Modification Factor and Ultimate Strength of Infilled Frames, Rehabilitated by Concrete Covers

Most rehabilitation codes have a special part for regular masonry infill panels. However, they are completely silent for infills improved by concrete covers, probably for the lack of sufficient experimental test data. Shotcreting one side or both sides of the existing infills is one of the best methods to improve structural seismic behavior. Therefore, this paper focuses on the ultimate strengths and modification factors of this type of infill panels, based on the existing experimental data of the literature. The existing formula of the codes is improved to estimate ultimate strength of such infill panels. Furthermore, modification factors of primary and rehabilitated specimens are calculated and compared. In this regard, envelopes of the load–displacement behavior of the specimens are applied, as well. It is shown that envelops give more conservative values for the m-factor, compared with the standard backbone curves. It is shown that modification factor of masonry infill panels is decreased when rehabilitated by concrete covers; however, for clay tile infills, it remains almost unchanged.