Performance-based seismic retrofit procedure with shake table validation

Recent earthquakes such as Loma Prieta and Northridge in California have highlighted the poor performance of a specific class of existing buildings known as soft-story building. This is because many older buildings were designed prior to the implementation of modern seismic design codes. Although building codes have clearly evolved, the problem is still unresolved for older buildings that are code-deficient such as soft-story wood-frame buildings. Retrofitting these types of buildings came to the forefront after the 1989 Loma Prieta, 1992 Cape Mendocino, and 1994 Northridge earthquakes. This paper presents a new performance-based seismic retrofit (PBSR) methodology for existing wood-frame buildings with an extreme soft-story and torsional irregularity at their first story, i.e. the most common case for these types of buildings in the San Francisco Bay Area. The method was validated numerically using non-linear time history analysis and then was validated experimentally by conducting full-scale shake table tests on a four-story wood-frame building at NHERI @ UC San Diego (formerly NEES @ UCSD), the largest outdoor shake table in the United States. The method is shown to be applicable to these types of buildings and some advantages of the PBSR method over soft-story only retrofit methodologies are presented.