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Comm. K2.] PONDING 255Even on the basis of unlimited elastic behavior, it is seen that the ponding deflectionswould become infinitely large unlessSince elastic behavior is not unlimited, the effective bending strength available ineach member to resist the stress caused by ponding action is restricted to the differencebetween the yield stress of the member and the stress f o produced by the totalload supported by it before consideration of ponding is included.Note that elastic deflection is directly proportional to stress. The admissible amountof ponding in either the primary or critical (midspan) secondary member, in termsof the applicable ratio w / o and w / o , can be represented as (F y – f o )/f o . Substitutingthis expression for w / o and w / o , and combining with the foregoingexpressions for w and w , the relationship between critical values for C p and C s andthe available elastic bending strength to resist ponding is obtained. The curvespresented in Figures A-K2.1 and A-K2.2 are based upon this relationship. Theyconstitute a design aid for use when a more exact determination of required flatroof framing stiffness is needed than given by the LRFD Specification provisionthat C p + 0.9C s 0.25.Given any combination of primary and secondary framing, the stress index is computedasUp⎛ F= ⎜⎝y− ffooæ Cpöæ C ösç1 C÷ç
256 PONDING [Comm. K2.would be determined by the intercept of a horizontal line representing the U s valueand the curve for C p = 0.The ponding deflection contributed by a metal deck is usually such a small part ofthe total ponding deflection of a roof panel that it is sufficient merely to limit itsmoment of inertia [in. 4 per foot (mm 4 per meter) of width normal to its span] to0.000025 (3 940) times the fourth power of its span length, as provided in the LRFDSpecification. However, the stability against ponding of a roof consisting of a metalroof deck of relatively slender depth-span ratio, spanning between beams supporteddirectly on columns, may need to be checked. This can be done using FigureA-K2.1 or A-K2.2 with the following computed values:U p = stress index for the supporting beamU s = stress index for the roof deckC p = flexibility constant for the supporting beamsC s = flexibility constant for one foot width of the roof deck (S = 1.0)Since the shear rigidity of the web system is less than that of a solid plate, themoment of inertia of steel joists and trusses should be taken as somewhat less thanthat of their chords.LRFD 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
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xxiiiGLOSSARYAlignment chart for co
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GLOSSARYxxvEffective moment of iner
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GLOSSARYxxviiLateral bracing member
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GLOSSARYxxixPost-buckling strength.
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GLOSSARYxxxiStrain-hardening strain
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1CHAPTER AGENERAL PROVISIONSA1. SCO
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Sect. A3.] MATERIAL 3Cold-Formed We
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Sect. A3.] MATERIAL 5ASTM A449 bolt
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Sect. A6.] REFERENCED CODES AND STA
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Sect. A7.] DESIGN DOCUMENTS 9tion A
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Sect. B4.] STABILITY 11(a) When the
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Sect. B10.] PROPORTIONS OF BEAMS AN
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Sect. B10.] PROPORTIONS OF BEAMS AN
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17Chap. CCHAPTER CFRAMES AND OTHER
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Sect. C3.] STABILITY BRACING 19all
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Sect. C3.] STABILITY BRACING 214. B
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Sect. C3.] STABILITY BRACING 231.0;
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Sect. D3.] PIN-CONNECTED MEMBERS AN
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27Chap. ECHAPTER ECOLUMNS AND OTHER
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Sect. E4.] BUILT-UP MEMBERS 29(a) F
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31Chap. FCHAPTER FBEAMS AND OTHER F
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Sect. F1.] DESIGN FOR FLEXURE 33Lp=
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Sect. F2.] DESIGN FOR SHEAR 35Lpd
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37Chap. GCHAPTER GPLATE GIRDERSI-sh
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Sect. H3.] ALTERNATIVE INTERACTION
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Sect. I2.] COMPRESSION MEMBERS 41ti
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Sect. I3.] FLEXURAL MEMBERS 434. Lo
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Sect. I3.] FLEXURAL MEMBERS 45welde
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Sect. I5.] SHEAR CONNECTORS 47A c =
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49Chap. JCHAPTER JCONNECTIONS, JOIN
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Sect. J1.] GENERAL PROVISIONS 518.
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Sect. J2.] WELDS 53Welding ProcessT
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Sect. J2.] WELDS 55For end-loaded f
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Sect. J2.] WELDS 57Types of Weld an
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Sect. J3.] BOLTS AND THREADED PARTS
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Sect. J4.] DESIGN RUPTURE STRENGTH
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Sect. J8.] BEARING STRENGTH 69J6. F
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71Chap. KCHAPTER KCONCENTRATED FORC
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Sect. K1.] FLANGES AND WEBS WITH CO
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For P u 0.4P yR v = 0.60F y d c t
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Sect. K3.] DESIGN FOR CYCLIC LOADIN
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79Chap. LCHAPTER LSERVICEABILITY DE
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81Chap. MCHAPTER MFABRICATION, EREC
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Sect. M4.] ERECTION 83(2) Bottom su
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Sect. M5.] QUALITY CONTROL 85The fa
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Sect. N3.] EVALUATION BY STRUCTURAL
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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
Page 238 and 239: Comm. E4.] BUILT-UP MEMBERS 205TABL
Page 240 and 241: Comm. F1.] DESIGN FOR FLEXURE 207ha
Page 242 and 243: Comm. F1.] DESIGN FOR FLEXURE 2092b
Page 244 and 245: Comm. F4.] BEAMS AND GIRDERS WITH W
Page 246 and 247: Comm. H2.] UNSYMMETRIC MEMBERS AND
Page 248 and 249: Comm. I2.] COMPRESSION MEMBERS 215d
Page 250 and 251: Comm. I3.] FLEXURAL MEMBERS 217may
Page 252 and 253: Comm. I3.] FLEXURAL MEMBERS 219The
Page 254 and 255: Comm. I3.] FLEXURAL MEMBERS 221wher
Page 256 and 257: Comm. I3.] FLEXURAL MEMBERS 223proc
Page 258 and 259: Comm. I4.] COMBINED COMPRESSION AND
Page 260 and 261: Comm. I5.] SHEAR CONNECTORS 227tal
Page 262 and 263: 229Comm. JCHAPTER JCONNECTIONS, JOI
Page 264 and 265: Comm. J1.] GENERAL PROVISIONS 231 P
Page 266 and 267: Comm. J2.] WELDS 2332b. Limitations
Page 268 and 269: Comm. J2.] WELDS 235When longitudin
Page 270 and 271: Comm. J2.] WELDS 237due to cyclic f
Page 272 and 273: Comm. J2.] WELDS 239(b) Plane 2-2,
Page 274 and 275: Comm. J3.] BOLTS AND THREADED PARTS
Page 280 and 281: Comm. J4.] DESIGN RUPTURE STRENGTH
Page 282 and 283: 249Comm. KCHAPTER KCONCENTRATED FOR
Page 284 and 285: Comm. K1.] FLANGES AND WEBS WITH CO
Page 286 and 287: Comm. K1.] FLANGES AND WEBS WITH CO
Page 290 and 291: 257Comm. LCHAPTER LSERVICEABILITY D
Page 292 and 293: Comm. L5.] CORROSION 259orthotropic
Page 294 and 295: Comm. M4.] ERECTION 261It is sugges
Page 296 and 297: Comm. N4.] EVALUATION BY LOAD TESTS
Page 298 and 299: Comm. N5.] EVALUATION REPORT 265N5.
Page 300 and 301: 267Comm. A-EAPPENDIX ECOLUMNS AND O
Page 302 and 303: Comm. App. F3.] WEB-TAPERED MEMBERS
Page 304 and 305: 271Comm. A-GAPPENDIX GPLATE GIRDERS
Page 306 and 307: 273Comm. A-KAPPENDIX JCONNECTIONS,
Page 308 and 309: Comm. J2.] WELDS 275found to be con
Page 310 and 311: Comm. K3.] DESIGN FOR CYCLIC LOADIN
Page 312 and 313: 279ReferencesAckroyd, M. H., and Ge
Page 314 and 315: REFERENCES 281Bjorhovde, R. (1972),
Page 316 and 317: REFERENCES 283Fielding, D. J., and
Page 318 and 319: REFERENCES 285Johnson, D. L. (1985)
Page 320 and 321: REFERENCES 287Ollgaard, J. G., Slut
Page 322 and 323: REFERENCES 289Zhou, S. P., and Chen
Page 324 and 325: SUPPLEMENTARY BIBLIOGRAPHY 291Kotec
Page 326 and 327: Metric Conversion Factors for Commo
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