EVALUATION OF FRAGILITY OF INFILLED FRAME STRUCTURES SUBJECT AFTERSHOCKS BY MEANS OF DOUBLE INCREMENTAL DYNAMIC ANALYSIS APPROACH

The paper investigates the role of masonry infill walls on the seismic fragility of reinforced concrete structures subject to mainshock/aftershock sequences. An assessment framework aimed at determining aftershock fragility curves of bare frames and infilled frames is presented. The framework is based on a Double Incremental Dynamic Analysis (D-IDA) approach, which provides the adoption of ground motions defined by combining a fixed intensity mainshock with a set of variable intensity aftershocks. Mainshock (MS) intensity is scaled several times and combined with the same set of aftershocks (AS). Chord-rotation and shear limit states are specifically defined to consider the influence of masonry infills within frames. The OpenSees software platform is used to carry out simulations by means of a fully fiber-section model of a reinforced concrete (RC) prototype structure. Fragility curves and residual capacity diagrams obtained show that masonry infills can provide significant additional capacity seismic to resist further shakings in comparison with bare frames, if reinforced concrete members have sufficient shear resistance