Seismic Performance of Masonry Infill Walls Retrofitted With CFRP Sheets

Abstract

Synopsis: A significant portion of existing building stock that was constructed prior to the enactment of modern seismic design provisions consists of gravity-load-designed reinforced concrete frames, infilled with unreinforced masonry walls. These structures are susceptible to extensive seismic damage when subjected to strong earthquakes and require retrofitting in order to comply with the provisions of current building codes. Experimental investigation of gravity-load-designed reinforced concrete frames, infilled with concrete block masonry, has been conducted to develop a seismic retrofit strategy that involves the use carbon fiber reinforced polymer (CFRP) sheets. Two half-scale concrete frames, infilled with masonry walls were tested with and without seismic retrofitting. The retrofit technique consisted of CFRP sheets, surface bonded on the masonry wall, while also anchored to the surrounding concrete frame by means of specially developed CFRP anchors. The frame-wall assemblies were tested under constant gravity loads and incrementally increasing lateral deformation reversals. The results indicate that infilled frames without a seismic retrofit develop extensive cracking in the walls and frame elements. The elastic rigidity reduces considerably resulting in softer structure. The failure may occur in non-ductile frame elements, especially in columns. Retrofitting with CFRP sheets controls cracking and increases lateral bracing, improving the elastic capacity of overall structural system. The retrofitted specimen tested in the current investigation showed approximately 300% increase in lateral force resistance, promoting elastic response to earthquake loads as a seismic retrofit strategy. Experimental observations and results are presented in the paper.