AISC LRFD 1.pdf

Comm. I5.] SHEAR CONNECTORS 227tal shear to other less heavily stressed connectors. The important consideration isthat the total number of connectors be sufficient to develop the shear V h on eitherside of the point of maximum moment. The provisions of the LRFD Specificationare based upon this concept of composite action.In computing the design flexural strength at points of maximum negative bending,reinforcement parallel to the steel beam within the effective width of the slab maybe included, provided such reinforcement is properly anchored beyond the regionof negative moment. However, enough shear connectors are required to transfer theultimate tensile force in the reinforcement, from the slab to the steel beam.3. Strength of Stud Shear ConnectorsStudies have defined stud shear connector strength in terms of normal weight andlightweight aggregate concretes as a function of both concrete modulus of elasticityand concrete strength as given by Equation I5-1.Equation I5-1, obtained from Ollgaard et al. (1971), corresponds to Tables I4.1 andI4.2 in Section I4 of the 1989 AISC ASD Specification. Note that an upper boundon stud shear strength is the product of the cross-sectional area of the stud times itsultimate tensile strength.The LRFD Specification does not specify a resistance factor for shear connectorstrength. The resistance factor for the flexural strength of a composite beamaccounts for all sources of variability, including those associated with the shearconnectors.4. Strength of Channel Shear ConnectorsEquation I5-2 is a modified form of the formula for the strength of channel connectorsdeveloped by Slutter and Driscoll (1965). The modification has extended itsuse to lightweight concrete.6. Shear Connector Placement and SpacingUniform spacing of shear connectors is permitted except in the presence of heavyconcentrated loads.Studs not located directly over the web of a beam tend to tear out of a thin flangebefore attaining full shear-resisting capacity. To guard against this contingency, thesize of a stud not located over the beam web is limited to 2 1 2 times the flange thickness(Goble, 1968).The minimum spacing of connectors along the length of the beam, in both flat soffitconcrete slabs and in formed steel deck with ribs parallel to the beam, is six diameters;this spacing reflects development of shear planes in the concrete slab(Ollgaard et al., 1971). Since most test data are based on the minimum transversespacing of four diameters, this transverse spacing was set as the minimum permitted.If the steel beam flange is narrow, this spacing requirement may be achieved bystaggering the studs with a minimum transverse spacing of three diameters betweenthe staggered row of studs. The reduction in connector capacity in the ribs offormed steel decks is provided by the factor 085 . / N r , which accounts for thereduced capacity of multiple connectors, including the effect of spacing. Whendeck ribs are parallel to the beam and the design requires more studs than can beLRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION