Ground Motion Duration Effects on the Seismic Risk Assessment of Wood Light-Frame Buildings

Wood construction comprises a large portion of building stocks of several countries across the globe with high preparedness for earthquakes including Japan, Canada, and the United States. Built environments of these countries are prone to long-duration ground shakings due largely to the proximity of subduction faulting systems. However, the current seismic design requirements do not adequately emphasize this key feature of ground motions. This study evaluates the impact of long-duration ground motions on seismic risk characteristics of code-conforming wood lightframe buildings. To this end, a study matrix of wood light-frame buildings is developed incorporating with two different heights (i.e., 1-story and 4-story) and two distinct occupancies (i.e., multi-family and commercial) designed for a very high seismic region according to the latest pertinent design requirements of the United States. The seismic performance of these buildings is assessed through incremental dynamic analysis (IDA) in accordance with FEMA P-695 recommendations. Each building is analyzed using three sets of ground motions, i.e., far-field FEMA P-695 ground motions ensemble, an ensemble of short-duration ground motions, and an ensemble of long-duration ground motions. For each building, structural responses are obtained, and collapse fragility for these three sets of ground motions are derived. Next, the structural analysis results are relayed to a component-based loss assessment framework developed based on performance-based earthquake engineering principles in order to predict the seismic risk characteristics of the adopted buildings including the vulnerability function, risk curve, and average annual loss (AAL). The loss assessment is conducted separately for the structural and nonstructural components as well as the content of the buildings. The study reveals the considerable effect of ground motion duration on the seismic vulnerability of light-frame wood buildings, specifically in the case of 4-story wood light-frame building which reveals approximately a mean increase of 140.0% in the predicted losses

A Probabilistic Casualty Model to Include Injury Severity Levels in Seismic Risk Assessment

Despite the increasing adoption of Performance-Based Earthquake Engineering (PBEE) in seismic risk assessment and design of buildings, earthquakes resulted in around 1.8 million injuries (three times the number of fatalities) over the past two decades. Several existing PBEE-based methodologies use rudimentary models that may not accurately estimate earthquake-induced casualties. Even when models are suitable for predicting the total number of fatalities and critical injuries, they may fail to adequately differentiate between different levels of injury severity. This paper draws attention to the importance of extending the seismic casualty assessment method by broadening the perspective on injury severity. To this cause, a probabilistic model is developed to predict fatalities and injuries due to earthquakes. The proposed model adopts the FEMA P-58 framework for risk assessment and considers six injury severity levels (minor, moderate, serious, severe, critical and fatal), in accordance with the Abbreviated Injury Scale (AIS). The aforementioned framework evaluates the casualty risk with five modules: seismic hazard analysis, structural analysis and response evaluation (using incremental dynamic analysis), building collapse simulation, detailed casualty assessment caused by structural, nonstructural, and content components of the building, and injury severity assessment. The injury severity assessment module assumes two modes of injury: occupants falling on the floor resulting in injury and injuries caused by unstable building contents hitting occupants as a result of sliding or overturning. The framework uses an occupant-time location model to predict the number of injuries and a set of building content fragility curves for sliding and overturning failure modes, developed by the incremental dynamic analyses. The proposed model was applied to a case study of a reinforced concrete, moment-frame office building furnished with 21 different content objects. The results show that the frequency of injuries resulting in hospitalization can be up to 30 times more than that of the fatal injuries at low shaking intensity levels and may amplify by 20 times at high intensity shaking