Seismic fragility assessment of infilled frames subject to mainshock/aftershock sequences using a double incremental dynamic analysis approach

The paper presents an assessment framework aimed at evaluating seismic fragility and residual capacity of masonry inflled reinforced concrete (RC) frames subject to mainshock/aftershock sequences. A double incremental dynamic analysis (D-IDA) approach is used, based on the combination of a mainshock (MS) signal at diferent intensities with a set of spectrum-compatible aftershocks (AS) scaled in amplitude with respect to peak ground acceleration. Limit state functions, specifcally defned for inflled frames, are used to detect chord-rotation exceeding and shear collapse of RC members during standard and double incremental dynamic analyses. Intact and aftershock fragility curves are obtained for a reference full-scale RC frame specimen, by simulating seismic response with and without inflls through a fully fber section model developed in OpenSees. D-IDA results allow also defning aftershock residual capacity domains and loss diagrams, which are used to compare responses of bare and inflled frames subject to increasing MS intensities. Results show that masonry inflls can drastically reduce seismic fragility of RC frame structures during main events and AS, and also limit and economic losses for the midlow intensity earthquakes. Such benefcial contributions, however, depend on the capacity of RC members to support additional shear demand due frame-infll interaction and avoid sudden failures which conversely occur.