Seismic performance evaluation of high-post-yield stiffness concentrically braced steel frames under mainshock-consistent-aftershock sequences

Abstract

Structures may be subjected to earthquake sequences after major mainshock (MS) events in seismically active sites within a short time. As a result, they may be susceptible to damage accumulation, which may hinder their performance under consecutive seismic loading. This study evaluates the effects of earthquake sequences on the seismic performance of seismic-resistant concentrically braced steel frames designed to Eurocode-8. The frames under investigation have concentric chevron-type braces with replaceable hourglass-shaped pins made of duplex stainless steel. The seismic energy is dissipated through inelastic deformations concentrated in the pins while keeping the other members elastic. The stainless-steel pins provide the frame with high-post-yield stiffness to reduce the residual drifts after a seismic event. The seismic behaviour of the frame is assessed using site hazard-specific mainshock-consistent-aftershock (MS-AS) sequences selected for a site in Terni, Central Italy. Nonlinear back-to-back dynamic analyses are performed at multiple intensity levels while adopting detailed numerical nonlinear models created in OpenSees. We show that the implemented behaviour factor satisfies the life safety assurance objective while keeping the maximum residual inter-storey drifts below 1/300 to permit an easy substitution of the damaged pins after the design-level earthquake without being curtailed by the potential following events. We then develop prediction models for the damage accumulation in the pins, considering different energy-based intensity measures and we show that the cumulative absolute velocity-based model is the most efficient predictor in this particular case. Finally, the damage accumulation in the pins is evaluated, confirming their superior low-cycle fatigue capacity under earthquake sequences.