Behavior of un-reinforced concrete masonry infill walls under lateral earthquake loads. (c2016)

Abstract

Reinforced concrete buildings with unreinforced masonry infill walls constitute the majority of new and old building inventories in the Middle East. In the absence of mandatory earthquake design requirements, such buildings may be susceptible to costly and life-threatening damage caused by high seismic activity. The location of Lebanon on the intersection of two highly active tectonic plates, serves only to exacerbate this issue; making the investigation of the behavior of such walls under seismic loading an urgent affair. This research summarizes past findings and commonly accepted theories on the behavior of such infills, and outlines limitations of existing work. Shake table experimental testing is utilized on 3:10 scaled specimens of a single story reinforced concrete frame with a masonry infill wall in between. The frame is designed and constructed with local materials and according to commonly used construction practices in the region. The specimens are instrumented and tested with simulated out-of-plane ground motion of the 1940 El Centro earthquake Displacement and strain data is recorded and compared with a computer model of the frame modeled using a finite element analysis software. Comparisons are also made between the observed overall behavior and that predicted by the computer model. While the specimens recorded strains in the mortar joints exceeding cracking limits, the overall out-of-plane stability of the wall in out of plane bending was maintained and no collapse of the infill was recorded. Findings are formulated into recommendations and conclusions are made concerning the use of such structural elements in widespread building construction.