Evaluation of energy dissipation retrofit of soft story wood-framed buildings using fragility functions

Abstract

Natural disasters can result in large loss of life along with significant financial losses and disruptions to society. For earthquakes, modern building codes focus on design of the structural framing system to achieve a life-safety performance level for moderate to strong earthquakes and collapse-prevention for very strong earthquakes. However, there is no direct consideration of financial losses to property owners and tenants, a large portion of which is often attributed to damage of non-structural components that require repair or replacement after an earthquake. To fully understand the risks associated with earthquakes, it is necessary to assess the performance of both structural and non-structural components. The expected performance of structures during an earthquake can be evaluated by relating the intensity of the seismic hazard to the probability of a given damage state being exceeded. Such relations provide information on the overall vulnerability of structures under seismic loading and are often referred to as fragility functions. The fragility functions can be used to estimate potential losses and therefore can be used to prioritize funding for improving the resilience of seismically vulnerable communities. In this study, fragility functions were developed for a four-story wood-framed residential building with a ground story having significantly smaller lateral stiffness and strength compared to the upper stories. Such structures are known as soft-story buildings and are common in some seismically vulnerable regions of the United States. The building performance was evaluated using incremental dynamic analysis and with consideration of three distinct damage states. Two configurations are examined, one without retrofit and the other with a seismic retrofit in which energy dissipation elements are incorporated within the ground story. The effectiveness of the energy dissipation system in reducing damage is evaluated through the developed fragility functions.