Hysteretic Behavior of Moment-Resisting Frames Considering Slab Restraint and Framing Action

Abstract

This paper examines the influence of framing action and slab continuity on the hysteretic behavior of composite steel moment-resisting frames (MRFs) by means of high-fidelity continuum finite-element (CFE) analyses of two-bay subsystems and typical cruciform subassemblies. The CFE model, which is made publicly available, was thoroughly validated with available full-scale experiments and considers variations in the beam depth and the imposed loading history. The simulation results suggest that beams in subsystems may experience up to 25% less flexural strength degradation than those in typical subassemblies. This is because of local buckling straightening from the slab continuity and framing action evident in subsystems. For the same reason, beam axial shortening attributable to local buckling progression is up to five times lower in subsystems than in subassemblies, which is consistent with field observations. While the hysteretic behavior of interior panel zone joints is symmetric, exterior joint panel zones in subsystems experience large asymmetric shear distortions regardless of the employed lateral loading history. From a design standpoint, it is found that the probable maximum moment in deep and slender beams (db≥700 mm) may be up to 25% higher than that predicted by current design provisions with direct implications to capacity design of steel MRFs. The 25% reduction in the shear stud capacity as proposed by current seismic provisions is not imperative for MRFs comprising intermediate to shallow beams and/or featuring a high degree of composite action (η>80%) as long as ductile shear connectors are employed.