Retrofit of a soft-story woodframe building using SMA devices with full-scale hybrid test verification

Abstract

Soft-story woodframe buildings are prevalent in much of California and for decades have been recognized as a disaster preparedness problem for both the owners/tenants and community as a whole. Retrofit programs for these at-risk buildings have been proposed with the first such program in a major city mandated in San Francisco in 2013. In this paper, a seismic retrofit methodology for soft-story woodframe buildings is presented. The methodology utilizes seismic response modification devices that consist of a compact steel section for energy dissipation and shape memory alloy (SMA) wire for re-centering capability, should that be needed. The device can be installed within a scissor-jack brace which is known for its compact footprint and high displacement magnification factor. These characteristics make it suitable mainly because of the need for placement in or near short wall segments characteristic of the bottom floor of soft-story woodframe buildings. The retrofit methodology using the SMA-steel device in a scissor-jack brace was developed and exemplified on a three-story soft-story woodframe building. Nonlinear time history analysis was conducted to quantify the performance of the retrofitted building for a suite of earthquakes. Experimental validation consisted of a full-scale hybrid test of the three-story building with the seismic retrofit represented numerically in the first-story serving as the numerical substructure, and the upper two stories represented physically in the laboratory. The results of the full-scale hybrid test are presented thereby validating the proposed seismic retrofit using SMA-steel devices in scissor-jack braces.