Seismic performance of reinforced concrete framed buildings with ribbed slabs at the affected region by 2023 Kahramanmaraş earthquakes

This study investigates the seismic performance of reinforced concrete (RC) framed buildings with ribbed slab floors in the aftermath of the 06 February 2023 Kahramanmaraş earthquakes. The structural analysis of a 6-story RC building with ribbed slab floors that collapsed during the earthquake was conducted using the finite element analysis and compared with a similar structure built with traditional slab floors. For this purpose, a sample building was selected in the Islahiye district of Gaziantep province, one of the regions most affected by the earthquake. The analysis revealed that the vibration periods of ribbed slab systems were longer than those of conventional slab systems due to their lower in-plane stiffness. Additionally, the study found that ribbed slab orientation significantly amplifies P-delta effects caused by geometric non-linearity, especially in soft-story buildings. A key finding of the study is that the high vertical accelerations recorded during the earthquakes, comparable to horizontal accelerations, generated large inertial forces that were directly transferred to the columns in buildings with ribbed slabs. These forces doubled the second-order effects in the first story compared to traditional beam-slab systems, triggering soft-story collapse mechanisms. The study underscores the high seismic vulnerability of ribbed slab buildings, particularly those without shear walls, and emphasizes the urgent need for stricter seismic design regulations to prevent future catastrophic failures.