Egyptain code S of practice for steel CONSTRUCTION

EGYPTAIN CODES OF PRACTICE FOR STEEL CONSTRUCTION(LRFD & ASD) IN A COPMUTER PROGRAM FORM

N. S. Mahmoud1, E. S. Aguib2, F. A. Salem3 & S. S. Abed-elaal3

ABSTRACT

Civil and structural engineers attempt to improve the analysis and design of structural systems. On the way of development of codes, methods of design should be improved. Development of codes increases equations, factors, parameters which are control the design. More factors as (Lu, Fltb, Cb, Cm, M, Q, Steel grade, etc.) have effects on the design [1], [2], [3]. [4]& [5]. Choice of sections by empirical methods or by experience is possiblebut it dose not give the economic design. To obtain the economic design, engineers should do many trails. Steel -I- section may have a large inertia but it may be aslender section and its properties must be reduced. On adverse the section may have a small inertia but it is a compact section and it has a high allowable stress. Very important questions needed to be answered; which section is more economic? Which factors have more effect on the design? How designers can get economic design?The main aim of the present paper is to get answer for theprevious questions. This research introduces a computerprogram to help designers to find economic designs fordifferent steel elements. This program has intelligentcriteria to find the best design, based on Egyptian CodesASD [6] or LRFD [7], under different conditions and give acomplete calculation sheets in few minutes.

INTRODUCTIONThere are many programs used for analysis and design ofsteel structures such as; COSMOS, STAAD, ANSYS, SAP and

etc. These programs based on popular international codesfor countries such as Australia, People’s Republic ofChina, Eastern Europe, Japan, Western Europe, USA andCanada [1], [8], [9] & [10]. It is necessary to develop aprogram following the Egyptian codes; in this program weachieve immediately the most economic design, making allthe necessary checks. The program based on Visual Basic[11] & [12]

1-Professor, 2- Associated Professor, 3- Assistant ProfessorStr. Eng. Dept., Faculty of Engineering, Mansoura University, Mansoura, Egypt e-mail : [email protected]

1. Elements which can be designed (ASD [6] or LRFD [7]) bythe present computer program:

1-1- I- beams 1-2- I-compression members 1-3- I- beam-column members1-4-Plate girders 1-5-Truss members ( one angle, two angles, tee sections,

channel, pipe) 1-6-Bolted connections with non-pretension bolts of the

bearing type1-7-High strength pretension bolted connections of the

friction type1-8-Bolted splices1-9-Composite beams and shear connectors (stud type).1-10- Cold formed sections

2. Elements which are not covered by the computer program2-1-Plate girder stiffeners2-2-Truss bridges2-3-Composite columns2-4-Composite beam-columns2-5-Shear connectors except stud type

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2-6- Built-up columns with lattice bar or batten plates

3. Main form in the programForm in figure 1 is the main form in the program whichleads to all internal forms and using it, engineer canselect the code (ASD [6] or LRFD [7]) and the elementswhich will be designed.The main form components (Figure 1) are:

3.1Design of beams, columns & beam-columns.3.2Design of different connections 3.3Design of composite beams.3.4Design of truss members.3.5Design of cold formed sections.

4. Charts for design of I-beams.

4.1. Introduction Spacing of lateral bracing at distance greater than Lp creates a problem in which the designer is confronted with a given laterally un-braced length (usually less than the total span) along the compression flange, and a calculated required bending moment.The beam cannot be selected from its plastic section modulus alone, since depth, flange proportions, and otherproperties have an influence on its bending strength, given charts solve these problems, these charts were prepared by the assistance of the developed program.

4.2 Charts for design of rolled I-beams according to LRFD [7].

The charts give the design moments bMn for HEB, SIB andIPE shapes from ST37 (Fy=2.4t/cm2 ), ST44 (Fy=2.8t/cm2 )and ST52 ( Fy=3.6t/cm2 ), used as beams, with respect to the maximum un-braced length for which this moment is permissible in bending, (b = 0.85). Charts extend over varying un-braced length, depending upon the flexural strengths of beams represented. The design moment (bMn m.t) is plotted with respect to the un-braced length with no consideration of the moment dueto weight of the beam. These moments are shown for un-

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braced lengths starting at spans less than Lp, for spans between Lp and Lr and for spans beyond Lr.The un-braced length Lp in m, with the limit indicated bya solid symbol,, is the maximum un-braced length of the compression flange, with Cb =1.0 and for which the designmoment is given by bMn. Where Un-braced length Lp is computed using equation 5.4 [7]LP=

80ry√Fyf

5.4

, and un-braced length Lr shall be computed usingequation 5.7 [7]

Lr=1380AfdFL √12 (1+√1+(2XFL )2)5.7

For compact sections with the un-braced length notgreater than Lp, in these cases Mn is computed fromequation 5.3[7], where Mp= FyZ≤ 1.5 My.Mn=Mp 5.3

For compact sections with the un-braced length greater than Lp and not exceed than Lr , Mn is computed from equation5.6 [7]

Mn=[Mp− (Mp−Mr ){Lb−LpLr−Lp }]Cb≤M 5.6

For compact sections with the un-braced length greater than Lr, Mn is computed from equation 5.12 [7]

Mcr=Sx√(1380AfdLb )2

+(20700(LbrT)2 )

2≤ 5.12

For non-compact sections with un-braced length notgreater than Lp

' in these cases Mn is computed from

equation 5.16 [7]

Mn=[Mp− (Mp−Mr ){ λ−λpλr−λp }]≤Mp 5.16

and Lp' is computed from equation 5.17 [7]

L'p=[Lp +(Lr−Lp ){Mp−MnMp−Mr }]5.17

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For non-compact sections with un-braced length greaterthan Lp

' and not exceed than Lr, in these cases Mn is the

smaller of equation 5.6 [7] and 5.16 [7].For non-compact sections with the un-braced lengthgreater than Lr, in these cases Mn is computed fromequation 5.16 [7]

The un-braced length Lr limit indicated by an open symbolo, is the maximum untraced length.The un-braced length in the charts (figure 2) may be either the total span or any part of the total span between braced points, the plots shown in these charts were computed for beams for which Cb=1.0. When a moment gradient exists between point of bracing, Cb may be larger than unity. Using this larger value of Cb may provide a more liberal flexural strength for the sectionchosen.In computing the points for the curves, Cb in the above formulas was taken as unity, E=2100 t/cm2 and G=810 t/cm2. The beam strength has been reduced by multiplying the nominal flexural strength Mn by 0.85, the resistance factor b for flexural. Over a limited range of length, agiven beam is the lightest available for various combinations of un-braced length and design moment. The charts are designed to assist in the selection of the lightest available beam for the given combination. The curves are plotted without regard to shear strength and deflection criteria, therefore due care must be exercised in their use. The following examples illustrate the use of the charts.

4.3 Example to explain using the chartsGiven: A “fixed end” girder with a span of 18 m supports

a concentrated load at the centre. The compression flange is laterally supported at the concentrated load point and at the inflection points. The factored load produced a maximum calculated moment

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of 61.0 m.t. at the load point and supports. Determine the size of the beam using ST52 (Fy = 3.6t/cm2).

Solution: For this loading condition, Cb =1.67, with

an un-braced length of 4.5 m. With the total span

equal to 18 m and Mu =61.0 m.t, assume approximate

weight of beam at 70 kg/m

Total Mu=61.00 + [0.07x(18)2

24x1.2]= 62.13 m.t at the centre

line and 63.268 m.t at the support. Compute Mequiv bydividing the required design moment by Cb. Mequiv=63.268/1.67=37.9 m.tEnter charts with un-braced length equal to 4.5 m and proceed upward to 37.9 m.t .Any beam listed above and to the right of the point satisfies the design moment.The lightest section satisfying the criteria of a design moment of 37.9 m.t at an un-braced length of4.5 m and bMp greater than 63.268 m.t is an IPE 500x90.7 as shown in (figure 3-a) and (figure 3-b).The design moment for an IPE 500x90.7 with an un-braced length of 4.5m is 51.78 m.t and bMp is 69.4 m.tSince (bMn = 51.78 m.t) > (Mequiv = 37.9 m.t) and (bMp = 69.4 m.t)> (Mu = 63.268 m.t) then IPE 500 iso.k.

5 CONCLUSIONS

1. It is impressive in the present design program to let the program to achieve immediately the most economic design using intelligent criteria where optimization is considered, making all necessary checks needed to satisfy the E.C.P. [7]. The present program makes operation of

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design of steel structure simpler, it helps the designers to complete design in few seconds. 2. Putting code equations in form of computer programs is very important to find any effect in these equations at any case of design.3. It is very useful to making computer programs to compare between methods of design for different codes.4. The designers can use these programs to determine the best economic design in less time, using these programs isa simple way to reach the best design.5. Engineers can design -I- beam rolled sections and get the economic design using simple charts.

6 NOTATIONS

Af Area of compression flange, cm2

Cb Bending coefficient depending on momentgradient.

Cm Coefficients applied to bending term ininteraction formula

d Total depth of the beam, cmFL Residual stress = 0.75 Fy for rolled sections,

t/cm2

Fltb Allowable lateral torsional buckling stress,t/cm2

Fy Specified yield stress, t/cm2

G Shear modulus, t/cm2

Lb Distance between points braced against lateraldisplacement of the compression flange, orbetween points braced to prevent twist of thecross sections. cm

Lp Limiting laterally un-braced length for fullplastic bending capacity, cm

Lr Limiting laterally un-braced length forinelastic lateral torsional buckling, cm

Lu Effective lateral unsupported length of thecompression flange, cm

M Bending moment, cm.tMn Nominal flexural strength, cm.tMp Plastic moment, cm.t

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Mu Required flexural strength, cm.tMy Yield moment, cm.trT Radius of gyration about the minor axis of a

section comprising the compression flange plusone sixth of the web area, cm

ry Radius of gyration about minor principle axis,cm

S Elastic section modulus, cm3

Z Plastic section modulus, cm3

λ Controlling slenderness parametersλp Limiting width-thickness ratio for compact

flangeLimiting depth-thickness ratio for compact web

λr Limiting width-thickness ratio for non-compactflangeLimiting depth-thickness ratio for web noncompact web

b Flexural resistance factor

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Fig.1 Main form

6 REFERENCES

[1] American Institutes of Steel Construction. (1999).

"Load and Resistance Factor Design Specification for

Structural Steel Buildings”, Chicago, Illinois, USA.

[2] Basic Wiring (Sunset New Basic) by Sunset Books

(Paperback - Mar 1995).

[3] “COLD-FORMED-STEEL DESIGN AND CONSTRUCTION”. By

Consulting Engineer, Middletown, Ohio

[4] Comprehensive DESIGN OF STEEL STRUCTURES By Dr. B.C.

PUNMIA B.E. (Hons.), M.E. (Hons.), Ph. Formerly, PROFESSOR

& HEAD, DEPARTMENT OF CIVIL ENGINEERING & DEAN, FACULTY OF

ENGINEERING M.B.M. ENGINEERING COLLEGE, JODHPUR ASIIOK

KUMAR JAIN, CONSULTING ENGINEER, ARUN KUMAR JAIN,

ASSISTANT PROFESSOR OF CIVIL ENGINEERING, M.B.M.

ENGINEERING COLLEGE, JODHPUR, IN SI UNITS, Copy 1995,1998.

[5] Steel Designer Handbook “LRFD METHOD”. By AKBAR

R.Tamboil P.E. FASCE Consulting Engineer Princeton, New

Jersey, copyright 1997 by The McGraw-Hill Companies.

[6] Egyptian code of practice for steel construction and

bridges (allowable stress design) Code No. (205)-

Ministerial Decree No. 279-2001- first edition 2001.

[7] Egyptian code of practice for steel construction (load

and resistance factor design) Code No. (205)- Ministerial

Decree No. 359-2007- first edition 2008.

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[8] Euro code 3,"Design of Steel Structures", ENV 1993

PART 1.1, and General Rules for Buildings. European

Committee for Standardization, Brussels.

[9] MANUAL OF STEEL CONSTRUCTION, LOAD & RESISTANCE

FACTOR, DESIGN Volume I, Structural Members,

Specifications, Codes. Copyright 1994.

[10] Ravindra, M. K. and Galambos, T. V. Load and

resistance factor design for steel. Proceedings American

Society of Civil Engineers, 104 (ST9), September 1978. pp

1337-1353.

[11] Programming with Visual Basic 6.0: An Object-Oriented

Approach - Introductory by Michael V. Ekedahl and William

A. Newman (Paperback - Jan 29, 1999).

[12] Security for Microsoft Visual Basic .NET by Ed

Robinson and Michael James Bond (Paperback - May 28,

2003).

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Fig.2 some charts for design of rolled I- beams according to LRFD [7]

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Fig. (3-a)Chart for design of rolled I- beams according to LRFD [7]

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Fig. (3-b)Chart for design of rolled I- beams according to LRFD [7]

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