Evaluation of severe reinforced concrete building collapses in the context of structural–soil characteristics during the February 6, 2023 Kahramanmaraş earthquakes

The February 6, 2023 Kahramanmaraş Earthquake doublet represents an unusual case in global earthquake history, with two major events of M w > 7.0 occurring on the same day in nearby regions. These earthquakes caused extensive destruction across 11 provinces of Turkey, particularly severe collapses in reinforced concrete buildings. In this study, 119 collapsed reinforced concrete buildings located in the most heavily damaged areas of Kahramanmaraş city center were examined in terms of their structural, architectural, and geometric characteristics. All buildings included in the investigated inventory collapsed during the Pazarcık M w 7.7 event, before the occurrence of the Elbistan M w 7.6 earthquake. In addition, the spectral characteristics of the earthquakes were analyzed, and three-dimensional finite element (FEM) models were developed to determine their dynamic properties. The interaction of the collapsed buildings with other structures within the same parcels was evaluated. Furthermore, the historical evolution of seismic codes and the design principles of the buildings were analyzed. In addition, the available regional and project-based geotechnical information was evaluated to assess the potential contribution of local ground conditions and foundation–structure response to the observed damage mechanisms. The results highlight that the widespread destruction resulted from the combined effects of structural deficiencies, local ground conditions, and soil–structure interaction. In particular, the performance of existing buildings on weak soil conditions was found to be highly inadequate. Additional contributing factors include deficiencies in urban planning, non-compliance with earthquake engineering principles in architectural and structural system design, poor construction practices, and user interventions that altered the load-bearing systems over time, thereby increasing collapse risk. Although spectral demands at some stations approached or exceeded the code-based design spectra over certain period ranges, the observed collapses cannot be explained by spectral demand alone and should be interpreted within the combined framework of structural vulnerability, local ground conditions, and foundation–structure response. Moreover, soil investigation reports were unavailable for a substantial proportion of the collapsed-building inventory, indicating considerable uncertainty in site characterization and geotechnical design documentation. This documentation deficiency should not be interpreted as direct evidence of soil-induced collapse. These findings suggest that adverse local ground conditions and soil–structure interaction may have acted as compounding factors, particularly in buildings already characterized by substantial structural and material deficiencies. In this context, recommendations are provided to enhance structural robustness and safety in future seismic codes, with emphasis on the appropriate consideration of local ground conditions and soil–structure interaction in seismic assessment and design.