Cumulative effects due to seismic sequences in RC frames designed with force- and energy-based approaches

Assessing the long-term seismic performance of buildings under sequential earthquake events is a significant challenge in earthquake engineering. Recent seismic events, such as the 2023 Turkey series, consistently demonstrate that the cumulative effects of multiple seismic actions can lead to severe structural damage or collapse, even when not exceeding design-level peak ground accelerations. This highlights a critical gap in current seismic standards, which predominantly focus on a single reference earthquake for each hazard level, neglecting the cumulative impact of an earthquake sequence. The energy-based methodology offers a robust framework to address this, as it directly quantifies the cumulative energy dissipated through plastic deformations, an indicator of cumulative damage. This paper investigates the seismic response of a 6-story reinforced concrete bare frame, explicitly considering P-Δ effects, when subjected to near- and far-field earthquake sequences. The frame was designed using both force-based and energy-based approaches to evaluate their performance under these events. The response under seismic sequences is assessed at both local (story-level) and global (entire frame) scales, utilizing deformations, dissipated energy, and the Park and Ang damage index. Our findings indicate that maximum deformation is an unsuitable parameter for evaluating the evolution of damage during a seismic sequence, as it does not necessarily increase during aftershocks despite ongoing structural degradation. Dissipated energy is a much more adequate parameter since it is a cumulative magnitude.