Proposed nonlinear macro‐model for seismic risk assessment of composite‐steel moment resisting frames

Abstract

AbstractThis 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.