AISC LRFD 1.pdf

Sect. K3.] DESIGN FOR CYCLIC LOADING (FATIGUE) 77(1) The thickness and extent of the doubler plate shall provide the additional materialnecessary to equal or exceed the strength requirements.(2) The doubler plate shall be welded to develop the proportion of the total forcetransmitted to the doubler plate.K2. PONDINGThe roof system shall be investigated by structural analysis to assure adequatestrength and stability under ponding conditions, unless the roof surface is providedwith sufficient slope toward points of free drainage or adequate individual drains toprevent the accumulation of rainwater.The roof system shall be considered stable and no further investigation is needed if:C p + 0.9C s 0.25(K2-1)whereCp32LL=104s p7Ip⎛Metric : C⎜⎝432SLsCs=710 Isp4504LL⎞s p=I ⎟p ⎠I d 25(S 4 )10 -6 (K2-2)(Metric: I d 3 940 S 4 )(K2-2M)4⎛504SL⎞s⎜Metric : Cs= ⎟⎝Is⎠L p = column spacing in direction of girder (length of primary members), ft (m)L s = column spacing perpendicular to direction of girder (length of secondarymembers), ft (m)S = spacing of secondary members, ft (m)I p = moment of inertia of primary members, in. 4 (mm 4 )I s = moment of inertia of secondary members, in. 4 (mm 4 )I d = moment of inertia of the steel deck supported on secondary members, in. 4 perft (mm 4 per m)For trusses and steel joists, the moment of inertia I s shall be decreased 15 percentwhen used in the above equation. A steel deck shall be considered a secondarymember when it is directly supported by the primary members.See Appendix K2 for an alternate determination of flat roof framing stiffness.K3. DESIGN FOR CYCLIC LOADING (FATIGUE)Few members or connections in conventional buildings need to be designed forLRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION