Seismic Performance of Nonductile Concrete Moment Frames Constructed to Older Building Standards

ABSTRACT Recognizing the poor performance, including the threat to safety, posed by weak, irregular, and poorly‐detailed reinforced concrete buildings, several jurisdictions in the United States have implemented or are considering implementing seismic retrofitting ordinances to improve the performance of older concrete buildings. These ordinances commonly use a benchmark year, typically 1980, to differentiate between older and modern buildings as high‐priority candidates for retrofit. However, there is a large variation in performance among nonductile concrete buildings of varying ages, and the implications of these benchmark years and their appropriateness for building performance improvement and seismic risk reduction have not been explored. This study investigates six building archetypes of concrete moment frames to assess the seismic performance of existing buildings ranging from older (1964–1994) to modern (2010–2022) designs. We consider four soil profiles of varying properties and depths, all classified as site Class D but with differing site conditions. Building performance assessments indicate that the older building archetypes do not meet ASCE/SEI 41‐23 safety evaluation criteria, confirming focus on pre‐1980 concrete buildings for retrofit. However, the results also show that large repair cost and recovery times, even for some post‐1980 buildings, may lead to demolition or residents choosing to permanently relocate because the performance may not align with societal goals. The results also show that inclusion of site‐specific response analysis that accounts for the entire soil profile above bedrock may be critical to evaluating retrofit priorities for buildings and can change the retrofit assessment outcome.