Influence of Seismic Design Evolution on the Seismic Collapse Behavior and Losses of Prototype Steel Buildings with Moment-Resisting Frames

Abstract

Seismic design provisions for steel moment frame buildings have undergone substantial changes over the past half century. Despite the anticipated benefits of enforcing newer codes, it is not yet fully known how the evolution of seismic provisions has changed the risk associated with steel moment frame use. To address this shortcoming, a seismic loss assessment is performed for two-, four, and eight-story prototype steel moment frames designed using seismic provisions from three eras spanning the past half century. Frames of different vintages differ significantly in material properties, welding practices, connection types, seismic lateral force used for design, and panel zone design philosophy. High-fidelity models capable of explicitly capturing instabilities and fracture are employed to determine the effect of the differences in these designs. The simulation results show that although the collapse risk decreased as the codes evolved, the collapse probability of frames designed to the latest specifications still exceed the expected norms. Analysis of the four-story frames showed that the effect of brittle fracture in the welds of pre-Northridge connections on frame collapse capacity is modest. However, it is quite influential on economic and social losses for the level of seismic hazard considered. The assessment results are used to propose strategies for reducing the seismic losses of communities with steel buildings.