Experimental and analytical seismic evaluation of concrete masonry-infilled steel frames retrofitted using GFRP laminates

The study conducted herein focuses on investigating the retrofitting effect of face shell mortar bedding (FSMB) hollow concrete masonry-infilled steel frames (CMISF) subjected to in-plane lateral loads using glass fiber reinforced plastic (GFRP) laminates that are epoxy-bonded to the exterior faces of the infill walls. The study involves three main phases, the first phase studies the in-plane behavior of unreinforced masonry (URM) wall subassemblages strengthened with different GFRP composite laminates. A total of fifty-seven URM assemblages were tested under different loading conditions. Parameters such as the type of fibers, the number of plies, and the fibers orientation were investigated. Results showed that the application of GFRP laminates on URM has a great influence on strength, post peak behavior, as well as failure modes. An increase of 90% for compressive strength was achieved using the GFRP laminates and the shear strength increased by fourteen fold.; The second phase focuses on enhancing the in-plane seismic behavior of URM infill walls when subjected to displacement controlled cyclic loading. Six full-scale single story single bay steel frames with different wall configurations were tested. The retrofitting technique using GFRP laminates aims at creating an engineered infill wall with a well defined failure mode and a stable post peak behavior as well as containing the hazardous URM damage and preventing catastrophic failure. Results showed that the GFRP prevented both shear and tension cracking by supplying the required tensile strength. The GFRP also increased the lateral load capacity and enhanced the post peak behavior by means of stabilizing the masonry face shell and preventing its out-of-plane spalling. The stabilizing allows the wall to carry more loads and prevents sudden drop in the load carrying capacity.; The third phase of the study presents an analytical model proposed for the analysis of the unretrofitted and GFRP-retrofitted masonry infilled frames. In this method, each masonry wall was replaced with a nonlinear, compression-only, diagonal strut that estimates the stiffness and the lateral load capacity of CMISF failing in corner crushing (CC) mode. The diagonal strut force-deformation characteristics were based on the orthotropic behavior of the masonry wall. A proposed method for designing the GFRP retrofitted walls in order to prevent various failure modes is also presented.