Effect of Unreinforced Masonry Infill Walls on Seismic Performance of Reinforced Concrete Framed Structures

Unreinforced Masonry infill walls (URM) are commonly used in the Reinforced Concrete (RC) framed structures as interiors and exteriors partition walls. Although they usually are not considered in the structural analysis and design, their influence on the seismic performance of the framed structures is significant. A common practice in the modern and old RC buildings is to remove the URM walls in the lower stories for commercial reasons; garages, storages, shops etc.

In the present work, the effect of the URM walls on seismic performance of the RC framed structure will be studied. For that, three groups of 2-D three-bay framed structures, which are fully and partially infilled with the URM walls, will be studied. These groups are classified as three stories, six stories, and nine stories RC framed structures representing low, medium and, high rise buildings; respectively. In each group, different infill panels' configuration will be studied in order to simulate the cases of ignoring or considering the stiffness and strength of the URM. Double-strut nonlinear cyclic model for masonry panels has been utilized in order to account for the structural action of the URM walls. Pushover analysis is adopted for the evaluation of the seismic response of the frames considering the material inelasticity and the geometric nonlinearity in the analysis.

Some selected numerical simulation results in terms of base shear forces, lateral deflections, and inter-story drift ratios are obtained for all the considered configurations and presented in comparative way. The regular distribution of the infill walls can improve the framed structure performance. However, omitting the infill from the ground story leads to soft story phenomena as the columns in this story are more vulnerable due to the shear forces acting on them.