Seismic strengthening of masonry infills in RC frame buildings using composite textile reinforced mortar

A real case study belonging to the class of reinforced concrete (RC) infilled buildings designed without anti-seismic prescriptions is examined in this paper. It is a 7-storey residential building erected in Italy in the late 1950s, with a pure RC frame structure and hollow masonry infills. A seismic performance assessment study in current state is carried out via incremental dynamic analysis (IDA), referring to the set of nine hazard levels provided for by the Italian Technical Standards. At a first step, the analyses are developed on the bare frame; then, infills are included in the structural model, simulated as equivalent non-linear strut elements. The results highlight a better performance of the frame structure in infilled configuration and a significant vulnerability both of infills and RC members. Based on these results, a retrofit strategy is proposed, consisting in the application of a thin layer of Composite Textile Reinforced Mortar on both sides of each infill panel, reinforced with a glass fiber net, which minimizes the added thickness, and thus impact and cost of the intervention. The IDA analyses are replicated on the building in retrofitted conditions, showing a significant improvement in the seismic response of the infills and, consequently, also of the RC structure.