In-plane behaviour of a three-storey masonry infilled RC frame

Past research and practice has shown that masonry infilling of non-seismically designed reinforced concrete frames is a decisive parameter for their seismic response and more so during the early stages of deformation. It seems, therefore, that there would be much to gain if strength and deformation capacity of masonry infilling could be enhanced, modifying its character towards that of a structural element than the current non-structural one. To that end, a research effort, part of which is reported in this paper, was undertaken investigating the possibility of converting masonry infilling to a reliable structural element employing innovative composite materials. A three-storey, RC plane frame - representing a scaled portion of a prototype existing structure - was constructed and infilled with masonry to serve as control specimen. The structure, tested under cyclic lateral loading up to failure, showed a stable response at the early stages of loading, with early cracking in masonry which accelerated during the subsequent loading cycles up to the initiation of shear cracking at the top end of one of the ground floor columns. Test results support the possibility of developing an alternative route for strengthening masonry-infilled frames: that of turning the infill to an actual structural element. This may be accomplished through the enhancement of strength and deformation capacity of the infills via suitably anchored, externally-bonded reinforcement and the provision of appropriate measures to guarantee relative monolithicity at frame-infill interface, provided that steps to exclude damage in the surrounding frame members (mainly the columns) are taken in advance.