, and to 0.20 of the actual one for pe-riods of up to 0.5 s, linearly varying between both values.

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The following figures summarize the conclusions of abovementioned study.

Ts = ))((2 21 kgPP +π pseudo period P1 = Weight of building, bridge and crane carriage P2 = Weight of the suspended load

mP2 = Suspended load of analysis applied at upper level K = Stiffness Ts < 0.5 m = 0.20 Ts = 0.5 – 1.0 m = 1.6 Ts = 0.6 Ts > 1.0 m = 1.0

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C.11.1.4 The non-simultaneity of seism and the operating cranes’ dynamic effects and the posi-

tion of several cranes without load is justified by probabilistic reasons and is part of the North American practice recommended by the Association of Iron and Steel Engi-neers – AISE (22).

C.11.1.5 The May 1960 seisms caused systematic failures in the vertical plate joints between

the crane supporting beam and the columns on account of the superposition of seismic stresses and fatigue stresses. There also were cases of wheels falling from the rail to the upper flange of the crane beam. The recommendations have the purpose of pre-venting such failures (1, 26, 27).

C.11.1.6 This provision is intended to prevent the construction of stiff towers at the end fa-

cades, which failed during Chilean earthquakes, on account of taking in seismic forces for which they had not been designed (27).

C.11.1.7 The advice is self-explanatory. According to the Chilean practice the recommended

detail has had satisfactory results. C.11.2 Light steel bays C.11.2.1 This paragraph defines the characteristics of light steel bays (mills), limited clearances

and height and low-weight cranes and equipment, where wind loads really are higher than the seismic loads. In the course of the years a great number of such bays has been built, which do not meet all the requirements of this standard but have resisted seisms without damages.

C.11.2.2 This paragraph defines the parameters required for the determination of the seismic

design forces. In general, the transverse and longitudinal wind forces at the end pan-els are higher than the seismic forces, but in intermediate panels the controlling force can be the longitudinal seismic force.

C.11.2.3 to C.11.2.7 These are bracing design provisions. Where no cranes or equipment of

equivalent weight are involved, exclusively tension braces are allowable. C.11.3 Multi-story industrial buildings C.11.3.1 Most multi-story industrial process, energy generating and similar buildings, supports

heavy loads and valuable equipment. The best results achieved by the Chilean prac-tice are dual buildings, with braced shear or concrete walls in combination with rigid ductile frames as second resistance line (1, 26, 16). These buildings feature much lower seismic deformations than those with North American ductile frames; they have

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not been subject to the generalized welded joint failures that occurred in the North-ridge seism of 1994 (28, 29, 30, 31).

C.11.3.2 These recommendations are based on the Chilean practice proved after the 1960 to

1985 seisms (1, 16, 26, 27, 28). C.11.4 Large suspended equipment C.11.4.1 Figure A.7 of Appendix A illustrates a typical boiler suspended from stay bolts at its

upper end. The control of seismic oscillations and prevention of impacts with the structure requires connectors that allow horizontal as well as vertical thermal expan-sion (see Figure). The same Figure shows the hammerhead anchor bolts, made for ample ductility and being readily repairable and replaceable are recommended for large equipment.

Such equipment is usually projected by foreign manufacturers who frequently have no seismic experience. Therefore, early assistance systems must be set up accompanied by the design approval of specialized professionals licensed in Chile. The foregoing recommendations have been successfully proved in a series of seisms since 1960 in Chile (1, 16, 32).

C.11.4.2 Parts of electrostatic precipitators are the very high voltage electrode cages, which are

suspended from isolators and as they cannot be gripped laterally they may impact the shell in case of seism. Chilean practice has observed that such impacts are not signifi-cant but present electric problems and fragile rupture of the porcelain isolators. In consequence, it is frequently necessary that special isolators are specified and that power supply deactivating devices be implemented.

C.11.5 Piping and ducts C.11.5.1 The layout of supports and connections shall be made jointly by pipe laying specialists

and the professional specialists. C.11.5.2 In general the seismic action shall be considered in case of piping or ducts of over 200

mm. The weight of tubes is mostly insubstantial as compared to the weight of build-ings and structures; therefore it is enough that the seismic deformations be considered in the analysis of the piping system and in the design of the connections.

C.11.6 Large mobile equipment C.11.6.1 Large mobile equipments are particularly important in an industry, in consideration of

their high cost and because their failure can lead to protracted standstills. Mostly large-sized, such equipment often features highly eccentric loads. Seismic design is

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therefore critical and requires that throughout the project appropriate coordination and approval systems be set up between suppliers and seismic engineering specialists.

The design, considering the actual support between wheels and rails, with the likeli-hood of crashing and rising, has uncertainties, which in practice make it impossible. Therefore, usually these supports are assumed to be pin connections for analysis pur-poses, and precautionary measures are taken to prevent impacts by means of counter-weights and self-centering wheels. Above provisions have been successful in Chilean practice. Most equipment pro-tected in such a way has not presented failures, except a few cases of successive bangs that caused repairable damages to wheels and cars (26, 27). The design of counter-weights usually considers a pseudo-static safety factor of approximately 1.0 to 1.2 in static analyses. The dynamic analysis shall provide for vertical and horizontal accelerations, while probable live loads during the occurrence of a seism shall be determined jointly with the operators. Total capsizing due to seismic action is not a real possibility, because of the alternat-ing loads and thus shall not be considering in the design (33, 34). During the Chilean seisms of May 1960 and March 1985 portal cranes turned over in the Puerto Montt and San Antonio seaports, but these were ascribed to soil settlements and not to hori-zontal seismic forces (29, 35).

C.11.7 Elevated tanks, process vessels and steel chimneys C.11.7.1 Elevated tanks shall be designed as inverted pendulums with R = 3. Water in general

can be considered as a solid 0.8 times its weight (35). Where exclusively X tension braces are used, pretensioning equal to half of the maximum tension of the tensioned brace must be applied.

C.11.7.2 The dynamic analysis of process vessels shall be made with R = 3. The connection

between columns and shell may be direct if the plate is thick or by means of a circular support beam. The design of these connections is complex and could be made by the methods developed by Brownell and Young (37).

C.11.7.3 Chimneys can be self-supporting or not self-supporting with a metal or concrete ex-

ternal structure. These latter ones are used for stacks of thermal power plants. The Chilean experience has been successful with stacks of up to 53 m, based on the dy-namic designs according to paragraph 5.4 of this standard and R = 3. Higher non self-supporting stacks of up to 500 m have been designed according to the conserva-tive method recommended by the American Society of Civil Engineers (27, 38). The recommendation of using interior concrete grouting for calculating stiffness but not for resistance is based on the studies of Blume on the effects of the 1960 seism on the

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Huachipato Steel Plant (14). Blume recommends that the coating be assigned the value E of 1/20 steel.

C.11.7.4 Formula (11-1) is based on the Timoshenko expressions reviewed by Blume based on

his observations of the behavior of 12 Huachipato Steel Plant chimneys of between 33 and 52 m height, 3 of which presented local buckling failures in the May 1960 earth-quakes. The recommended failure tension that considers fabrication and mounting de-fects is as follows:

Fu = 170 Fy e / D

The acceptable value when applying allowable tensions is

0.6 x 1.33 Fu = 0.8 Fu

that is equivalent to formula (11-1).

Fa = 135 Fy e / D less than 0.8 Fy

According to paragraphs 4.5 and 8.1.b) when applying ultimate loads, the seismic stresses shall be multiplied by 1.1 accepting that

Fa = 153 Fy e / D less than 0.9Fy.

C.11.8 Ground supported vertical storage tanks C.11.8.1 Scope

Industry is the major user of large ground supported storage tanks, most of which are circular steel tanks, although some few are of reinforced concrete or of rectangular shape. The most frequently stored fluids are oil, water, and other special ones such as sulfuric acid, liquefied oxygen, alcohol, etc.

C.11.8.2 General principles and standards

Most design engineers apply the North American design and construction standards issued by the American Petroleum Institute – API in case of petroleum products stor-age structures, and for designing water storage structures those of the American Wa-terworks Association – AWWA and of the American Concrete Institute – ACI (39, 40, 41 and 42). Also used are the recommendations of the New Zealand National Society for Earthquake Engineers – NZ, which are applicable to any fluid and material. Origi-nally issued in 1986, these specifications are very exhaustive; having been considered too conservative, they were modified in 2000 (43, 44).

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Every standard contains two important sections: Seismic Considerations, where seis-mic stresses are determined: location, risk and required safety; and Design that en-ables the dimensioning of tanks and their foundations. This standard specifies seismic action conforming to Chilean conditions that differ from those of API, AWWA or NZ. Knowing the seismic forces, the design follows one of the abovementioned standards. This is the same philosophy applied in the United States (45).

C.11.8.3 to 11.8.5 Masses and periods

The design shall consider that the fluid mass is broken into two forces: the impulsive force that vibrates in unison with the structure, and above it, the convective one that features waves. The three standards referenced under 11.8.2 have practically coinci-dent formulas for determining the masses and periods of each one of these forces.

C.11.8.6 to 11.8.13 Analysis and design

The determination of the seismic stresses and of the structural parameter R as well as damping ξ is based on a comparative study of eight steel and two concrete tanks of sufficient dimensions for covering the practice requirements; results were compared with the values of the standards mentioned under 11.8.2. The relations between the seismic coefficients of the 10 tanks were the following ones:

NCh2369/API 1.01 to 1.17 NCh/AWWA 0.80 to 0.90 NCh/NZ 0.96 to 1.00 C.11.8.14 Anchor bolts

The provisions for anchor bolts have been successfully applied in Chilean projects in the course of the last decades.

C.11.8.15 to C.11.8.18 The standard specifies methods for preventing that tank without anchor

bolts slip out of their foundations, that the roof be damaged by air compression or by the impact of the convective fluid or secondary problems in the structure and piping.

The recommendations are based on the Alaska 1964 seism damages, on those caused by the Chilean seisms of 1960 and 1985, as well as on the recommendations provided on each of these occurrences (1, 27, 28, 46, 47, 48, 49 and 50).

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C.11.9 Rotary kilns and dryers C.11.9.1 Rotary kilns and dryers can be facilities of large diameter and length; they are oper-

ated at high temperatures and low rotary velocity. Foundations are massive and natu-ral periods are low, which justifies the use of the static method.

Rotary kilns and dryers feature an appreciable longitudinal and radial thermal expan-sion. Rotating outages during a period of around 20 minutes can cause thermal expan-sion and considerable damages. These restraints carry weight in the design, which re-quires an early and continuous cooperation between the equipment manufacturer and the professional specialists. The recommendations of this standard have been successfully proved in a great num-ber of kilns and dryers installed in Chile since the 1940’s (26). Experience shows that the impact with the closure of the free space in the longitudinal seism may double the seismic force (51) and that this can be several times larger than during normal operation. Therefore, operators must necessarily accept occasional re-placements of rollers and roller mechanisms, provided these are promptly replaced with a procedure of controlled furnace rotation to prevent important thermal deforma-tions. This procedure requires a standby motor that moves the kiln during power outages during an earthquake. The purpose of the indications of Figure A.11, detail 1, is the compatibility of seismic resistance with operating conditions. When calculating the seismic force H on support 3 it is admissible to discount the fric-tion of supports 1, 2 and 4 using a friction coefficient equal to 0.1.

C.11.9.2 Detail 2 of Figure A.11 summarizes the design provisions for the lateral seism. The

calculation of overturning has not the purpose of preventing this occurrence, which is no real possibility, but to avert rising and alternate impacts on both sides, known as “tapping”.

The failure of the longitudinal push rollers may cause important displacements (51). To prevent falling it is necessary that the width of the wheel rim be increased, as per Figure A.11, detail 2.

C.11.10 Refractory brickwork structures C.11.10.1 The high temperature resistance characteristics of refractory bricks are seldom known.

Mortar disappears or transforms itself with temperature and the resistance frequently depends from thermal compressions. Brickwork usually does not react elastically and

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it has no reliable tensile resistance. Therefore, brickwork shall not be considered as structural or earthquake-resistant element. Figure A.12 presents two foundry fur-naces, one with an arched roof that resists vertical and horizontal forces, and the other one with a non-structural roof suspended from a steel structure. The first ones failed but not the other ones during the Chilean seism (1, 27, 32)

Industrial brickwork requires continuous collaboration of process engineers and pro-fessional specialists from the very beginning of every project.

C.11.10.2 The static method usually serves the purpose in furnaces such as that of Figure A.12

b). However, more complex furnaces with suspended reactors or coolers, such as the flash furnaces of the copper industry, require dynamic spectral analyses.

C.11.10.3 The structure prior to its heating is in a condition that is different than its normal con-

dition, as provision has been made for expansion gaps as shown on Figure A.12 b) . This condition may last in most cases for hours or days but it is not necessary to con-sider it coincident with the design seism.

C.11.11 Electric equipment C.11.11.1 Electric equipment is essential for any industry, because of the energy and communi-

cations necessities after a seism. There are special seismic design specifications or in-ternational standards of accepted and proven application, which are out of the scope of this standard. The best-known ones in Chile are those issued by Empresa Nacional de Electricidad – ENDESA General Technical Specifications 1.015, prepared by Prof. Arturo Arias (52).

C.11.11.2 The ENDESA standard defines robust equipment as equipment whose function de-

termines that the design considers stresses that by far exceed seismic stresses, that they have no fragile components, and that equipments with fundamental frequencies of 30 Hz or more are considered as rigid equipments. Typical examples are genera-tors, engines, valves, pumps and similar facilities. The recommended formulas for static design are based on the ENDESA specifications (52).

C.11.11.3 The recommendations for isolators are taken from ENDESA specifications (52).

Equipment that does not meet the conditions of robustness and stiffness may require dynamic or empiric analyses. For dynamic analyses, the ENDESA specification pre-scribes equipment-dependent spectra, damping and R values in most cases; in the main, they are severer than this standard. Empiric qualification tests consist of oscil-lation assessments for determining frequencies and damping, tests under static forces, on vibratory tables or similar elements. These specifications are mandatory for impor-tant equipment, such as encapsulated substations.

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C.11.12 Minor structures and equipment

Industries have many minor elements, such as pumps, engines, compact boilers, boards, racks and similar elements, most of which have good structural resistance. However their anchorages, connections and other details may fail and some times cause protracted standstills. It is essential that all these details be seismically verified and that the required reinforcements be implemented; most of them are simple and may be installed in-site. Figure A.13 illustrates such cases.

C.11.13 Wood structures

The provisions are based on NCh1198 supplemented by SEAOC and UBC recom-mendations (4 and 5) as well as on the New Zealand standards referenced in North American publications. Structural failure can be due to the wood, to flexure or tension or in the connections. The failure in wood is fragile and in connections it can be ductile. Structures in general are classified into ductile, non-ductile or semi-ductile. Ductile structures have ductile connections that are less resistant than the wood. Typi-cal ductile structures are those that resist seismic forces with braced walls or dia-phragms connected by bolts or nails, structures with wood-to-wood connections of small diameter bolts or nails, or structures with toothed plate or steel plate connec-tions. Non-ductile structures have connections of greater resistance than the wood that fails on account of tension or flexure. Most structures have stiff glued connections or connections with over 20 mm diameter bolts. Semi-ductile structures are an intermediate structure of the abovementioned. The recommended R values are: 4 for ductile structures; 1 for non-ductile structures, and 2.5 for semi-ductile structures.

C.B Design of beam-column connections in stiff steel frames C.B.1 General

The AISC Standard (10 and 11) includes provisions for the design of the panel zone, which is the beam web that faces the moment connections of the beam, zone that is designed to resist the frequently important generated shear. AISC prescribes special conditions for the seismic case of stiff frames (20) with the purpose of preventing failures due to lack of ductility, as were observed at the Loma Prieta and Northridge earthquakes, and often require testing.

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No such failures have been observed in Chile, because the maximum seismic defor-mations of our standards are approximately half of the North American values. Therefore, this standard omits AISC special provisions, except for a few minor excep-tions.

C.B.2 Design of the panel zone of moment connections

This includes the design provisions in detail. When the web thickness is insufficient, it shall be reinforced in the workshop with attached plates or welded diagonal stiffen-ers. Changing the column profile by another one with greater web thickness can obvi-ate these reinforcements. This is a matter of economy that ought to be reviewed in each case. The following table presents cost data published by AISC (54) with calcu-lated equivalents for Chile.

Costs expressed in kg of structural steel

U.S.A. Chile One attached plate 160 70 Two welded stiffeners with rivets 140 60 Two butt-welded stiffeners 450 200

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References

[1] Seismic Design of Industrial Structures in Chile, E. Arze, Third Canadian Conference on Earthquake Engineering, Montreal, June 1979.

[2] Estructuras e Instalaciones Industriales, E. Arze L. Seminario sobre la Norma Sísmica

Chilena NCh433, Instituto Nacional de Normalización, INN, Santiago Noviembre 1989.

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[5] Recommended Lateral Force Requirements and Tentative Commentary, Seismology Committee of the Structural Engineers Association of California, SEAOC, 1997, San Francisco, California.

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Azócar, Depto. De Ingeniería de Construcción, Publicación 112, Pontificia Universidad Católica de Chile, Santiago 1988.

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[14] A Structural Dynamic Analysis of Steel Plant Structures subjected to the May 1960 Chilean Earthquakes, J.A. Blume, Bulletin Seismological Society of America, Febru-ary, 1963.

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World Conference on Earthquake Engineering, Tokyo 1960.

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[29] The Chilean Earthquake of May 1960, A Structural Engineering View Point, K.V. Steinbrugge, R. Flores, Bulletin of the Seismological Society of America, February 1963.

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quake Engineering Research Institute, Oakland, California 1994.

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Association AWWA D100, D110 y D115, 1996.

[42] Concrete Tanks for water Storage, ACI 350-3, 1999.

[43] Seismic Design of Storage Tanks, New Zealand National Society for Earthquake Engi-neering, 1996.

[44] General Structural Design and Design Loadings for Buildings, New Zealand Standard

NZS 4203, 1992.

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[45] Non Building Structures Seismic Design Code Developments, H.O. Sprague and N.A. Legatos, Earthquakes Spectra, February 2000.

[46] The Prince of Williams Sound Alaska Earthquake of 1964, Oil Storage Tanks, J.E.

Rinne, U.S. Department of Commerce, Washington, DC 1967.

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[48] The Seismic Design of Industrial Plants, R.D. Evison et al, The Institution Of Profes-

sional Engineers, New Zealand 1982.

[49] Loma Prieta Earthquake Reconnaissance Report, Earthquake Spectra, California1990.

[50] Armenia Earthquake Reconnaissance Report, Earthquake Spectra, California 1989.

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[52] Especificaciones Técnicas Generales, ETG 1015 Diseño Sísmico, ENDESA 1987.

[53] Focus Wood Design, Buchanan, Dean and Deam, USA.

[54] Economy in Street Design, AISC Modern Steel Construction, 2000.