Seismic performance of Pakistani-technique infilled reinforced concrete frames

Infilled reinforce concrete (IRC) frames are commonly built across the world. Modern building codes address the influence of infill walls in seismic design and assessment of existing structures. Other building codes commonly consider infill walls as non-structural elements and do not require any explicit verification. One of such codes is the Pakistan Building Code (PBC), which does not foresee recommendations and guidelines for IRC frame structures, despite being a common construction typology in the Country. Records of past earthquakes show that infill types and material properties strongly affect the seismic response of buildings thus highlighting the importance of such parameters and making the topic worth investigating in detail. This paper introduces a numerical model for infill walls, which predicts different features of the nonlinear response, such as cracking, peak force, failure and residual force. Such features are expressed as function of infill friction coefficient between mortar and brick surface and mortar strength, whose effects are commonly neglected in available numerical models. The model is applied to a comprehensive case study of a three-story IRC frame factory building, located in the city of Mirpur, Pakistan, hit by an earthquake of magnitude 5.9 on 24 September 2019. The results obtained the model show good agreement with the observed in-situ damage patterns, thus revealing the importance of correctly modeling the infill walls when seismically designing and assessing Pakistani IRC buildings.