EAPSI:Seismic performance of vintage Japanese braced-frame buildings before and after retrofit

Sen Andrew D, Seattle WA

Investigators

Abstract

Concentrically braced frames (CBFs) are commonly used in steel buildings in the US and Japan to resist earthquake-induced forces. Many CBFs that remain in use today were designed prior to the late 1980s, when design focused on strength and stiffness. Seismic provisions at the time implied buildings could sustain inelastic (permanent) deformations while maintaining strength, but this was not necessarily ensured. Consequently, these vintage CBFs are expected to exhibit unacceptable performance (e.g., collapse) in large earthquakes, and this has been supported by observations from several earthquakes in Japan. The PI will collaborate with Professor Masayoshi Nakashima of the Disaster Prevention Research Institute at Kyoto University, a leading researcher in seismic steel building design, to investigate the seismic performance of vintage CBFs in Japan and the efficacy of several retrofit schemes intended to improve performance. Numerical simulation techniques developed in an ongoing parallel study conducted by the PI on vintage CBFs in the US will be utilized and modified to characterize common Japanese construction. The research will advance the understanding of the behavior and retrofit of vintage Japanese CBFs which can be applied to their US counterparts. CBFs in the US and Japan have similar lineage, and pre-capacity-design CBFs in particular have drawn considerable concern from the engineering community due to strength, detailing, geometric, and material deficiencies. Recent subassemblage testing of existing and retrofitted US vintage CBFs by the PI and collaborators has shown that these characteristics can severely limit inelastic deformation capacity or significantly affect the sequence of component yielding and failure. Leveraging the similarities between US and Japanese CBFs, this experimental data will be used to calibrate brace and gusset-plate connection models that numerically simulate vintage-CBF components common in Japan. Researchers and engineers in Japan will help establish characteristics of study buildings and determine potential retrofit alternatives, and nonlinear response history analysis will be employed using ground motion suites representative of various hazard levels. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Japan Society for the Promotion of Science.