Impact of composite columns on soft and weak storey irregularities in buildings without ground floor infill walls

In buildings without infill walls on the ground floor, structural irregularities, such as soft and weak storey irregularities can significantly reduce their resilience to earthquakes. These irregularities arise from insufficient lateral stiffness and strength in the ground floor structure, leading to instability during seismic events. This study investigated the seismic performance of frame structures, focusing on two key factors: the lateral rigidity provided by infill walls and the potential benefits of replacing conventional columns with composite columns on the ground floor. The analysis was conducted in accordance with the Turkish Building Earthquake Code 2018 (TBEC-2018), which provides specific guidelines for designing structures to withstand seismic forces. The findings revealed that including the lateral rigidity of infill walls in the analysis increased the cracked cross-section’s moment of inertia by 5%. While this addition enhanced the building’s lateral load resistance, it also increased the rigidity irregularity coefficient by 33%, indicating a potential redistribution of seismic forces that could affect the overall stability. On the other hand, introducing composite columns on the ground floor helped reduce the rigidity irregularity coefficient by 20%, providing a more uniform response to lateral loads. However, this improvement came at the cost of a 29% increase in the strength irregularity coefficient, highlighting the challenges in balancing stiffness and strength irregularities. These findings emphasize the importance of carefully evaluating structural modifications to optimize seismic performance. While composite columns are effective in mitigating rigidity irregularities, their impact on strength irregularities must be managed to avoid compromising overall safety.