Loss impact factors for lifetime seismic loss assessment of steel concentrically braced frames designed to EC8

Abstract

This study employs multiple earthquake time-history response simulations, and the FEMA P-58 performance assessment methodology to evaluate the influence of key design parameters on the lifetime seismic repair costs incurred by case study concentrically braced frames (CBFs) designed to Eurocode 8. The parameters considered include structural mass, stiffness (natural period) and ductility (behaviour factor). A new factor termed the Loss Impact Factor (LIF), is used to quantify the influence of each of these parameters on lifetime costs. Under dissipative seismic design principles, bracing members in CBFs may behave inelastically under infrequent, high-intensity earthquakes. Larger values of the design behaviour factor, q, selected by the structural engineer result in higher ductility demands during these earthquakes, but also reduce the design seismic action, leading to smaller, lighter and more flexible structural members. Hence, variations in one parameter necessarily influence the others, as well as initial construction cost. The variation in expected lifetime seismic repair costs with respect to each of these parameters, which is less clear, is the subject of this paper. Costs are shown to reduce with increased structural mass, stiffness and initial cost, with the impact of the latter two parameters generally increasing with both seismic hazard and frame height.