Sustainability and Resiliency Comparison of Soft-Story Wood-Frame Building Retrofits

Abstract

Soft-story wood-frame buildings have been identified as a major issue of disaster preparedness. Both the City of San Francisco and the City of Los Angeles have mandated retrofit of these building types. Thus an abundance of research is being conducted on soft-story retrofits. Two popular design approaches being investigated include the FEMA P-807 guidelines and various performance based seismic design methodologies. Despite the large amount of effort being invested in understanding the behavior of soft-story buildings, the anticipated losses if these buildings go un-retrofitted, the improved performance achieved via retrofit, and the optimal way to retrofit the large quantity of soft-story wood-frame buildings (on the order of 14,000 buildings) in a timely and cost-efficient manner, no such research is being conducted on the sustainability of the various retrofit options. Resilience and sustainability are both important research themes, and thus both need to be investigated. This paper performs a sustainability and cost analysis on several soft-story wood-frame building retrofits found in the research literature that have been previously tested for their seismic performance. These include two retrofit designs following the FEMA P-807 guidelines, with cross-laminated timber (CLT) rocking walls and special steel moment frames (SMF). Additionally, a performance-based seismic retrofit is analyzed which uses special steel moment frames on the soft-story and wood shear walls on the upper stories. The sustainability analysis measures the weighted resource use (e.g., iron ore, wood fiber), the CO2 emissions and the primary energy consumption from the life cycle of each retrofit being considered. The raw material cost and sustainability analysis are performed for the life cycle of the raw materials making up the soft-story retrofits. The life cycle includes the product phase (manufacturing and construction), construction phase (construction installation process and transport) a 50-year use phase (operation), and the end-use phase (demolition, and disposal including recycling and landfill). Recommendations are made based on cost, sustainability, and resilience tradeoffs for better informed decision making.