Genetic Optimization for Seismic Retrofit of Soft-Story Woodframe Buildings Using FEMA P-807 Methodology

Abstract

Recent earthquakes around the world are reminders of the destructiveness of earthquakes and the effect they exact on lives and property. In 1989, the Loma Prieta earthquake resulted in significant damage and fatalities in the San Francisco Bay Area. Multiunit woodframe buildings suffered severe damage as a result of moderate to strong ground motions. Just 5 years later in southern California, the Northridge earthquake caused even more extensive damage to soft-story woodframe buildings. These multifamily residential buildings have upper stories with dense walls but have a large amount of openings for automobile parking at ground level, making them soft (and weak) story buildings. These buildings pose very significant safety risks to tenants, financial risks to owners, and recovery risks to all levels of government. They have been recognized as a disaster preparedness problem, and mitigation efforts are underway in San Francisco with other California cities beginning to follow. In May 2009, FEMA and the Applied Technology Council launched a project to develop a logical methodology for seismic retrofit of (soft-story) weak-story woodframe buildings in seismically active regions of the United States which resulted in the FEMA P-807 report. The objective of the study presented in this paper was to develop a method to optimize retrofit designs for soft-story woodframe buildings based on the FEMA P-807 guideline. Various constraints and objective functions were applied within a genetic algorithm to identify optimal retrofit designs within two building examples.