Infill Walls Effect on the Structural Performance of a RC Buildings Frame: A Study Based on Wall Modeling by Strut Element

This study investigates the seismic performance and behavior factors of reinforced concrete (RC) frames, focusing on the significant influence of masonry infill walls. While standard design codes like ACI-318, CSA-A23.3, and TBDY-2018 provide framework provisions, the structural contribution of infill walls is often neglected, leading to potential discrepancies between design assumptions and actual seismic response. The research employs a dual analytical approach, Nonlinear Static Pushover Analysis and Nonlinear Time History Analysis (NTHA), using ETABS 22 software. Four distinct structural configurations—Bare Frame (BF), Fully Infilled Frame (FIF), Partially Infilled Frame (PIF), and Soft Story Frame (SSF)—are evaluated to determine their overstrength, ductility reduction and response modification factors. The masonry infill walls are modeled using the equivalent diagonal strut method, accounting for their non-isotropic and brittle nature through parabolic stress–strain relationships. A core component of the study is the assessment of structural damage through a time-dependent Damage Index (DI), calculated by correlating displacement demands from NTHA with yield and ultimate displacements derived from idealized bilinear capacity curves. The findings highlight how the configuration of infill walls—specifically vertical and plan irregularities—modifies lateral stiffness, natural periods, and failure modes. The study concludes that accounting for the interaction between the RC frame and infill walls is critical for accurate seismic assessment, as these elements can transition failure mechanisms from ductile to brittle modes.