IMPACT OF MASONRY INFILLS ON THE NONLINEAR SEISMIC RESPONSE OF IRREGULAR RC BUILDINGS

Despite significant research efforts, understanding the seismic behavior of infilled reinforced concrete (RC) buildings remains challenging due to the complex interaction between infill walls and the structural frame, along with various influencing factors. Current seismic codes generally classify infill walls as non-structural elements, and standardized guidelines for their modeling and analysis are still lacking. However, completely disregarding their impact may not be conservative, as infill masonry walls can significantly influence seismic performance. Recognizing this effect, Eurocode 8 mandates an amplification of seismic action effects in certain cases of infill irregularity. This study assesses the adequacy of these design provisions by examining various in-plan layouts of infill walls that fall within the code's limits, where action effect amplification or additional countermeasures are not explicitly required. Nonlinear static and dynamic analyses were performed, accounting for masonry cracking, crushing, and the deterioration of both stiffness and strength. The findings highlight that neglecting the role of infills may not always be safe. In specific cases analyzed, torsional effects and soft-story mechanisms led to structural failure, despite Eurocode 8 not mandating action effect amplification. Moreover, the results suggest that the additional shear demand induced by masonry infills, although minimal, can still contribute to an increased vulnerability of RC buildings.