Assessing the impact of multi-directional ground motion on RC frame buildings: a data-driven approach using vulnerability functions and regression analysis

This research explores the impact of earthquake directionality and orientation on the seismic performance of reinforced concrete (RC) frame structures, an area previously overlooked in seismic design. The multi-directional component of ground motion was not taken into consideration during the seismic performance design of the majority of RC frame structures. Focusing on a case study in Padang City, Indonesia, a region known for moderate seismic activity, this study assesses the behavior of an eight-story ordinary moment resisting frame (OMRF) under various directional components and orientation angles of ground motions. Through Nonlinear Dynamic Analysis (NL-DA) using Nonlinear Time History Analyses (NL-THA), the study incorporates 14 ground motions across East–West and North–South directions, varying from 0° to 60° in 15-degree increments. Incremental Dynamic Analysis (IDA) evaluates the building's response, employing capacity curves, fragility curves, and CMR scores to understand damage probabilities and structural behaviors under different earthquake directions. The objectives include (1) assessing the building's seismic resilience through IDA capacity curves in line with FEMA 356 performance-based design standards, (2) developing fragility curves and the CMR to predict the potential of damages and structural response in various ground motion directions, and (3) formulating a generic relationship between intensity measure (IM), structural behavior (S_B), and incidence angle (θ) via regression analysis. Results highlight the crucial role of θ in influencing structural response, with deterioration in structural behavior noted as the angle of incidence increases. This pattern underscores the varying stress distributions and deformation patterns in response to directional ground movements. The study's findings emphasize incorporating directionality in seismic risk assessments and structural designs, offering valuable insights for improving resilience against future seismic events. Eventually, the link between θ, IM, and S_B is crucial for assessing and mitigating seismic risk, since it indicates that θ is a major element impacting how buildings respond to seismic occurrences.