Seismic behavior of steel building structures with composite slabs

As part of the activities of the steel structure phase of the U.S.-Japan Cooperative Earthquake Research Program Utilizing Large-Scale Facilities, experimental and analytical studies of full-scale composite beam-to-column joints and of a 0.305 scale model of the six-story prototype steel building structure have been carried out. The objectives are (i) to investigate the effect of composite slabs on the seismic characteristics of the composite beam-to-column joints and their structural elements as well as the interaction between the elements, (ii) to search for mathematical models of composite beams and composite beam-to-column joint panel zones for the purpose of the inelastic analysis of steel building structures with composite slabs, and (iii) to study the lateral load-deformation response of a dual lateral force-resisting bracing system consisting of a concentrically braced frame and two moment-resisting frames and the feasibility of a quasi-static test method in study of structural response to earthquake ground excitations.; Three types of composite beam-to-column joints, one interior and two exterior, have been tested with displacement-controlled cyclic loading. A two-step analysis approach using finite element methods is proposed to analyze the load-deformation behavior and the results are compared with the tests. Mathematical models of composite beams and composite beam-to-column joint panel zones have been developed by parametric studies.; The major findings are summarized as follows: (1) Increase in the stiffness and strength of composite beams due to composite slab is substantial. (2) Composite beam-to-column joint panel zones showed excellent seismic behavior with high reserve strength beyond yielding. (3) Essentially two types of joint behavior have been found. The joint with substantial shear yielding of the panel zone showed good ductility. On the other hand, the full beam strength did develop in the joint with a relatively stiff and strong panel zone, but its ductility was impaired by flange local buckling or fracture. (4) The proposed analytical (hysteretical) models for the two structural elements adequately take into account the effect of composite slab on cyclic behavior. (5) The strength of a dual lateral force-resisting bracing system is limited by the strength of the braces. (6) The hysteresis loops of the joints assemblages and of the overall structure were stable and repetitive. (Abstract shortened with permission of author.)...