Fragility curves for reinforced concrete frames with retrofitted masonry infills

Seismic retrofit of existing reinforced concrete framed buildings often involves both structural members and infill walls. The strengthening of infill walls is mainly aimed at preventing out-of-plane mechanisms and, in some cases, also increases in-plane capacity. On the other hand, the enhancement of the infill's strength might modify the failure mode of the frame, as stated by recent studies. In the case of gravity load-designed buildings, the presence of strong infill walls can lead to brittle failure of columns due to local interaction. This study investigates the effects of the in-plane shear retrofit of infills on the seismic behaviour of reinforced concrete buildings through non-linear dynamic analyses on a three-dimensional infilled frame. The seismic response of the structure is analysed in case of un-reinforced masonry wall and retrofitted wall, considering two types of retrofit. The analysis results are used to calibrate a simplified model aimed at computing fragility curves of reinforced concrete infilled frames and updating existing formulations, in order to account for the properties and the type of the infill. The proposed parameter can be applied in vulnerability assessment studies and for the design of new buildings.