4-Story Full-Scale Soft-Story Woodframe Building Test at UCSD

A full-scale four-story building was constructed and tested at the outdoor shake table facility at NEES at UC San Diego Large High Performance Outdoor Shake Table (LHPOST). The building represented a corner building with two adjacent building on the North and West sides. The test building had four garage doors at the first floor on its south side and two windows, a storage and an entrance door on its east side. The upper stories had two two-bedroom units with bay-windows on the south and east sides, respectively. Four different retrofit designs were developed for the four-story woodframe building. The retrofits were designed based on FEMA P-807 retrofit guideline and performance-based seismic retrofit (PBSR) concept. The building was retrofitted and tested in four different phases where the first two phases were conducted to verify the FEMA-P807 retrofit guideline and the last two phases were conducted to verify the effectiveness of the PBSR retrofit procedure. Cross laminated timber (CLT), steel special moment frames (SMF), and viscous dampers combined with wood structural panels (WSP) were used as retrofit techniques in these tests. In the P807 retrofit procedure, the goal is to achieve an acceptable performance by limiting the retrofit to the bottom story (i.e., soft story) to reduce the cost and time of retrofit. Whereas, in the PBSR methodology, the retrofits are not limited to the bottom story and can be applied to upper stories to increase the strength of the building which leads to better overall performance. The building was subjected to the similar ground motions that were recorded after the Loma Prieta, 1989 and Cape Mendocino-Rio, 1992 earthquakes. The earthquakes were scaled to DBE and MCE levels with maximum spectral accelerations of 1.2g and 1.8g, respectively. Before and after each seismic test, white noise tests with root mean square (RMS) of 0.05g were conducted to get the fundamental period of the building and its mode shapes. In the last phase of testing, the building was tested to collapse. Below is a brief description of the testing phases: Phase 1 (P807 – CLT) The building was retrofitted with cross-laminated timber (CLT) panels at its first story. The building was subjected to ground motions with spectral acceleration of 0.2g and 0.9g. A total number of four seismic tests were conducted. Phase 2 (P807 – SSMF) The building was retrofitted with steel special moment frames (SMF) at its first story. The building was subjected to ground motions with spectral acceleration of 0.24g and 1.1g. A total number of four seismic tests were conducted. Phase 3 (PBSR – SSMF) The building was retrofitted with steel special moment frames (SMF) and wood structural panel (WSP) at its first story and wood structural panel and Anchor Tie-Down System (ATS) rods at the upper stories. The building was subjected to ground motions with spectral acceleration of 0.2g, 1.2g and 1.8g. A total number of five seismic tests were conducted. Phase 4 (PBSR – FVD) The building was retrofitted with fluid viscous damper (FVD) at its first story and wood structural panel and Anchor Tie-Down System (ATS) rods at the upper stories. The building was subjected to ground motions with spectral acceleration of 0.5g, 1.2g and 1.8g. A total number of five seismic tests were conducted. Phase 5 (Collapse) The retrofits were removed and the building was subjected to ground motions with spectral acceleration ranging from 0.4g to 1.8g. The building collapsed when subjected to Superstition Hills ground motion scaled to spectral acceleration of 1.8g for the second time. A total number of eight seismic tests were conducted.