Consideration of Shear Stud Slip in the Design of Partially Composite Beams

Current design provisions for steel-concrete composite beams rely upon a strength-based approach as outlined by the AISC Specification. In partially composite beams, the headed stud anchors transferring interfacial shear between the concrete and steel can undergo significant slip, which is not accounted for directly in design. A numerical model was developed and benchmarked to calculate the flexural capacity of partially composite beams while accounting for slip at the steel-concrete interface. This paper presents the results of parametric studies that were conducted to evaluate the effects of various geometric and material parameters including percent composite action, beam length, and cross-section geometry. The calculated flexural capacities were compared with the corresponding nominal design strengths calculated using the AISC Specification. These comparisons indicated that longer composite beams with low degrees of composite action (of less than 50%) reached the shear connection capacity (i.e. shear connection ductility) before developing their nominal design strength as computed per the AISC Specification. This reveals the complex inter-relationship between the beam length, stud slip capacity, and the minimum level of partially composite action that may be permitted for design.