Analysis of progressive collapse of low-rise concrete frame structure under double earthquake in Türkiye

The double earthquake that struck Türkiye on February 6, 2023 killed over 50,000 people. It also caused the collapse of thousands of low-rise reinforced concrete structures in the seismic area, resulting in incredible damage. To study the reasons for the progressive collapse of numerous buildings, a nine-story concrete frame structure was established in this study, and the elastic-plastic time-history analysis under the double earthquake was performed. The element failure criterion was defined using the max equivalent compressive strain, refining the damage initiation point and transmission path of the proposed structure. The results showed that: 1. The natural period of vibration of the low-rise concrete frame structure in the seismic area is in the peak spectral acceleration region of the first earthquake, which maximizes the earthquake damage force. 2. The first strong earthquake disabled the main load-bearing columns on the ground floor of the structure, resulting in collapse within a few seconds of the second earthquake. 3. The seismic damage investigation showed that the low-rise frame structure had insufficient longitudinal reinforcement laps, insufficient transverse reinforcement and stirrups, and weak embeddedness between longitudinal bars and concrete. These issues have amplified the damage degree. 4. Despite the comprehensive building seismic regulations in Türkiye, the most pressing problem may be the long-term regulatory failure of the authorities.