Publication
This paper proposes a macro-model for simulating the hysteretic behavior of composite-steel beams as part of fully restrained beam-to-column connections in composite-steel moment-resisting frames (MRFs). Comparisons with experimental data suggest that the proposed model captures the asymmetric hysteretic response of composite-steel beams including the cyclic deterioration in strength and stiffness. Moreover, the proposed model captures the primary slab-column force transfer mechanisms and predicts the slip demands in beam-slab connections under inelastic cyclic loading. The modeling approach is employed in a system-level study to benchmark the seismic collapse risk of composite-steel MRF buildings across Europe. Moreover, the beam-slab slip demands are quantified through the development of beam-slab slip hazard curves. The simulation studies suggest that the examined composite-steel MRFs exhibit a system overstrength of about 4. This is attributed to the drift requirements in the current European seismic provisions.(1) The annualized probability of collapse of the prototype buildings is well below 1% over a 50-year building life expectancy regardless of the design site and the degree of composite action. Beam-slab connections with a partial degree of composite action experience minimal damage for frequently occurring seismic events (i.e., 50% probability of exceedance over 50 years); and light cracking in the slab for a design basis earthquake. The above are important from a seismic repairability standpoint. Accordingly, it is recommended that the 25% reduction in the shear resistance of stud connectors is not imperative for seismic designs that feature steel beams with depths less than 500 mm.