-
ENGINEERING STANDARD
EI - 004
WIND, EARTHQUAKE AND SNOW LOADING
Please discard any previous issue of this Standard.
Revision Number Log Rev. Date By Pages App. Remarks
0 1.07.96 PCA HPJ ISSUED FOR APPROVAL 1 16.08.96 PCA HPJ
APPROVED FOR DESIGN
2 7.01.97 PCA 1,5 HPJ REVISION TABLE 1, PAGE 5
3 30.01.97 PCA 3,4,5,8,11,12,13,16 HPJ REVISED PAGES 3, 4, 5, 8,
11, 12, 13 AND 16
4 9.05.97 PCA 3,6,7,8,14 HCS REVISED PAGES 3, 6, 7, 8, AND
14
5 7.7.97 PCA 6,8,14 HCS REVISED PAGES 6, 8 AND 14
6 20.8.97 PCA 3 HCS REVISED PAGE 3
7 15.9.97 PCA 3,8,13,19 HCS REVISED PAGES 3, 8, 13 AND 19
8 19.3.98 PCA 12 HCS REVISED PAGE 12
9 1.4.98 PCA 15 HCS REVISED PAGE 15
10 7.10.98 PCA All HCS GENERAL REVISION
11 7.5.01 S y S All HCS GENERAL REVISION
12 30.1.04 S y S 10 HLM REVISED PAGE 10
13 17.3.05 PCA ALL HLM GENERAL REVISION
14 26.4.05 S y S 1 TO 131 OF APPENDIX B HLM APPENDIX B
REPLACED
15 12.7.05 S y S 1, 35 TO 50 HLM REVISED PAGES 1, 35 TO 50
16 21.10.06 S y S i, ii, 1, 4 TO 6, 8 TO 11, 13 TO 17, 19 TO 27,
32, 34 TO
42 AND 49
HLM REVISED PAGES i, ii, 1, 4 TO 6, 8 TO 11, 13 TO 17, 19 TO 27,
32, 34 TO 42 AND 49
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 i
1.0 GENERAL REQUIREMENTS
........................................................................................1
1.1 Scope
....................................................................................................................................3
1.2 General
................................................................................................................................3
2.0
REFERENCES...................................................................................................................4
2.1 Enap Refineras Engineering
Standards..........................................................................4
2.2 U.S.A Specifications and Codes
........................................................................................4
2.3 Chilean Codes
.....................................................................................................................4
3.0 COMBINATIONS OF LOADS
........................................................................................5
3.1 General
................................................................................................................................5
3.2 Symbols and Notation
........................................................................................................5
3.3 Combining Nominal Loads using Allowable Stress
Design............................................6
3.3.1 Basic
Combinations....................................................................................................6
3.4 Combining Factored Loads Using Strength
Design........................................................7
3.4.1
Applicability................................................................................................................7
3.4.2 Basic
Combinations....................................................................................................7
4.0 WIND
LOADS....................................................................................................................8
4.1 General
................................................................................................................................8
4.1.1
Scope............................................................................................................................8
4.1.2 Allowed
Procedures....................................................................................................8
4.1.3 Minimum Design Wind Loading
..............................................................................8
4.1.3.1 Main Wind Force Resisting
System.....................................................................8
4.1.3.2 Components and Cladding
...................................................................................8
4.2 Basis of Loads
.....................................................................................................................9
4.3 Determination of wind forces
..........................................................................................10
4.3.1
Buildings....................................................................................................................10
4.3.2 Open type
structures................................................................................................11
4.3.3 Structures subjected to induced wind
vibration....................................................11
4.3.3.1 Vortex
Shedding.................................................................................................11
4.3.3.2 Prevention of Excessive
Vibration.....................................................................11
5.0 SEISMIC LOADS
............................................................................................................13
5.1 General Provisions
...........................................................................................................13
5.2 Seismic Design
Criteria....................................................................................................14
5.3 Allowable Deflection and
Drift........................................................................................16
5.4 Seismic Analysis Procedures
...........................................................................................18
5.4.1 General
......................................................................................................................18
5.4.1.1 Introduction
........................................................................................................18
5.4.1.2 Direction of the seismic
solicitation...................................................................19
5.4.1.3 Combination of effects of horizontal components of the
earthquake ................20 5.4.1.4 Mathematical
modeling......................................................................................20
5.4.2 Static Method of Analysis
........................................................................................22
5.4.3 Dynamic Method of Analysis
..................................................................................25
6.0 DESIGN SNOW LOADING
...........................................................................................33
7.0 GROUND-SUPPORTED FLAT-BOTTOM STEEL
TANKS.....................................34 7.1 Tanks
Classification
.........................................................................................................34
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 ii
7.2 Seismic Design
..................................................................................................................34
7.2.1
Scope..........................................................................................................................34
7.2.2 Generalities
...............................................................................................................34
7.2.3 Design Spectral Response Accelerations
................................................................34
7.2.4 Base
Shear.................................................................................................................35
7.2.5 Overturning
Moment...............................................................................................36
7.2.6 Anchorage Ratio for Self-anchored Tanks
............................................................37
7.2.7 Sliding
Resistance.....................................................................................................38
7.2.8 Anchorage
.................................................................................................................39
7.2.8.1 Anchor Bolts
......................................................................................................39
7.2.8.2 Anchor Chairs
....................................................................................................39
7.2.8.3 Shear Device
......................................................................................................40
7.2.9
Freeboard..................................................................................................................40
7.2.10 Construction
requirements......................................................................................41
8.0 SEISMIC DESIGN OF PRESSURE
VESSELS............................................................42
8.1 Scope
..................................................................................................................................42
8.2 General requirements
......................................................................................................42
8.2.1 Risk classification
.....................................................................................................42
8.2.2 Combination
loads....................................................................................................43
8.2.3 Seismic loads
.............................................................................................................43
8.2.4 Mathematical model of the pressure
vessel............................................................44
8.2.5 Seismic analysis
........................................................................................................45
8.3 Seismic design of vertical pressure vessels
.....................................................................46
8.4 Seismic design of horizontal cylindrical pressure vessels
.............................................46 8.5 Secondary
elements attached to pressure
vessel............................................................46
8.6 Seismic design of anchorage system
...............................................................................47
8.7 Other considerations
........................................................................................................50
Table 5.1 Importance
Factor....................................................................................................28
Table 5.2 Plan Structural Irregularities
.................................................................................29
Table 5.3 Vertical Structural Irregularities
...........................................................................30
Table 5.4 Allowable Story Drift
...............................................................................................30
Table 5.5 Response Modification Coefficients and Deformation
Coefficient......................31 Table 5.6 Horizontal Force
Factors.........................................................................................32
Table 5.7 Modal Design Damping
Ratios................................................................................32
Table 5.8 Hazard
Factor...........................................................................................................32
Table 7.1 Anchorage
Ratio.......................................................................................................38
Table 8.1 Risk Grade
................................................................................................................42
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 1
1.0 GENERAL REQUIREMENTS
This standard provides the minimum design basis for wind,
earthquake and snow loading to be imposed on building, structures,
vessels and equipments.
Chilean standards NCh 2369 Earthquake-resistant design of
industrial structures and
facilities and NCh 433 Earthquake resistant design of buildings
included in the appendices B and C form part of these
requirements.
The requirements indicated in this standard shall be applied as
a whole. The load combinations of Chapter 3.0 are consistent with
the loading conditions indicated in Chapters 4.0 to 8.0.
For wind loads, Chapter 4.0 replaces the Chilean standard NCh
432 Calculation of the
action of wind on structures. For seismic loads, Chapter 5.0
prevails over NCh 2369. However the special NCh 2369
requirements of chapters 8, 9, 10, and 11 for steel structures,
reinforced concrete structures, foundations and specific structures
respectively are not modified by this standard and have to be
fulfilled, except 11.7 and 11.8 for tanks where Chapters 7.0 and
8.0 of this standard prevail over NCh 2369.
The loading conditions indicated in Chapters 4.0 to 8.0, are
only applicable to the location of Enap Refineras plant at
Talcahuano.
Talcahuano is located near Concepcin, an earthquake prone zone,
characterized by large
subduction earthquakes of Richter magnitude Ms = 8.5 with
epicenters off-shore at approximately 40[km] from Talcahuano and a
focal depth of 40[km]. The seismic zone is 3 according to NCh.
2369.
The studies of seismic risk have already been done and their
recommendations are fully
included in these bases, according to NCh 2369 Section 5.8. Soil
classification at Enap Refineras plant is Soil Type III. All
structures, buildings, equipment and pieces of equipment shall have
sufficient strength
to withstand seismic actions in accordance with these
specifications. In accordance with section 4.6 of NCh 2369, design
of structures shall be done by
engineers authorized to practice in Chile, with at least five
years of proven experience in Seismic Design. Exception is made
with equipment designed by foreign suppliers.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 2
Seismic Design of all structures, equipment and their anchorages
shall be reviewed and approved by engineers responsible to Enap
Refineras, with 10 years or more of experience in Seismic Design,
authorized to practice in Chile as indicated in section 4.6 of NCh
2369.
Contractor shall submit for review their calculation sheets and
structural drawings, at own
expenses, to a local Seismic Reviewer previously approved by
Enap Refineras. It is the Contractors responsibility to ensure that
the seismic review considers not only
the building and/or equipment, but also the foundations in the
context of an integral system. Parameters and methods for seismic
analysis shall be established by Enap Refineras, or
approved by the Seismic Reviewers, upon proposals by structural
designers and equipment suppliers. An example of acceptable form
for submitting these parameters are shown in Appendix A.
Suppliers must submit the following information for
approval:
Structural diagrams, drawings and/or sketches, signed by the
designers, detailing the structures or structural components of
equipment under analysis.
Identification of material used. Detail of the load cases and
load combinations considered in the analysis. Details of the
structures mathematical models used, indicating sections,
releases,
orientation of members, etc. Identification of the computer
programs, and description of the same, if it is requested by
the reviewers. Verification of maximum seismic deformations and
drifts. Complete computation sheets, signed by the designers, for
all structures, structural
components of equipment, connections and anchorages. If computer
programs are used, complete input and result sheets.
Calculation report with a clear explanation of the analysis
performed, accompanying the former documents. Exception is made
with Class C3 minor structures and equipment, in which it is
sufficient
to submit drawings with dimensions, weights, centers of gravity,
material properties and anchoring devices, also signed by
designers.
The review and approval does not relieve the suppliers
responsibility for the supply
fulfillment of all structural and seismic specifications.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 3
1.1 Scope 1.1.1 These general design criteria shall apply to
equipment, piping, structures and buildings to
be designed by the Supplier for Enap Refineras plant at
Talcahuano. 1.1.2 All particular seismic design requirements are
included in Section 7.0 Ground-Supported
Flat-Bottom Steel Tank and Section 8.0 Seismic Design of
Pressure Vessels. 1.1.3 All structural requirements and loading
conditions that are not explicit in above
mentioned criteria shall be defined by the Supplier and
submitted to the Project Manager for approval.
It shall be mandatory for the Supplier to indicate anyone
deviation and not explicit requirement or condition in order to
obtain the approval from the Project Manager for all of them.
1.1.4 The approval by the Project Manager shall be granted
without detriment of correspondent
responsibility of the Supplier. 1.1.5 Design criteria prepared
by the Supplier cannot modify any requirement of this design
standard. If it happens, the modification or substitution will
be void and considered as non-existent.
1.1.6 Design and drawings that not fulfilling this design
standard must be redone, even if the
Project Manager had mistakenly approved them. 1.1.7 Any
complement, modification or substitution to this design standard
should be admitted
and agreed before the signature of the contract. 1.2 General
1.2.1 Drawing sizes, titles, notes and numbers shall conform to
Enap Refineras Engineering
Standard EI-006. 1.2.2 Drawings, documents and computations
prepared by foreign Engineers and/or
Manufactures working for the Supplier shall be prepared in
Spanish or English language. Work done in Chile shall be in Spanish
language.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 4
2.0 REFERENCES 2.1 Enap Refineras Engineering Standards 2.1.1
EI-001 Structural Steel Design and Fabrication. 2.1.2 EI-002
Foundations and Elevated Structures. 2.1.3 EI-003 Design Loading
for Equipment, Structures, Buildings and Foundations. 2.1.4 EI-005
Anchor Bolts. 2.1.5 EI-006 Dibujos en AutoCad. 2.1.6 EI-007
Underground Piping and Surface Drainage. 2.1.7 EI-010 Fabricacin,
Montaje y Controles de Estructuras de Acero. 2.2 U.S.A
Specifications and Codes 2.2.1 ASCE/SEI 7-05, Minimum Design Loads
for Buildings and Other Structures. 2.2.2 UBC 1997, Uniform
Building Code. 2.2.3 AISC, Manual of Steel Construction, Allowable
Stress Design, Ninth Edition, 1989. 2.2.4 AISC, Manual of Steel
Construction, Load and Resistance Factor Design. Volume I.
Structural Members, Specifications & Codes, Second Edition,
1998. 2.2.5 AISC, Seismic Provisions for Structural Steel
Buildings, April 1997. 2.2.6 AISC, Seismic Provisions for
Structural Steel Buildings. Supplement No. 2
November, 10, 2000. 2.2.7 ACI 318-99, Building Code Requirements
for Structural Concrete. 2.2.8 American Petroleum Institute (API):
Welded Steel Tanks for Oil Storage. API Standard
650. Tenth Edition, November 1998. Addendum 1, January 2000.
Addendum 2, November 2001. Addendum 3, September 2003. Addendum 4,
December 2005.
2.3 Chilean Codes 2.3.1 NCh 2369 Of. 2003, Earthquake-Resistant
Design of Industrial Structures and
Facilities. 2.3.2 NCh 433 Of. 1996, Earthquake Resistant Design
of Buildings.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 5
3.0 COMBINATIONS OF LOADS
This Section prevails over Section 4.5 of NCh 2369. 3.1
General
Loading combinations shall be according to the provisions of
Enap Refineras engineering standard indicated in 2.1.3 and in this
chapter. 3.2 Symbols and Notation
The following nominal loads shall be considered: D = Dead load
as defined in Enap Refineras Engineering Standard EI-003 paragraph
III.A; Eh = Horizontal earthquake load given in Chapter 5.0; Ev =
Vertical earthquake load given in Chapter 5.0; F = Load due to
fluids with well-defined pressures and maximum heights; H = Load
due to lateral earth pressure, ground water pressure, or pressure
of bulk materials; L = Live load as defined in Enap Refineras
Engineering Standard EI-003 paragraph III.B; La = Accidental live
loads, originated by events that occur only occasionally during the
normal
use of installations. They include: Extreme impacts and
explosions. Short-circuit loads. Loads due to over filling of tanks
and bins.
Lo = Operation live loads as defined in Enap Refineras
Engineering Standard EI-003 paragraph III.C;
Lr = Roof live load as defined in Enap Refineras Engineering
Standard EI-003 paragraph III.B;
T = Self-straining force (Provision shall be made for
anticipated self-straining forces arising from differential
settlements of foundations and from restrained dimensional changes
due to temperature, moisture, shrinkage, creep, and similar
effects). Thermal forces are defined in Enap Refineras Engineering
Standard EI-003 paragraph III.D;
W = Wind load given in Chapter 4.0; M = Erection loads; K1 =
Live load reduction coefficient defined in paragraph 5.2.13; K2 =
Damping correction coefficient; 1.1 for steel structures and
equipment and 1.4 for
concrete structures; IR = Hazard Factor from Table 5.8 for
piperacks. Equal 1.0 for all other cases.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 6
3.3 Combining Nominal Loads using Allowable Stress Design 3.3.1
Basic Combinations
Loads listed herein shall be considered to act in the following
combinations, whichever produces the most unfavorable effect in the
building, foundation, or structural member being considered.
Effects of one or more loads not acting shall be considered. D + Lo
(1) D + L + F + H + T + Lr + Lo + La (2) D + W + L + Lr + Lo (3) D
+ K1L +Lr + Lo + La + IR(Eh + Ev) (4) D + W + H (5) D + H + La +
IR(Eh + Ev) (6) D + M (7) Exception: Loads Lo and La are combined
with earthquake in combination (4) and (6) only if
the following conditions are met: La action is originated by the
earthquake; in such a case, it must be included
with its proper sign. It is normal that, at the beginning of the
earthquake, Lo is acting and it is not
stopped or interrupted because of it.
If the earthquake originates an effect by which Lo and La
actions are interrupted at the beginning of the seismic movements,
such actions might not be considered. Load combinations for Chapter
7.0 are indicated in Appendix R of API 650 standard.
The most unfavorable effects from both wind and earthquake loads
shall be considered,
where appropriate, but they need not be assumed to act
simultaneously.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 7
3.4 Combining Factored Loads Using Strength Design 3.4.1
Applicability
The load combinations and load factors given in Section 3.4.2
shall be used only in those cases in which they are specifically
authorized by the applicable material design standard. 3.4.2 Basic
Combinations
Structures, components, and foundations shall be designed so
that their design strength equals or exceeds the effects of the
factored loads in the following combinations: 1.4(D + F) (1) 1.2(D
+ F + T) + 1.6(L + H + Lo) + 0.5Lr (2) 1.2D + 1.6Lr + 0.5L + Lo (3)
1.2D + 1.6Lr + 0.8W (4) 1.2D + 1.6W + 0.5(L + Lo) + 0.5Lr (5) 1.2D
+ K1L + Lo + La + IRK2(Eh + Ev) (6) 0.9D + 1.6W + 1.6H (7) 0.9D +
1.6H + La + IR(K2Eh + 0.3Ev) (8) 1.4(D + F) + 1.6M (9) Exception:
The load factor on H shall be set equal to zero in combination (7)
and (8) if the
structural action due to H counteracts that due to W, Eh or Ev.
Where lateral earth pressure provides resistance to structural
actions from other forces, it shall not be included in H, but shall
be included in the design resistance.
Loads Lo and La are combined with earthquake in combination (6)
and (8) only if the conditions indicated in section 3.3.1 are
met
Each relevant strength limit state shall be investigated.
Effects of one or more loads not
acting shall be investigated. The most unfavorable effects from
both wind and earthquake loads shall be investigated, where
appropriate, but they need not be considered to act
simultaneously.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 8
4.0 WIND LOADS 4.1 General
This Chapter replaces the Chilean standard NCh 432. 4.1.1
Scope
Building and other structures, including the main wind force
resisting system and all components and cladding thereof, shall be
designed and constructed to resist wind loads as specified in
ASCE/SEI 7-05 and in this Engineering Standard. 4.1.2 Allowed
Procedures
The design wind loads for buildings and other structures,
including the main wind force resisting system, components and
cladding elements thereof, shall be determined using one of the
following procedures specified in the ASCE/SEI 7-05:
Method 1: Simplified Procedure as specified in ASCE/SEI 7-05
Section 6.4 for buildings or structures meeting the requirements
specified therein.
Method 2: Analytical Procedure as specified in ASCE/SEI 7-05
Section 6.5 for buildings or structures meeting the requirements
specified therein.
Method 3: Wind Tunnel Procedure as specified in ASCE/SEI 7-05
Section 6.6. 4.1.3 Minimum Design Wind Loading
The design wind load, determined by any one of the procedures
specified in Section 4.1.2, shall be not less than specified in
this section. 4.1.3.1 Main Wind Force Resisting System
The wind load to be used in the design of the main wind force
resisting system for an enclosed or partially enclosed building or
other structures shall not be less than 84[kgf/m2] (0.83[kN/m2])
multiplied by the area of the building or structures projected onto
a vertical plane normal to the assumed wind direction.
The design wind force for open buildings and other structures
shall be not less than 84[kgf/m2] (0.83[kN/m2]) multiplied by the
area Af. The area Af is defined in ASCE/SEI 7-05 Section 6.3.
4.1.3.2 Components and Cladding
The design wind pressure for components and cladding of
buildings shall be not less than a net pressure of 84[kgf/m2]
(0.83[kN/m2]) acting in either direction normal to the surface.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 9
4.2 Basis of Loads 4.2.1 Design wind loads shall be determined
by one of the procedures specified in Section
4.1.2. The following are the design parameters required to
calculate such forces: 4.2.1.1 The exposure category shall be C,
according to ASCE/SEI 7-05 Section 6.5.6.3. 4.2.1.2 All structures
shall be classified as Category IV (Table 1-1 of ASCE/SEI 7-05),
and
the importance factor shall be 1.15. 4.2.1.3 The basic wind
speed at 10[m] above ground level shall be 140[km/hr] (87[mph]).
4.2.1.4 Inside the Enap Refineras plant the topographic factor Kzt
shall be 1.0. 4.2.1.5 The following values can be used for the
critical damping ratio (). This is valid only
for the determination of the gust effect factor for flexible or
dynamically sensitive structures.
Structural System Steel frames with welded connections, with or
without bracings. Shell of steel welded; stacks, bin, tanks,
vessels, tower, piping, etc.
0.003
Steel frames with field-bolted connections, with or without
bracings. 0.005 Structures of reinforced concrete and masonry.
0.008
4.2.2 The gust effect factor Gf for rigid structures defined in
ASCE/SEI 7-05 Section 6.2 shall
be considered equal to 0.85. 4.2.3 For chimneys, stack, flare
stacks and other aerodynamically excitable structures the value
of Gf shall be calculated according to Section 6.5.8.2 of
ASCE/SEI 7-05. The minimum value for Gf shall be 0.85 (Flexible or
dynamically sensitive structures are defined in Section 6.2 of
ASCE/SEI 7-05).
4.2.4 No allowance for the direct shielding effects of other
structures or terrain features shall be
permitted in this standard, as stated in Section 6.5.2.1 of
ASCE/SEI 7-05. However, any increase in pressure or suction on
structures as a result of such obstructions shall be considered in
design.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 10
4.2.5 Generally, the structure shall be designed based on the
wind load applied along the two principal axes of the structure.
Other wind directions may require to be considered depending on the
shape of the structure, such as a tall polygonal structure.
4.2.6 All structures and foundations subjected to wind load
shall be designed to resist the
pressures and suctions over the vertical surfaces and roof,
including appurtenances. 4.2.7 Any direction shall be considered as
prevailing direction of wind if real ones are not
known. It will be supposed that wind works horizontally. 4.2.8
Maximum horizontal deflection for rigid structures defined in
ASCE/SEI 7-05 Section
6.2, in the static wind design will be less than 5[mm] each
meter of height, deflection/height = 1/200.
4.2.9 For vertical vessels, chimney, stacks, flare stacks, high
tower, the allowable deflection at
the top of vertical equipment shall not exceed H/150, where H is
the total equipment height; the calculation of the deflection shall
be carried out for equipment in corroded condition.
4.2.10 For flexible or dynamically sensitive structures defined
in ASCE/SEI 7-05 Section 6.2,
this figure has to be reduced to 2.5[mm] each meter height,
deflection/height = 1/400. 4.2.11 For chimney, high towers, stacks,
where ratio height/diameter or height/width were higher
than 10 it shall be necessary to carry out a vibration check for
the vortex shedding effect by a recognized procedure, or the
procedure indicated in Section 4.3.3.
4.2.12 For Section 4.2.11, a recognized procedure is the one
according to the Engineering
Sciences Data Unit (ESDU, London). By this method are checked
both the critical velocity of the wind (velocity exciting the
phenomenon) and the value of the fatigue stresses induced in any
section of the structure. The following values are to be assumed
for the logarithmic decrement:
Empty column (without internals): 0.030 Installed column (with
trays and structures): 0.033 Column during operation: 0.035
4.3 Determination of wind forces 4.3.1 Buildings
Wind load on enclosed buildings and their components and
cladding shall be calculated in accordance with Section 4.1.2.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 11
4.3.2 Open type structures
The design wind loading for open type structures shall be based
on the exposed area of the framing, including the supported
equipment and piping, which may be conservatively estimated as a
percentage of the gross projected area, and the forces
coefficients, Cf, for trussed tower as shown on Figure 6-23 of the
ASCE/SEI 7-05. 4.3.3 Structures subjected to induced wind
vibration
Structures such as stacks, above grade pipelines and other
excitable structures must have a fundamental period of vibration
different from, and preferably less than the period of the wind
pulsation force (vortex shedding forces). 4.3.3.1 Vortex
Shedding
The mean hourly design speed, in meters per second, at the
equivalent height of the structure is denoted by VD and is
determined from equation 6-14 of ASCE/SEI 7-05.
The critical wind speed, in meters per second, is given by:
STdVC =
Where:
=T The fundamental natural period of a stack, second; =d Mean
diameter of upper one-third of stack, meters; =S Strouhal number
usually used as 0.2 is for single stack and may vary due to
Reynolds
numbers and multiple stacks.
The fundamental period of the structure must be calculated by an
acceptable method.
If VC > 1.3VD, then no vortex shedding consideration is
required. For other cases see Section 4.3.3.2. 4.3.3.2 Prevention
of Excessive Vibration
Many methods have been used in the prevention of excessive
vibrations in stack designs. It is not the purpose of this standard
to determine the exact method to be used in the design of stacks,
but rather to indicate some methods that have been successfully
used.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 12
The resonant vibration of a steel stack can be prevented or
diminished by including in the design one or more features that are
described below under three general categories: aerodynamic
methods, damping methods, and stiffening methods.
Aerodynamic Methods:
These are methods that disrupt the formation of vortices on the
sides of the stack. They are preferred over other methods because,
unlike the others, they remove the source of vibration, i.e., the
periodic vortex shedding forces (for example: Helical Strakes or
Shrouds).
Damping Methods:
These methods consist of attachments and auxiliary structures
that absorb dynamic energy from the moving stack.
Stiffness Methods:
These methods can be applied to the design to modify the
vibration characteristic of the stack and thus reduce the
probability that resonant vibration will occur.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 13
5.0 SEISMIC LOADS 5.1 General Provisions 5.1.1 Industrial
structures, equipment and their supporting structures shall be
designed in
accordance with Chilean standard NCh 2369 Earthquake-Resistant
Design of Industrial Structures and Facilities, complemented or
modified by this Standard.
In the following paragraphs, the sections that modify the
standard NCh 2369 are explicitly identified; those sections without
explicit references to NCh 2369 are complementary to it. Office,
residential, assembly and similar buildings, may be designed in
accordance with Chilean standard NCh 433 Earthquake Resistant
Design of Buildings.
5.1.2 Seismic design considers serviceability requirements
besides safe earthquake behavior of
buildings, structures, vessels and equipments.
Serviceability requirements refer to the operation of the
buildings, structures, vessels and equipment after the earthquake
with minor interruptions. This condition means only partial levels
of ductility. By economic reasons a shutdown longer than one week
is not acceptable (Category C1 according to Table 5.1).
5.1.3 The term structure refers to open frame structures with or
without rigid floor
diaphragms at various level; e.g. equipment supporting
structure, steel structure, tower, tank, stack, piperack, piping
support, stair, ladder, etc.
5.1.4 The term building refers to enclosed structures with walls
and interior partitions
supported by rigid floor diaphragms at various levels. 5.1.5 The
term rigid component refers to component, including its
attachments, having a
fundamental period less than or equal to 0.06[s]. 5.1.6 The term
flexible component refers to component, including its attachments,
having a
fundamental period greater than 0.06[s]. 5.1.7 Structures
designed to resist earthquake forces should be able of absorbing
large
quantities of energy beyond the elastic range before ultimate
failure. Such structures should have a consistent stress level or
margin of reserve strength throughout. Attention must be given to
those structural elements being specially designed for ductility
and against sudden brittle or buckling type of failure. The
structures shall have enough ductility so as to justify the
response modification coefficient R, detailed hereinafter. To
comply with this, concrete structures must satisfy the requirement
of Chapter 21 of ACI
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 14
318-99, as detailed in Chapter 9 of NCh 2369, and the other
requirements set forth therein. Steel structures must satisfy the
requirements of Chapter 8 of NCh 2369, or the Seismic Provisions
for Structural Steel Buildings, 1999 of AISC.
With the same basic purpose of providing enough ductility and
reserve strength, special consideration must be given of meeting
the requirements referred to joints, anchorage, bracing, detailing
and structural features of NCh 2369, Chapters 8 to 11 and Annex A
and B.
5.1.8 An importance factor, I, shall be assigned to each
structure or equipment in accordance
with Table 5.1. 5.1.9 In an adequate seismic design, as it is
herein recommended, yielding occur in very
specific elements, designed under that scope. However for
elements and connections specifically reinforced, their yielding
should not produce important effects and deformations on structures
and equipments, since the economical criteria to minimize the
shutdown will prevail over safety criteria only.
5.1.10 The seismic forces resulting from a large earthquake are
in general larger than design
forces and frequently larger than the forces that produce
yielding. In this regard these seismic recommendations are stricter
than recommendations given by codes for seismic design of normal
use in which economical reasons are not explicitly included.
5.1.11 Therefore, the particular requirements of this
Engineering Standard shall prevail over all
here mentioned Codes or Standards. 5.2 Seismic Design Criteria
5.2.1 Steel and Concrete Buildings, and other structures and their
components shall be designed
to meet the seismic requirements set forth in the following
paragraphs.
5.2.2 The design seismic forces, and their distribution over the
height of the structure, shall be established in accordance with
the procedures indicated in Sections 5.4.2 and 5.4.3. The
corresponding internal forces in structural members shall be
determined using a linearly elastic model.
5.2.3 Individual members shall be provided with adequate
strength to resist the shear, axial
forces, and moments determined in accordance with these
provisions. 5.2.4 A continuous load path, or paths, with adequate
strength and stiffness shall be provided to
transfer all forces from the point of application to the final
point of resistance.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 15
5.2.5 The foundation shall be designed to resist the forces
developed and shall accommodate the movements imparted to the
structure by the design ground motions.
5.2.6 The structure shall be single in order to obtain a
structural behavior that is easy to understand and to model. All
the forces shall be transferred to the foundations in a direct
way.
5.2.7 The seismic analysis shall be made using the static or the
dynamic analysis. Generally a
static analysis will be sufficient, provided that buildings,
structures, vessels and equipment have their masses and stiffnesses
regularly distributed in plan and in height. Regular distribution
is to be assumed when a deviation of 20 percent of uniform
distribution is not exceeded.
5.2.8 Static analysis should be used in buildings, structures,
vessels and equipment susceptible
of being reduced to one-degree-of-freedom system. 5.2.9 Dynamic
analysis shall be used in buildings, structures, vessels and
equipment including
but not limited to the following: 5.2.9.1 Equipment with height
larger than 20[m]. 5.2.9.2 Buildings and structures irregular in
plan configuration: Structures having one or
more of the irregularity typed listed in Table 5.2. 5.2.9.3
Buildings and structures irregular in vertical configuration:
Structures having one or
more of the irregularity typed listed in Table 5.3. 5.2.9.4
Buildings and structures supporting heavy hanging equipment.
5.2.9.5 Concrete or masonry lined stacks or tall vessels of a
height to horizontal dimension
ratio of five or more. 5.2.9.6 When specifically indicated by
Enap Refineras, for each project, in which the basic
assumptions of the static method do not apply. 5.2.10 When a
building or structure has been analyzed both by the static and the
dynamic
method, the latter shall prevail. 5.2.11 Whichever method of
seismic analysis is chosen, live load upon buildings,
structures,
vessels and equipment, are to be reduced in accordance with
their probability of occurrence under seismic condition.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 16
The following coefficients shall be applied in order to
determine the seismic live loads acting upon buildings, structures,
vessels and equipment: Locations K1 Storage warehouses, file rooms:
1.00 Fuel, water, or any material usually stored: 1.00 Operating
floors and others: 0.50 Maintenance areas Access, platforms and
walkways: 0.25 Roofs: 0.00
5.2.12 Components mounted on vibration isolation systems shall
have a bumper restraint or
snubber in each horizontal direction, and vertical restraints
shall be provided, constructed of ductile materials. A viscoelastic
pad or similar material of appropriate thickness shall be used
between the bumper and equipment item to limit the impact load.
5.3 Allowable Deflection and Drift 5.3.1 For the design of
structures the maximum allowable deflection for structural
elements
shall be as defined in this Section:
Structural Element Allowable Deflection (of span)
Beams in general due to dead loads plus live loads: 1/300 Beams
in pipe racks due to dead loads plus live loads: 1/150 Trusses due
to dead loads plus live loads: 1/700 Crane girders, vertical, due
to dead loads plus live loads and impact:
1/1000
Crane girders, horizontal due to impact: 1/500 Purlins, roof
sheets and wind columns due to dead loads and live loads:
1/200
Siding and girt due to wind loads: 1/200 Floor systems
supporting large open areas free of partitions or other sources of
damping, where vibration due to pedestrian traffic might be
objectionable, shall be designed with due regard for such
vibration. Mechanical equipment that can produce objectionable
vibrations in any portion of an inhabited structure shall be
isolated to minimize the transmission of such vibrations to the
structure.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 17
5.3.2 Seismic Deformations
This Section modifies Chapter 6 of NCh 2369 5.3.2.1 Horizontal
seismic deformations of the structural system must be compatible
with the
flexibility and strength of piping, ducts, walls, partitions and
other non-structural elements attached to the structure as well as
with the capacity of deformation of the ducts expansion joints.
However, shall not exceed the allowable story drift as obtained
from Section 5.3.2.2 at any story.
5.3.2.2 The design story drift () shall be computed as the
difference of the deflections at the
top and bottom of the story under consideration. For structures
having plan irregularity, the design story drift, , shall be
computed as the largest difference of the deflections along any of
the edges of the structure at the top and bottom of the story under
consideration.
The deflections of level x at any point, x, shall be determined
in accordance with the following equation:
IC xed
x=
Where:
=dC Deflection amplification factor from Table 5.5; =xe
Deflections determined by an elastic analysis;
=I Importance factor from Table 5.1. The elastic analysis of the
seismic force-resisting system shall be made using the prescribed
seismic design forces in Section 5.4.2 or 5.4.3. For the purpose of
this drift analysis only, the limitation of the minimum seismic
base shear specified in Section 5.4.2.3 or 5.4.3.9 is not
applicable for computing displacements. For determining compliance
with the story drift limitation of Table 5.4, the deflections of
level x at any point (x) shall be calculated as required in this
section. Flexible diaphragms, that is when the maximum lateral
deformation of the diaphragm is more than two times the average
story drift of the associated story, shall not be accepted. In case
that situation happens, enough horizontal bracings shall be added
to fulfill this requirement.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 18
5.3.2.3 Separation between adjacent buildings must be compatible
with seismic deformations according to Section 5.3.2.4.
5.3.2.4 Sufficient distance shall separate adjacent buildings or
structures to avoid contact,
when deflected by seismic action or seismic forces.
Separation shall be no less than the larger of the following
dimensions:
( ) ( )2xjdj2xidi CCS += h004.0S =
[ ]mm30S = Where:
xi and =xj Computed horizontal seismic deflection of each
structure determined in accordance with the procedure indicated in
Section 5.3.2.2;
diC and =djC Deflection amplification factor of each structure
from Table 5.5; =h Height of the structure at the considered
level.
5.3.2.5 An approach to the real seismic deflections of the
structure may be obtained from the
horizontal deflections gotten through a mathematical model
representative of the structure, when subjected to a response
spectrum modal analysis, using the spectrum of acceleration defined
in Section 5.4.3.9, multiplied by the factor Cd defined in Table
5.5.
5.4 Seismic Analysis Procedures 5.4.1 General 5.4.1.1
Introduction
This section defines two basic analytical procedures for the
seismic design. Both of them are based in the allowable stress
design method.
Static Method of Analysis. The Section 5.4.2 of this standard
modifies Section 5.3 of NCh 2369.
Dynamic Method of Analysis. The Section 5.4.3 of this standard
modifies Section 5.4 of NCh 2369.
The strength design method is permitted with the use of load
combination defined in Section 3.4.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 19
Limitations on the use of static method of analysis are
indicated in Sections 5.2.7, 5.2.8 and 5.2.9. The response
modification coefficient, R, and the deformation coefficient, Cd,
for mixed structural systems for the direction under analysis
(including the equipment) shall not exceed the lowest value
indicated in the Table 5.5. The modal design damping ratio, , for
mixed structural system (including the equipment) shall not exceed
the lowest value indicated in the Table 5.7. If an equipment or
component is supported above the base by another structure and the
weight of the equipment is not more than 25 percent of the seismic
weight, P, as defined in section 5.4.2.1, the design seismic forces
for the supported equipment shall be determined in accordance with
the requirement of section 5.4.2.4. If the weight of supported
equipment is more than 25 percent of the seismic weight, P, as
defined in section 5.4.2.1, the design seismic forces shall be
determined based on an analysis of the combined system (comprising
the equipment and supporting structure). For supported equipments
that have rigid component dynamic characteristics, the R response
modification coefficient for the supporting structural system shall
be used for the combined system. For supported equipments that have
flexible component dynamic characteristics, the R response
modification coefficient for the combined system shall not be
greater than 3. The equipment, and its supports and attachments,
shall be designed for the forces determined from the analysis of
the combined system.
5.4.1.2 Direction of the seismic solicitation The design ground
motion can occur along any direction of a structure. The analyses
shall be performed, as a minimum, for each one of two orthogonal or
approximately orthogonal horizontal directions. The effect of the
vertical seismic accelerations should be considered in the
following cases:
a. Suspension rods of hanging equipment and their supporting
beams. b. Structures and elements of prestressed concrete
(pretensioned and post-
tensioned). c. Foundations, anchorage elements and supports of
structures and equipment. d. Any structure or element in which the
vertical seismic action affects its
design, for example, long span or cantilever structures, shell
and shell-like structures, long span vaults or any structures with
unusual geometry or mass distribution.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 20
5.4.1.3 Combination of effects of horizontal components of the
earthquake
For the design of the structural earthquake resistant elements,
in general, it is not necessary to combine the effects of the two
horizontal components of the seismic action. The analyses shall be
performed for each one of the two horizontal directions considered
separately and independently. Make exception to this rule piperacks
and structures that present notorious torsional irregularities or
have special or intermediate moment frame in both directions. In
such cases, the elements should be designed for 100 percent of the
prescribed horizontal forces in one direction, plus 30 percent of
the prescribed forces in the perpendicular direction, and the same
shall be done in the perpendicular direction. The combination
requiring the greater element strength shall be used for the
design.
5.4.1.4 Mathematical modeling
(a) Basic assumptions In general, a building or structure should
be modeled, analyzed, and verified as a three-dimensional assembly
of elements and components. Two-dimensional modeling, analysis, and
verification of buildings or structures with stiff or rigid
diaphragms are acceptable if torsional effects are either
sufficiently small to be ignored or indirectly captured. For
irregular structures or structures without independent orthogonal
system, a three-dimensional model incorporating a minimum of three
degrees of freedom consisting of translation in two orthogonal plan
directions and torsional rotation about the vertical axis shall be
included at each level of the structure. Where the diaphragms are
not rigid compared with the vertical elements of the
lateral-force-resisting system, the model should include
representation of the diaphragms flexibility and additional dynamic
degrees of freedom, as required to account for the participation of
the diaphragm in the dynamic response of the structure. In the case
of structures having flexible diaphragms, special modeling and
computing considerations must be employed. In such case, it shall
be verified that the diaphragm fulfills the requirements indicated
in the Section 5.3.2.2. The equipment shall be included in the
model according to the recommendations of Section 5.4.1.1.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 21
(b) Horizontal eccentricity The effect of horizontal
eccentricity must be considered for building or structures with
diaphragms capable of resisting the forces generated by torsion.
The total torsional eccentricity at a given floor level shall be
set equal to the sum of the following two torsional
eccentricities:
The natural eccentricity; that is, the eccentricity between the
center of mass of all floors above and including the given floor,
and the center of rigidity of the vertical seismic elements in the
story below the given floor. This requirement is automatically
fulfilled in a three-dimensional model.
The accidental eccentricity; that is, an accidental eccentricity
produced by horizontal offset of the center of mass of all floors
above and including the given floor, obtained by the following
procedures: For both methods (static and dynamic):
HZb1.0e kky = For the seism applied in the X direction.
HZb1.0e kkx = For the seism applied in the Y direction.
Where: =e Design accidental eccentricity; =kxb Dimension in the
x direction of the k floor level; =kyb Dimension in the y direction
of the k floor level; =kZ Height of floor level k, over the base
level; =H Total height of the structure over the base level.
For dynamic method of analysis: A minimum of 5 percent of the
horizontal dimension at the given floor level measured
perpendicular to the direction of the applied load. The accidental
eccentricity must be simulated displacing the center of masses
horizontally in 5 percent in the mathematical model. On applying
these relations, the same sign must be considered on each level. In
general, two cases are necessary to be considered for each
directions of analysis.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 22
5.4.2 Static Method of Analysis
This Section modifies Section 5.3 of NCh 2369
5.4.2.1 The total shear load or base shear shall be computed in
the direction of each main axis of buildings, structures, vessels
and equipment with the following formula:
PI)T(CV =
Where:
=V Seismic base shear; ( )=TC Seismic coefficient modified by
the structure response, i.e., depending on the
fundamental period; =T Fundamental period (Natural period with
greater equivalent translational mass
in the direction of analysis); =I Importance factor from Table
5.1;
LKLDP 1o ++= Seismic weight; =1K Live reduction factor for
building, structures, vessels and equipment, defined
in Section 5.2.11; =D Vertical dead load (as per Engineering
Standard EI-003); =oL Vertical other loads when applicable (as per
Engineering Standard EI-003);
=L Unreduced vertical live load (as per Engineering Standard
EI-003). 5.4.2.2 Seismic coefficient modified by the structural
response: [ ] [ ]
( ) [ ] [ ][ ] [ ][ ] [ ]
[ ]
>
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 23
= Modal design damping ratio from Table 5.7. 5.4.2.3 The minimum
value for the seismic base shear (V) shall be:
PI12.002.0PR
I45.0V4.0
min
= Or the value established in NCh 2369 paragraph 5.8.1.3,
whichever be greater.
5.4.2.4 Horizontal force on elements of structures,
non-structural components and minor
equipment supported by structures, shall be calculated according
to the following formula (This article modifies Chapter 7 of NCh
2369):
ppp WCF =
Alternatively, Fp may be calculated using the following
formula:
pr
x*pp Wh
h31CF
+=
Except that: Fp shall not be less than pW5.0 Fp need not be more
than pW0.2 Where:
=pC Horizontal force factors from Table 5.6; =pW Weight of an
element or component; =*pC Horizontal force factor from Table 5.6;
=xh Height of element or component attachment level over to the
base level. Shall
not be taken less than 0; =rh Total height of the structure over
the base level.
5.4.2.5 For the cases indicated in sections 5.4.1.2.a and
5.4.1.2.b a vertical seismic
coefficient equal to 0.50 shall be considered to compute the
vertical seismic force acting simultaneously with horizontal
forces. For the cases indicated in sections 5.4.1.2.c and 5.4.1.2.d
a vertical seismic coefficient equal to 0.33 shall be considered to
compute the vertical seismic force acting simultaneously with
horizontal forces.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 24
5.4.2.6 If earthquake forces due to seismic torsion at any level
on any element exceed 50% of the earthquake forces without
eccentricity, the structure shall be analyzed by the dynamic method
or shall be modified to avoid this condition.
5.4.2.7 Vertical distribution of seismic forces. The lateral
seismic force (Fx) induced at any
level shall be determined from the following formula:
VWh
WhF n
1kkk
xxx
=
=
Where:
=V Total base shear load at the base of the structure; =xF
Lateral seismic force at Level x;
xW and =kW Portion of the total gravity load of the structure
(W) located or assigned to Level x or k;
xh and =kh Height from the base to Level x or k; =n Number of
level; = Exponent related to the structure period as follows: for
structures
having a period of 0.5[s] or less, = 1; for structures having a
period of 2.5[s] or more, = 2; and for structures having a period
between 0.5[s] and 2.5[s], shall be 2 or shall be determined by
linear interpolation between 1 and 2: = 1 + (T-0.5)/2
5.4.2.8 When stack, stack-like, cylindrical tanks and vessels
are allowed to be designed by
static analysis, seismic overturning moments shall be calculated
as follow: 5.4.2.8.1 In structures with a ratio of height/diameter
less than five, the moment diagram
will be calculated from shear forces as obtained in 5.4.2.7.
5.4.2.8.2 In structures with a ratio height/diameter bigger or
equal five, the moment diagram
will be obtained from dynamic method of analysis.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 25
5.4.3 Dynamic Method of Analysis
This Section modifies Section 5.4 of NCh 2369 5.4.3.1 A standard
calculation procedure based on two or three-dimensional model will
be
applied. The finite elements models used for dynamic analysis
should include a sufficient number of dynamic degrees of freedom
permitting selection of the most significant modes of vibration of
the structure.
5.4.3.2 According to Section 5.2.9 a dynamic seismic analysis
shall be carried out as required
in this document. As an additional option, Enap Refineras shall
require this analysis when considered necessary due to the
importance or characteristic of the structure. Method to be used
shall be response spectrum.
5.4.3.3 For doubly symmetric structures, vibrations must be
considered uncoupled in both
horizontal directions. Only accidental torsion shall be included
in the calculations, evaluating it statically.
5.4.3.4 For structures with only one axis of symmetry, vibration
modes in the direction of
this axis can be considered as uncoupled. 5.4.3.5 In general, a
three dimensional analysis shall be performed through a
computer
program, considering a minimum of three degrees of freedom at
each mass level: two horizontal displacements and a rotation around
a vertical axis through the center of gravity. In the case of
structures having flexible diaphragms special modeling and
computing considerations must be employed.
5.4.3.6 Modal shapes and frequencies have to be analyzed. If
they are found to be coupled,
without a clear or predominant direction of vibration for each
one of them, then a three-dimensional analysis with two directional
acceleration input as indicated in section 5.4.1.3, shall be
performed instead of two independent analyses.
5.4.3.7 The effect of the vertical seismic component for the
cases indicated in sections
5.4.1.2.a, 5.4.1.2.b, 5.4.1.2.c and 5.4.1.2.d shall be
considered. Analyses shall be carried out considering horizontal
and vertical seismic excitation acting simultaneously. For the
vertical component analysis, the design response spectrum defined
in section 5.4.3.9 with R=3 and =0.03 shall be used.
5.4.3.8 In special cases, like continuous structures, discrete
analysis can be used by dividing
them in segments, but not limited to that case, rotatory
inertias around horizontal axis may be important if discrete masses
are located quite far from the axis.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 26
A convenient number of degrees of freedom in connection with
rotational inertias have to be added in dynamic analysis for those
special cases.
5.4.3.9 Design response spectrum: [ ] [ ]
( ) [ ] [ ][ ] [ ][ ] [ ]
[ ]
>
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 27
5.4.3.12 The analysis shall include a sufficient number of modes
to obtain a combined modal mass participation of at least 90% of
the actual mass, but never less than the five first modes.
5.4.3.13 The modal damping considered in CQC criterion for the
computation of cross
correlation coefficient will be assumed equal for all modes and
with the value indicated in paragraph 5.4.1.1.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 28
Table 5.1 Importance Factor Category I
C1 Structure or vital equipments for the normal operation of the
plant. This category will be used by default except in those cases
in that Enap Refineras indicates the opposite. Maximum risk grade
pressure vessels. Medium risk grade pressure vessels that store
products with moderate or high fire or explosion hazard or products
biologically or environmentally dangerous.
1.00
C2 Structure or equipment that can have smaller damages than
quick repair and which do not cause important stoppage of the plant
or damages to structures of the previous category. Medium risk
grade pressure vessels that store products with low fire or
explosion hazard. Minimum risk grade pressure vessels that store
products with high fire or explosion hazard or products
biologically or environmentally dangerous.
0.80
C3 Provisional structure whose seismic fails it does not
endanger structures of the previous categories. Minimum risk grade
pressure vessels that store products biologically or
environmentally benign or products with low fire or explosion
hazard.
0.67
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 29
Table 5.2 Plan Structural Irregularities Item Irregularity Type
and Description
1 Non-approximately double symmetrical geometric configuration.
2 Potential large torsional moments due to significant eccentricity
between the seismic
resistant system and the tributary mass at any level. 3
Torsional irregularity to be considered when diaphragms are not
flexible. Torsional
irregularity shall be considered to exist when the maximum story
drift computed, including accidental torsion at one end of the
structure, transverse to an axis is bigger than 1.2 times the
average of the story drifts of the two ends of the structure along
the axis being considered.
4 Reentrants corners: Plan configurations of a structure and its
lateral force resisting system contain reentrants corners, where
both projections of the structure beyond a reentrants corner are
greater than 15 percent of the plan dimension of the structure in
the given direction.
5 Diaphragm discontinuity: Diaphragms with abrupt
discontinuities or variations in stiffness, including those having
cutout or open areas greater than 50 percent of the gross enclosed
diaphragm area, or changes in effective diaphragm stiffness of more
than 50 percent from one story to the next.
6 Out of plane offsets: Discontinuities in a lateral force path,
such as out of plane offset of the vertical elements.
7 Nonparallel systems: The vertical lateral force-resisting
elements are not parallel to or symmetric about the major
orthogonal axes of the lateral force resisting system.
8 Heavy-duty equipment, which is not uniformly distributed at
each floor level. 9 Theoretical centers of mass at each level,
which are non-approximately found in the
same vertical axes.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 30
Table 5.3 Vertical Structural Irregularities Item Irregularity
Type and Description
1 Mass-stiffness ratio between different stories or load levels
that varies significantly. 2 Weight (mass) irregularity. Mass
irregularity shall be considered to exist where the
effective mass of any story is more than 150 percent of the
effective mass of an adjacent story. A roof that is lighter than
the floor below need not be considered.
3 Stiffness irregularity or soft story. A soft story is one in
which the lateral stiffness is less than 70 percent of that in the
story above or less than 80 percent of the average stiffness of the
three stories above.
4 Important and obvious differences in stiffness of different
resistance lines. 5 Non-approximately symmetrical geometric
configuration about the vertical axes or
horizontal offset with significant dimensions. 6 Vertical
geometric irregularity. It shall be considered to exist where the
horizontal
dimension of the lateral force resisting system in any story is
more than 130 percent of that in an adjacent story.
7 In-plane discontinuity in vertical lateral-force-resisting
element shall be considered to exist where an in-plane offset of
the lateral force-resisting elements is greater than the length of
those elements or there exists a reduction in stiffness of the
resisting elements in the story below.
8 Discontinuity in lateral strength or weak story. A weak story
is one in which the story lateral strength is less than 80 percent
of that in the story above. The story strength is the total
strength of all seismic-resisting elements sharing the story shear
for the direction under consideration.
Table 5.4 Allowable Story Drift
Structure Masonry walls and partitions rigidly attached to
structure 0.0030hsx All other structures 0.0075hsx hsx is the story
height measured from ground to level x.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 31
Table 5.5 Response Modification Coefficients and Deformation
Coefficient Coefficient Type of Structural System
R Cd Reinforced Concrete Shear Walls 5.0 4.5 Reinforced Concrete
Ductile Moment Resisting Frames 5.0 4.5 Masonry Walls (Concrete
Blocks or Clay Bricks) 3.5 3.0 Intermediate Steel Moment Frames 5.0
4.0 Ordinary Steel Concentrically Braced Frames 5.0 4.0 Steel
Storage Racks 4.0 3.5 Elevated Tanks, Vessels, Bins or Hoppers: On
braced legs On unbraced legs Irregular braced legs single pedestal
or skirt supported Welded steel Concrete
3.0 3.0 2.0 2.0 2.0
2.5 2.5 2.0 2.0 2.0
Horizontal, saddle supported welded steel vessels 2.5 2.5 Tanks
or vessels supported on structural towers similar to building 3.0
2.0 Flat bottom, ground supported tanks, or vessels 3.0 2.5
Reinforced or prestressed concrete: Tanks with reinforced
nonsliding base Tanks with anchored flexible base
2.0 3.0
2.0 2.0
Cast-in-place concrete silos, stacks and chimneys having walls
continuous to the foundation
3.0
3.0
Steel Tanks, Elevated Tanks, Chimneys and Towers 2.5 2.5 Cooling
towers (Concrete, steel or wood frame) 3.5 3.0 Inverted
pendulum-type structures (not elevated tank) 2.0 2.0 Heavy
Equipment at Ground Level such as Power Transformers, Pumps,
Compressors, etc.
2.5 3.0
Hydrocracker Reactors 3.0 3.5 Hydrocracker Towers 2.5 3.0
Cylindrical Heaters 3.0 3.5 Towers Founded on Fixed Base at Ground
Level 2.5 3.0 Reactor Founded on Fixed Base at Ground Level 3.0 3.5
Heater Non-cylindrical Type 4.0 3.5 Pipe Rack Supported on Steel
Structure 5.0 4.0 Pipe Rack Supported on Reinforced Concrete
Structure 4.5 4.0 Other self-supporting structures, tanks or
vessels not covered above 1.25 2.5 Large Diameter Pipes 3.5 4.0
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 32
Table 5.6 Horizontal Force Factors Element *
pC Cp
Seismic restraint and guides of all equipment 0.250 1.0
Non-structural components, exterior and interior ornamentations and
appendages.
0.425 1.7
Walls and partitions, perpendicular to own plane 0.125 0.5
Cantilever walls and parapets 0.425 1.7 Connections of
prefabricated wall panels 0.500 2.0 Other components: Rigid
components Flexible components
0.350 0.500
1.4 2.0
Minor tanks and vessels (includes contents), including support
system 0.250 1.0 Any flexible equipment laterally braced or
anchored to the structural frame at a point below their center of
mass
0.425 1.7
Anchorage of expansion anchor bolts, chemical anchor bolts,
cast-in-place anchors bolts, anchorage constructed of non-ductile
materials or by use of adhesive
0.500 2.0
Table 5.7 Modal Design Damping Ratios
Structural System Steel frames with welded connections, with or
without bracings. Shell of steel welded, stacks, bin, tanks,
vessels, tower, piping, etc.
0.02
Steel frames with field-bolted connections, with or without
bracings. 0.03 Structures of reinforced concrete and masonry.
0.05
Table 5.8 Hazard Factor
Category Contents IR A Content is biologically or
environmentally benign, low fire or
low explosion hazard. 1.0
B Content is moderate fire or explosion hazard 1.1 C Content is
biologically or environmentally dangerous, high fire
hazard or high explosion hazard 1.2
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 33
6.0 DESIGN SNOW LOADING
No snow loading shall be considered for the design of the
structures and building.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 34
7.0 GROUND-SUPPORTED FLAT-BOTTOM STEEL TANKS
This Section prevails over Section 11.8 of NCh 2369. 7.1 Tanks
Classification
In accordance with the characteristic of stored liquid a
category from Table 5.8 shall be assigned to each tank. The
categories are associated with a hazard factor relative to the risk
of the content.
7.2 Seismic Design 7.2.1 Scope
This section provides minimum requirements for the seismic
design of welded ground-supported cylindrical liquid storage steel
tanks without internal pressure.
7.2.2 Generalities
The design and construction of storage steel tanks shall conform
to the requirements of the standard indicated in 2.2.8. The seismic
design shall be done as established in the Appendix E of API 650
standard except as indicated in sections 7.2.3 to 7.2.10. Some of
these exceptions are corrections to misprint API 650 equations.
7.2.3 Design Spectral Response Accelerations
The design response spectrum for ground supported flat bottom
steel tanks is defined by the following parameters:
Ri I36.0A = Self-anchored Tank; Ri I32.0A =
Mechanically-anchored Tank;
R40.1c
Rc I04.0T
I94.0A =
iv A32A =
Where:
=iA Impulsive design response spectrum acceleration coefficient,
%g (Damping ratio equal to 2 percent);
=cA Convective design response spectrum acceleration
coefficient, %g (Damping ratio equal to 0.5 percent);
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 35
=vA Vertical earthquake acceleration coefficient, %g; =RI Hazard
factor from Table 5.8; =cT Natural period of the convective
(sloshing) mode of behavior of the liquid,
seconds;
D
DH68.3tanh
578.08.1Tc
=
=D Nominal tank diameter, m; =H Maximum design product level,
m;
EDt
HCT
u
ii
=
=iT Natural period of vibration for impulsive mode, seconds. The
design methods in this standard are independent of impulsive period
of the tank. Expression for
iT given in this standard is applicable only to those circular
tanks in which wall is rigidly attached to base slab;
+
=2i
DH067.0
DH3.046.0
DH
1C
=ut Equivalent uniform thickness of tank shell, m; = Mass
density of fluid, kg/m3; =E Elastic Modulus of tank material,
N/m2,
7.2.4 Base Shear
The base shear due to seismic forces applied to the bottom of
the tank floor shall be determined in accordance with the following
formula:
( )[ ] [ ]2cc2ifrsi WAWWWWAV ++++= Where:
=V Total design base shear, N; =ci A,A Seismic accelerations
coefficients determined in accordance to Section 7.2.3;
=sW Total weight of the tank shell and appurtenances, N; =rW
Total weight of fixed tank roof including framing, knuckles, and
any
permanent attachments, as specified by the purchaser, N; =fW
Weight of tank floor, N;
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 36
=iW Effective impulsive weight of the liquid, N;
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 37
H
DH67.3sinh
DH67.3
0.1D
H67.3cosh0.1Xc
=
=isX Height from the bottom of the tank shell to the center of
action of the lateral seismic force related to the impulsive liquid
force for the slab moment, m;
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 38
=rsw Roof load acting on the shell, N/m; =vA Vertical earthquake
acceleration coefficient for self-anchored tanks;
eeyaa GDH201GHFt99w = =aw Resisting force of tank contents per
unit of shell circumference that may be
used to resist the shell overturning moment, N/m; =at Thickness
of the bottom plate under the shell extending at least the
distance, L,
from the inside of the shell, less corrosion allowance, mm; =L
Required minimum width of the bottom annulus measured from the
inside of
the shell (Defined in Section E.6.2.1.1.1 of the standard
indicates in 2.2.8), m; =yF Minimum specified yield strength of
bottom annulus, MPa; =eG Effective specific gravity including
vertical seismic effects; ( )ve A4.00.1GG = =G Specific gravity of
the product.
Table 7.1 Anchorage Ratio
Anchorage Ratio Criteria J < 0.785 No uplift under the design
seismic overturning moment. The tank is
self-anchored. 0.785 < J < 1.54 Tank is uplifting, but the
tank is stable for the design load providing the
shell compression requirements are satisfied. Tank is
self-anchored. J > 1.54 Tank is not stable and shall be
mechanically-anchored for the design
load.
7.2.7 Sliding Resistance For self-anchored flat bottom steel
tanks, the overall horizontal seismic shear force shall be resisted
by friction between the tank bottom and the foundation or subgrade.
Self-anchored storage tanks shall be designed such that sliding
will not occur where the tank is full of stored product. The
maximum calculated seismic base shear, V, does not exceed
sV : ( ) ( )vpfrss A4.00.1WWWW32.0V +++=
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 39
7.2.8 Anchorage
Experience has shown that properly designed anchored tanks
retain greater reserve strength with respect to unanchored tank.
Considering this property, tanks shall be anchored with the
exception of the tanks that fulfill the following conditions
(both):
The anchorage ratio, J, defined in Section 7.2.6, is less than
1.54. The sliding resistance, sV , defined in Section 7.2.7, is
greater than the base shear
defined in Section 7.2.4.
7.2.8.1 Anchor Bolts 7.2.8.1.1 The anchor bolt shall be of the
removable type (Type PC according the standard
indicated in 2.1.4). Therefore, the anchor bolts should take
only tensions. 7.2.8.1.2 The seismic base shear force shall be
resisted by the sliding resistance force. When
the seismic base shear exceed the sliding resistance force it
should be add stoppers or shear keys that prevents the sliding of
the tank and should be designed to resist the total base shear due
to seismic forces.
7.2.8.1.3 The anchor bolts must be designed in accordance with
the requirements of the
standard indicated in 2.2.8, Appendix E.
7.2.8.1.4 The thread length of the anchor bolt under the nut
must be longer than four nominal bolt diameters and no less than
75[mm].
7.2.8.1.5 The embedment length of the anchor bolt shall be equal
or greater than the length
recommended in the standard indicated in 2.1.4. 7.2.8.2 Anchor
Chairs 7.2.8.2.1 The anchor bolts shall have an anchor chair to
permit yielding and the inspection
of the anchors after an earthquake. 7.2.8.2.2 The anchor chair
should have a continuous upper ring along of all the perimeter
of
the tank. 7.2.8.2.3 The base plate should be dimensioned for the
bending moments coming from the
contact pressure between the bottom plate of the tank and the
foundation. The minimum dimensions should be according to the
standard indicates in 2.2.8, sections 3.4 and 3.5.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 40
7.2.8.2.4 The upper ring, the vertical stiffeners close to the
anchor bolts and the tank wall in the area of the upper ring of the
anchor chair should be able to supports the anchor attachment
design load, PA, defined in the standard indicates in 2.2.8,
section E.6.2.1.2.
7.2.8.2.5 The anchor bolt projection, measured from the top of
the tank floor plate provided
under the shell, shall be at least eight nominal diameters of
the bolt and no less than 300[mm].
7.2.8.2.6 The uncorroded thickness of the vertical chair
stiffeners must be equal or greater
than 3/8 times the thickness of the plate on the top of the
chair and no less than 10[mm]. Any specified corrosion allowance
must be added.
7.2.8.2.7 The uncorroded thickness of the upper ring plate of
the chair must be equal or
greater than 16[mm]. Any specified corrosion allowance must be
added. 7.2.8.3 Shear Device 7.2.8.3.1 Stoppers or shear keys are
device that prevents the sliding of the tank and should
be designed to resist the total base shear defined in the
section 7.2.4. 7.2.8.3.2 The stoppers should be designed to resist
a seismic force equal to a total base shear
defined in the section 7.2.4, divided by the number of stoppers
and multiplied by three. This force should be used for the
verification of welding to anchored plate and anchor stud. The
stoppers thickness should be at least fifty percent larger than
thickness of tank floor plate provided under the shell.
7.2.8.3.3 The shear keys should be located centered with respect
to the vertical tank shell. 7.2.9 Freeboard
In order to prevent the overflow of the tank contents or damages
whether to the roof or to the top of the shell, a freeboard for the
sloshing wave shall be provided. The freeboard is defined as the
distance from the maximum liquid level of the tank to the top level
of the shell. The minimum freeboard must be calculated by the
following formula:
( )D25.010.02.1
IRs +=
Where:
=s Minimum freeboard, m; =RI Hazard factor from Table 5.8; =D
Nominal tank diameter, m,
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 41
The minimum freeboard is required unless the roof and tank shell
are designed to contain the sloshing liquid.
7.2.10 Construction requirements 7.2.10.1 Annular bottom plates
shall be adopted for the design of the self-anchored tank. That
design must be in accordance with sections 3.5 and E.6.2.1.1.2
of the standard indicated in 2.2.8. Exception is made to the
requirement that the annular bottom plates shall have a minimum
radial width that provides at least 600[mm] between the inside of
the shell and any lap-welded joint in the remainder of the bottom
and at least a 50[mm] projection outside the shell.
7.2.10.2 The slope of the bottom of the tank must be in
accordance with Section B.3.3 of the
standard indicated in 2.2.8. 7.2.10.3 The connections of all
piping attached to the tank must be flexible in order to
prevent
the damage due to potential uplift or sliding of the tank during
earthquake.
Unless otherwise calculated, the following displacement shall be
assumed for the design of all side-wall connections: a. Vertical
displacement of 50[mm] for mechanically-anchored tanks. b.
Horizontal displacement for 50[mm] for mechanically-anchored tanks.
c. Vertical displacement of 300[mm] for self-anchored tanks. d.
Horizontal displacement of 200[mm] for self-anchored tanks.
7.2.10.4 The support columns of the roof and the column-base
shall be designed considering
the force due to sloshing wave. The column-base shall be
connected to the tank to prevent lateral movement of the column
bottom and the connection shall permit a vertical displacement over
the bottom of the tank equal or greater than 300[mm].
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 42
8.0 SEISMIC DESIGN OF PRESSURE VESSELS
This Section prevails over Section 11.7 of NCh 2369. 8.1 Scope
8.1.1 This standard establishes the minimum requirements for the
seismic design of vertical or
horizontal pressure vessels and of their respective support
structures, connections and anchorage systems.
8.1.2 This standard is applicable to pressure vessels whose
support system is located directly on
the ground and to pressure vessels supported on one or more
levels of the structure. 8.1.3 In the case of pressure vessels
supported on one or more levels of a structure, the seismic
load must be calculated as indicated in Section 5.4.1.1. 8.1.4
This Chapter complements the recommendations indicated in the
Chapter 5.0 of this
standard, provided that they do not contradict the
recommendations and limitations established in this Chapter.
8.2 General requirements 8.2.1 Risk classification
8.2.1.1 For seismic design, all pressure vessels shall be
classified according to the risk
classification indicated in Table 8.1. The risk grade shall be
select according to the bad conditions indicated in the Table
8.1.
Table 8.1 Risk Grade
Risk Grade
Exposed people
Direct economic loss
Indirect economic loss
Pollution
Minimum Few (20) The vessel and numerous equipment and
installation
Catastrophic Recovery greater than 3 years
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 43
8.2.1.2 When risk classification selection is unclear, the
maximum risk grade must be used. 8.2.1.3 Importance Factor
The Importance Factor shall be established according to risk
classification and the characteristics of the content. The values
of this factor correspond to those indicated in Table 5.1.
8.2.2 Combination loads 8.2.2.1 For the purpose of the pressure
vessel seismic design, the seismic loads shall be
combined with the other loads according to the ASME code. The
resulting stress shall be less than the allowable stress indicated
in the ASME code.
8.2.2.2 For the purpose of the support structure and anchorage
system seismic design, the
seismic loads shall be combined with the other loads according
to the combinations indicated in Section 3.3 and 3.4. The live
loads shall consider service and operation loads, including thermal
effects, internal pressure, eventual vibration and other effects
caused by operation.
8.2.2.3 Wind and seismic loads should not be considered to act
simultaneously. 8.2.3 Seismic loads 8.2.3.1 Seismic loads can be
specified in one of the following ways:
a. Using horizontal and vertical forces associated with the
weights of the different parts that the pressure vessel has been
divided into, for its analysis.
b. Using response spectrum for the horizontal and vertical
ground acceleration.
8.2.3.2 The pressure vessel shall be analyzed for seismic loads
acting in two horizontal directions, perpendicular to each other
and acting separately.
8.2.3.3 The analysis in one horizontal direction is only
accepted in vertical pressure vessel
with axial symmetry. 8.2.3.4 Vertical seismic loads shall be
considered in the following cases:
c. When calculating the supporting structure of the pressure
vessel. d. When calculating the anchorage system. e. When the
pressure vessel has eccentric weights or there are projecting
elements
attached to the pressure vessel.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 44
f. When calculating the pedestals and foundations. 8.2.3.5 The
seismic vertical or horizontal loads shall be assumed applied in
the most
unfavorable direction for the pressure vessels design and for
the support systems design.
8.2.3.6 The magnitude of vertical seismic loads shall be equal
to 2/3 the magnitude of
horizontal seismic loads. 8.2.4 Mathematical model of the
pressure vessel 8.2.4.1 The mathematical model used to analyze the
pressure vessel shall adequately
represent its weight and stiffness distribution and the
stiffness of supporting structure. 8.2.4.2 When partial analyses of
the pressure vessel are carried out, the mathematical model
used shall adequately represent the transfer of loads from the
points of application to the attachment and the interaction between
the parts.
8.2.4.3 The minimum number of lumped masses and degrees of
freedom to be used in the
analytical model of the pressure vessel shall be such to
reproduce the real mass distribution and the shape of the vibration
modes.
8.2.4.4 The concentrated mass model shall include all the
pressure vessel weights, the
weights of the platforms and piping attached to the pressure
vessel, the weight of the contents and the other accessories that
contribute to the weight of the structure. In pressure vessels that
contain liquids, whose volume varies according to the operating
conditions of the system, the Designer shall consider the most
probable weight of the liquid during its useful life, in according
with Section 2.1.3.
8.2.4.5 When the stiffness of the piping attached to the
pressure vessel is high, piping shall
be included in the mathematical model. 8.2.4.6 Due to physical
characteristics of the fired heaters, reactors and combined
feed
exchanger and also due to interconnecting pipes between these
equipments, Enap Refineras requires THE CONTRACTOR to carry out a
three-dimensional seismic dynamic analysis including all equipment,
piping, foundations and supporting structures.
8.2.4.7 The results of this analysis, such as the fundamental
period, forces and displacements
shall be considered for the design of equipment, interconnecting
pipe, expansion joints, springs, bumpers, stoppers, etc.
-
EI-004
WIND, EARTHQUAKE AND SNOW LOADING
Rev. 16 45
8.2.4.8 Enap Refineras will require the calculation procedure,
backup forms and the results of this analysis before placing the
purchase order of the involved equipments.
8.2.4.9 In pressure vessel that contains liquid, all the mass of
the liquid shall be assumed
rigidly attached to the pressure vessel walls. 8.2.5 Seismic
analysis
8.2.5.1 For the seismic analysis two procedures can be used:
a. Static analysis or equivalent forces analysis. b.
Dynamic-spectrum modal analysis.
8.2.5.2 Analysis of the pressure vessel shall incorporate the
horizontal and vertical
components of seismic loads acting simultaneously for the cases
indicated in Section 8.2.3.4.
8.2.5.3 The static analysis shall be used in the following
cases:
c. Rigid pressure vessels supported on ground. A pressure vessel
that has a fundamental period less than 0.06[s], including their
anchorage system, is considered rigid.
d. Flexible pressures vessel whose height is less than or equal
to 15[m] when their grade of risk is minimum or medium.
e. Pressure vessels susceptible to being reduced to
one-degree-of-freedom system.
For the others cases a dynamic spectrum modal analysis shall be
used. 8.2.5.4 The seismic force that acts on rigid pressure vessels
is calculated by multiplying their
weight by the seismic coefficient. The seismic coefficient shall
be determined according to Section 5.4.2.2. This force is assumed
to be applied at the center of gravity of the total weight of the
vessel and content.
8.2.5.5 In order to apply the static method of analysis, the
recommendations of Section 5.4.2,
shall be followed. 8.2.5.6 In order to apply the dynamic
spectrum modal analysis method, the recommendations
of Section 5.4.3