Effect of infill walls on frames due to seismic loading

Abstract

In thc building construction, framcd structurcs are frcquently used due to ease of construction and rapid progrcss of work. Column and girder framing of reinforced concrete structurcs is in-fillcd by masonry infill pancls, solid or hollow blocks or concrete blocks. Masonry infill panels havc bccn widely used as interior and exterior partition walls for aesthetic rcasons and functional nccds. Usually in analysis only the bare frame is modeled ignoring the cffect of infills with the assumption that such modeling is rather conservativc and computationally more cfficicnt. However such assumption may lead to substantial inaccuracy in prcdicting the latcral stiffness, strength and ductility !Jf a structure. When an infillcd framc is subjccted to lateral loading, the' infills behave effcctively as struts along its compression diagonals to brace thc frames. When infill walls arc omittcd in a particular storcy, a weak storey is formed compared to much stiffer other storeys. The ground floor is the most common location, which is usually devoid of infill component due to parking or largc commercial spaces, thus resulting in a point of weakness in the structure. Normally in structural analysis it is considered that the Equivalent Static Force Method is more conservative than more rigorous dynamic procedure for regular structures or structures of smaller height. Thc present study compares the results of Equivalent Static Analysis and the Response Spectrum Analysis of frames modelcd with infills. In this investigation the performancc of masonry infill componcnts on frames under different conditions have been studicd. The masonry infill has been modeled by equivalent struts. The size, shape and other propertics of thc equivalent struts have been calculated using different published litcrature. Thc drift and flexural behavior of the frame with different combinations of infill walls have been studied and compared using both the Equivalent Static Analysis and Response Spectrum Analysis techniques. A parametric investigation has also been performed varying various parameters of the frames to observe their influences in drift and flexural behaviour of the frames. The present study is aimed at finding out the effect of infills on structures due to horizontal loading, which would lead to safe, economic and durable framed structures against earthquakes. It is observed that the Equivalent Static Analysis shows higher values for deflection and moment than the Response Spectrum Analysis only for the bare frame. Presence of infill in the frame, however, shows converse results for 6, 9 and 12 storied frames. For 4 storied frames, Response Spectrum Analysis gives higher values for both deflection and moments for the structures with or without infill components than the Equivalent Static Analysis. It is observed that moment increased depending on the increase of the infill percentage. When all bays have infill it shows the highest variation of maximum moment and conservative results are shown by the Response Spectrum analysis than the Equivalent Static one.