Advanced post-earthquake safety assessment: a novel probabilistic approach for quantifying dissipated energy using aftershock vibration response

Following a severe earthquake, prompt assessment of remaining buildings is essential for safe occupancy. Current methods involve field inspections by experts in which the buildings are categorised using red, yellow or green placards. Red-tagged buildings must be avoided due to the risk of collapsing in aftershocks, while green structures are deemed safe. However, yellow-tagged buildings present uncertainty, necessitating more detailed evaluation. This study introduces a novel method, 'seismic assessment based on aftershocks' (SABA), evaluating the safety of yellow-tagged structures by analyzing their vibration responses under aftershocks. This innovative approach provides valuable insights, especially in cases lacking measurements under the mainshock. SABA utilises the unscented Kalman filter (UKF) to estimate dissipated energy and probabilistically calculates maximum drift (MD) during the mainshock using incremental dynamic analysis (IDA) or Bayesian theory. Validation involved a nonlinear SDOF Bouc-Wen model estimating MD for 14 earthquakes, demonstrating robustness with an average IDA-based method error of 14% and Bayesian method error of 15%. Further validation estimated MD in a full-scale experimental RC column under an aftershock, revealing less than a 10% disparity between estimates and actual values. Despite inherent risks, aftershocks emerge as pivotal factors in assessing the safety of building clusters, as highlighted by these findings.