Experimental Seismic Behavior of a Full-Scale Four-Story Soft-Story Wood-Frame Building with Retrofits. II: Shake Table Test Results

TLDR

Soft‑story wood‑frame buildings, largely built between the 1920s and 1960s, are a known disaster risk because their first stories lack sufficient strength and stiffness, making them prone to collapse during moderate to large earthquakes. The study aims to propose and validate retrofit methods for at‑risk soft‑story wood‑frame buildings by constructing and retrofitting a full‑scale four‑story model and subjecting it to varied ground motions. The authors performed full‑scale shake‑table tests on the retrofitted building to validate FEMA’s soft‑story seismic retrofit guideline and a performance‑based seismic retrofit methodology developed by the NEES‑Soft project. The test results confirm the effectiveness of the two retrofit approaches, providing empirical evidence for their application.

Abstract

Soft-story wood-frame buildings have been recognized as a disaster preparedness problem for decades. The majority of these buildings were constructed from the 1920s to the 1960s and are prone to collapse during moderate to large earthquakes due to a characteristic deficiency in strength and stiffness in their first story. In order to propose and validate retrofit methods for these at-risk buildings, a full-scale four-story soft-story wood-frame building was constructed, retrofitted, and subjected to ground motions of various intensities. The tests were conducted to validate retrofit guidelines proposed in a "Federal Emergency Management Agency's recent soft-story seismic retrofit guideline for wood buildings" and a performance-based seismic retrofit (PBSR) methodology developed as part of the NEES-Soft project. This paper is the second in a set of companion papers and presents the full-scale shake table test results using the two new approaches. The companion paper to this paper presents the design philosophies, design details, and numerical analysis of the retrofitted building for each of the four retrofits.