AISC LRFD 1.pdf

Comm. I4.] COMBINED COMPRESSION AND FLEXURE 225Based on the Lehigh test data (Grant et al., 1977), the maximum spacing of steeldeck anchorage to resist uplift was increased from 16 (405 mm) to 18 in. (460 mm)in order to accommodate current production profiles.When metal deck includes units for carrying electrical wiring, crossover headersare commonly installed over the cellular deck perpendicular to the ribs. They createtrenches which completely or partially replace sections of the concrete slab abovethe deck. These trenches, running parallel to or transverse to a composite beam,may reduce the effectiveness of the concrete flange. Without special provisions toreplace the concrete displaced by the trench, the trench should be considered as acomplete structural discontinuity in the concrete flange.When trenches are parallel to the composite beam, the effective flange width shouldbe determined from the known position of the trench.Trenches oriented transverse to composite beams should, if possible, be located inareas of low bending moment and the full required number of studs should beplaced between the trench and the point of maximum positive moment. Where thetrench cannot be located in an area of low moment, the beam should be designed asnon-composite.6. Design Shear StrengthA conservative approach to vertical shear provisions for composite beams isadopted by assigning all shear to the steel section web. This neglects any concreteslab contribution and serves to simplify the design.I4. COMBINED COMPRESSION AND FLEXUREThe procedure adopted for the design of beam-columns is described and supportedby comparisons with test data in Galambos and Chapuis (1980). The basicapproach is identical to that specified for steel columns in Section H1.Fig. C-I3.4. Alternative shear stud positions in rib decked profiles.LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION