AISC LRFD 1.pdf

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Sect. I2.] COMPRESSION MEMBERS 41ticity for steel, E, or modulus of elasticity for concrete, E c . Concrete tensile strengthshall be neglected. Maximum stress in the steel shall not exceed F y . Maximum compressivestress in the concrete shall not exceed 0.85f c . In composite hybrid beams,the maximum stress in the steel flange shall not exceed F yf but the strain in the webmay exceed the yield strain; the stress shall be taken as F yw at such locations.Fully Composite Beam. Shear connectors are provided in sufficient numbers todevelop the maximum flexural strength of the composite beam. For elastic stressdistribution it shall be assumed that no slip occurs.Partially Composite Beam. The shear strength of shear connectors governs the flexuralstrength of the partially composite beam. Elastic computations such as thosefor deflections, fatigue, and vibrations shall include the effect of slip.Concrete-Encased Beam. A beam totally encased in concrete cast integrally withthe slab may be assumed to be interconnected to the concrete by natural bond, withoutadditional anchorage, provided that: (1) concrete cover over the beam sides andsoffit is at least two in. (50 mm); (2) the top of the beam is at least 1 1 2-in. (38 mm)below the top and two in. (50 mm) above the bottom of the slab; and (3) concreteencasement contains adequate mesh or other reinforcing steel to prevent spalling ofconcrete.Composite Column. A steel column fabricated from rolled or built-up steel shapesand encased in structural concrete or fabricated from steel pipe or HSS and filledwith structural concrete.Encased Composite Column. A steel column fabricated from rolled or built-upshapes and encased in structural concrete.Filled Composite Column. Structural steel HSS or pipes that are filled with structuralconcrete.I2. COMPRESSION MEMBERS1. LimitationsTo qualify as a composite column, the following limitations shall be met:(1) The cross-sectional area of the steel shape, pipe, or HSS shall comprise at leastfour percent of the total composite cross section.(2) Concrete encasement of a steel core shall be reinforced with longitudinalload-carrying bars, longitudinal bars to restrain concrete, and lateral ties. Longitudinalload-carrying bars shall be continuous at framed levels; longitudinalrestraining bars may be interrupted at framed levels. The spacing of ties shallbe not greater than two-thirds of the least dimension of the composite crosssection. The cross-sectional area of the transverse and longitudinal reinforcementshall be at least 0.007 sq. in. per in. (180 mm 2 per m) of bar spacing. Theencasement shall provide at least 1 1 2-in. (38 mm) of clear cover outside of bothtransverse and longitudinal reinforcement.(3) Concrete shall have a specified compressive strength f c of not less than 3 ksi(21 MPa) nor more than 8 ksi (55 MPa) for normal weight concrete and not lessthan 4 ksi (28 MPa) for light weight concrete.(4) The specified minimum yield stress of structural steel and reinforcing bars<strong>LRFD</strong> Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION
42 COMPRESSION MEMBERS [Sect. I2.used in calculating the strength of a composite column shall not exceed 60 ksi(415 MPa).(5) The minimum wall thickness of structural steel pipe or HSS filled with concreteshall be equal to b Fy /3Efor each face of width b in rectangular sectionsand D Fy /8Efor circular sections of outside diameter D.2. Design StrengthThe design strength of axially loaded composite columns is c P n ,where c = 0.85P n = nominal axial compressive strength determined from Equations E2-1through E2-4 with the following modifications:(1) A g is replaced by A s , the gross area of steel shape, pipe, or HSS, in. 2 (mm 2 )(2) r is replaced by r m , the radius of gyration of the steel shape, pipe, or HSS exceptthat for steel shapes it shall not be less than 0.3 times the overall thicknessof the composite cross section in the plane of buckling, in. (mm)(3) F y is replaced by F my , the modified yield stress from Equation I2-1F my = F y + c 1 F yr (A r / A s ) + c 2 f c (A c / A s )(I2-1)(4) E is replaced by E m , the modified modulus of elasticity from Equation I2-2.E m = E + c 3 E c (A c / A s )(I2-2)whereA c = area of concrete, in. 2 (mm 2 )A r = area of longitudinal reinforcing bars, in. 2 (mm 2 )A s = area of steel, in. 2 (mm 2 )E = modulus of elasticity of steel, ksi (MPa)E c = modulus of elasticity of concrete. E c is permitted to be computed15 .from Ec= w fc′(metric: Ec= 0 041w 15 .. fc′) where w, the unitweight of concrete, is expressed in lbs./cu. ft (kg/m 3 ) and f c is expressedin ksi (MPa).F y = specified minimum yield stress of steel shape, pipe, or HSS, ksi(MPa)F yr = specified minimum yield stress of longitudinal reinforcing bars, ksi(MPa)f c = specified compressive strength of concrete, ksi (MPa)c 1 , c 2 , c 3 = numerical coefficients. For concrete-filled pipe and HSS: c 1 = 1.0, c 2= 0.85, and c 3 = 0.4; for concrete-encased shapes c 1 = 0.7, c 2 = 0.6,and c 3 = 0.23. Columns with Multiple Steel ShapesIf the composite cross section includes two or more steel shapes, the shapes shall beinterconnected with lacing, tie plates, or batten plates to prevent buckling of individualshapes before hardening of concrete.<strong>LRFD</strong> Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION
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LOAD AND RESISTANCEFACTOR DESIGNSPE
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iiCopyright © 2000byAmerican Insti
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vTABLE OF CONTENTSSYMBOLS . . . . .
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TABLE OF CONTENTSviiSPECIFICATION (
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TABLE OF CONTENTSixSPECIFICATION (C
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TABLE OF CONTENTSxiCOMMENTARY (Cont
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SYMBOLSxviistrength (for those stee
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SYMBOLSxixS eff Effective section m
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SYMBOLSxxit s Web stiffener thickne
Page 24 and 25: xxiiiGLOSSARYAlignment chart for co
Page 26 and 27: GLOSSARYxxvEffective moment of iner
Page 28 and 29: GLOSSARYxxviiLateral bracing member
Page 30 and 31: GLOSSARYxxixPost-buckling strength.
Page 32 and 33: GLOSSARYxxxiStrain-hardening strain
Page 34 and 35: 1CHAPTER AGENERAL PROVISIONSA1. SCO
Page 36 and 37: Sect. A3.] MATERIAL 3Cold-Formed We
Page 38 and 39: Sect. A3.] MATERIAL 5ASTM A449 bolt
Page 40 and 41: Sect. A6.] REFERENCED CODES AND STA
Page 42 and 43: Sect. A7.] DESIGN DOCUMENTS 9tion A
Page 44 and 45: Sect. B4.] STABILITY 11(a) When the
Page 46 and 47: Sect. B10.] PROPORTIONS OF BEAMS AN
Page 48 and 49: Sect. B10.] PROPORTIONS OF BEAMS AN
Page 50 and 51: 17Chap. CCHAPTER CFRAMES AND OTHER
Page 52 and 53: Sect. C3.] STABILITY BRACING 19all
Page 54 and 55: Sect. C3.] STABILITY BRACING 214. B
Page 56 and 57: Sect. C3.] STABILITY BRACING 231.0;
Page 58 and 59: Sect. D3.] PIN-CONNECTED MEMBERS AN
Page 60 and 61: 27Chap. ECHAPTER ECOLUMNS AND OTHER
Page 62 and 63: Sect. E4.] BUILT-UP MEMBERS 29(a) F
Page 64 and 65: 31Chap. FCHAPTER FBEAMS AND OTHER F
Page 66 and 67: Sect. F1.] DESIGN FOR FLEXURE 33Lp=
Page 68 and 69: Sect. F2.] DESIGN FOR SHEAR 35Lpd
Page 70 and 71: 37Chap. GCHAPTER GPLATE GIRDERSI-sh
Page 72 and 73: Sect. H3.] ALTERNATIVE INTERACTION
Page 76 and 77: Sect. I3.] FLEXURAL MEMBERS 434. Lo
Page 78 and 79: Sect. I3.] FLEXURAL MEMBERS 45welde
Page 80 and 81: Sect. I5.] SHEAR CONNECTORS 47A c =
Page 82 and 83: 49Chap. JCHAPTER JCONNECTIONS, JOIN
Page 84 and 85: Sect. J1.] GENERAL PROVISIONS 518.
Page 86 and 87: Sect. J2.] WELDS 53Welding ProcessT
Page 88 and 89: Sect. J2.] WELDS 55For end-loaded f
Page 90 and 91: Sect. J2.] WELDS 57Types of Weld an
Page 92 and 93: Sect. J3.] BOLTS AND THREADED PARTS
Page 100 and 101: Sect. J4.] DESIGN RUPTURE STRENGTH
Page 102 and 103: Sect. J8.] BEARING STRENGTH 69J6. F
Page 104 and 105: 71Chap. KCHAPTER KCONCENTRATED FORC
Page 106 and 107: Sect. K1.] FLANGES AND WEBS WITH CO
Page 108 and 109: For P u 0.4P yR v = 0.60F y d c t
Page 110 and 111: Sect. K3.] DESIGN FOR CYCLIC LOADIN
Page 112 and 113: 79Chap. LCHAPTER LSERVICEABILITY DE
Page 114 and 115: 81Chap. MCHAPTER MFABRICATION, EREC
Page 116 and 117: Sect. M4.] ERECTION 83(2) Bottom su
Page 118 and 119: Sect. M5.] QUALITY CONTROL 85The fa
Page 120 and 121: Sect. N3.] EVALUATION BY STRUCTURAL
Page 122 and 123: 89App. BAPPENDIX BDESIGN REQUIREMEN
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App. B5.] LOCAL BUCKLING 914kc=h/tw
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App. B5.] LOCAL BUCKLING 93é0.877
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App. E3.] DESIGN COMPRESSIVE STRENG
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App. F1.] DESIGN FOR FLEXURE 97For
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App. F1.] DESIGN FOR FLEXURE 99TABL
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App. F1.] DESIGN FOR FLEXURE 101Cri
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App. F3.] WEB-TAPERED MEMBERS 103j
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App. F3.] WEB-TAPERED MEMBERS 105Fw
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107App. GAPPENDIX GPLATE GIRDERSThi
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App. G3.] DESIGN SHEAR STRENGTH 109
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App. G5.] FLEXURE-SHEAR INTERACTION
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App. H3.] ALTERNATIVE INTERACTION E
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115App. JAPPENDIX JCONNECTIONS, JOI
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App. J3.] BOLTS AND THREADED PARTS
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App. K2.] PONDING 119æçMetric:lC
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App. K3.] DESIGN FOR CYCLIC LOADING
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NUMERICAL VALUES 141TABLE 2ItemShap
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NUMERICAL VALUES 143Klr123456789101
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NUMERICAL VALUES 145TABLE 3-50Desig
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NUMERICAL VALUES 147TABLE 4Values o
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NUMERICAL VALUES 149TABLE 5 (cont
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NUMERICAL VALUES 151TABLE 7Values o
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NUMERICAL VALUES 153f vVAwnTABLE 8-
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NUMERICAL VALUES 157hf vVAwnTABLE 9
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NUMERICAL VALUES 161ht wf vVAwnTABL
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163COMMENTARYon the Load and Resist
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Comm. A2.] TYPES OF CONSTRUCTION 16
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Comm. A3.] MATERIAL 167and Chen, 19
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Comm. A3.] MATERIAL 169than the ant
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Comm. A4.] LOADS AND LOAD COMBINATI
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Comm. A5.] DESIGN BASIS 173where =
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Comm. A5.] DESIGN BASIS 175( )bsln(
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177Comm. BCHAPTER BDESIGN REQUIREME
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Comm. B5.] LOCAL BUCKLING 179(c) Al
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Comm. B5.] LOCAL BUCKLING 181load.
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Comm. B7.] LIMITING SLENDERNESS RAT
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Comm. C1.] SECOND ORDER EFFECTS 185
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Comm. C1.] SECOND ORDER EFFECTS 187
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Comm. C2.] FRAME STABILITY 189Buckl
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Comm. C2.] FRAME STABILITY 191Notes
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Comm. C2.] FRAME STABILITY 193Where
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Comm. C3.] STABILITY BRACING 195age
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Comm. C3.] STABILITY BRACING 197pla
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Comm. C3.] STABILITY BRACING 199The
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Comm. C3.] STABILITY BRACING 201Par
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203Comm. ECHAPTER ECOLUMNS AND OTHE
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Comm. E4.] BUILT-UP MEMBERS 205TABL
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Comm. F1.] DESIGN FOR FLEXURE 207ha
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Comm. F1.] DESIGN FOR FLEXURE 2092b
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Comm. F4.] BEAMS AND GIRDERS WITH W
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Comm. H2.] UNSYMMETRIC MEMBERS AND
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Comm. I2.] COMPRESSION MEMBERS 215d
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Comm. I3.] FLEXURAL MEMBERS 217may
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Comm. I3.] FLEXURAL MEMBERS 219The
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Comm. I3.] FLEXURAL MEMBERS 221wher
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Comm. I3.] FLEXURAL MEMBERS 223proc
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Comm. I4.] COMBINED COMPRESSION AND
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Comm. I5.] SHEAR CONNECTORS 227tal
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229Comm. JCHAPTER JCONNECTIONS, JOI
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Comm. J1.] GENERAL PROVISIONS 231 P
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Comm. J2.] WELDS 2332b. Limitations
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Comm. J2.] WELDS 235When longitudin
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Comm. J2.] WELDS 237due to cyclic f
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Comm. J2.] WELDS 239(b) Plane 2-2,
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Comm. J3.] BOLTS AND THREADED PARTS
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Comm. J4.] DESIGN RUPTURE STRENGTH
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249Comm. KCHAPTER KCONCENTRATED FOR
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Comm. K1.] FLANGES AND WEBS WITH CO
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Comm. K1.] FLANGES AND WEBS WITH CO
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Comm. K2.] PONDING 255Even on the b
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257Comm. LCHAPTER LSERVICEABILITY D
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Comm. L5.] CORROSION 259orthotropic
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Comm. M4.] ERECTION 261It is sugges
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Comm. N4.] EVALUATION BY LOAD TESTS
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Comm. N5.] EVALUATION REPORT 265N5.
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267Comm. A-EAPPENDIX ECOLUMNS AND O
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Comm. App. F3.] WEB-TAPERED MEMBERS
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271Comm. A-GAPPENDIX GPLATE GIRDERS
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273Comm. A-KAPPENDIX JCONNECTIONS,
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Comm. J2.] WELDS 275found to be con
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Comm. K3.] DESIGN FOR CYCLIC LOADIN
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279ReferencesAckroyd, M. H., and Ge
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REFERENCES 281Bjorhovde, R. (1972),
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REFERENCES 283Fielding, D. J., and
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REFERENCES 285Johnson, D. L. (1985)
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REFERENCES 287Ollgaard, J. G., Slut
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REFERENCES 289Zhou, S. P., and Chen
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SUPPLEMENTARY BIBLIOGRAPHY 291Kotec
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Metric Conversion Factors for Commo
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