Unraveling a Structural Failure: The Collapse of a Tunnel-Form Building in the 2023 Kahramanmaraş, Türkiye Earthquake

The catastrophic collapse of a reinforced concrete tunnel-form building (TFB) during the devastating M w 7.8 Kahramanmaraş earthquake on February 6, 2023, raises critical concerns about the seismic resilience of these widely used structures in many seismically prone countries including Türkiye. Despite their reputation for rapid construction, structural integrity and stiffness, TDBs exhibit specific vulnerabilities under extreme seismic loading, which are fundamentally governed by structural layout choices. Through a comprehensive structural assessment, this research outlines the aftermath of Kahramanmaraş earthquake sequence, analyzes the seismic data and presents a forensic engineering evaluation of a 16-story collapsed TFB located 3.2 km from the nearest free-field strong ground motion station (#4621). Utilizing a 3D fiber-based nonlinear analytical model of the structure, both linear elastic and nonlinear time-history analyses were conducted. To evaluate the adequacy of the original design under linear elastic demands, the impacts of rigid and semi-rigid floor diaphragm modeling assumptions were contrasted across both nominal design and in-situ concrete strength scenarios. Further evaluation against the Turkish Building Seismic Code reveals significant structural deficiencies and compliance gaps. Results reveal a pronounced structural discrepancy induced by severe lateral stiffness asymmetry: independent of the concrete quality, the weak direction exhibits a 1.21-fold amplification in interstory drifts under rigid and semi-rigid diaphragm assumptions at the ground floor; many shear walls exhibit brittle behavior, with failure rates reaching up to 50% in the linear analysis and 19% in the nonlinear dynamic analysis; and slabs with concentrated openings experience extreme tensile stress fields. All of these phenomena, compounded by substandard workmanship in reinforcement detailing and severely deficient concrete compressive strength, collectively triggered the catastrophic collapse of the TFB. This study underscores the urgent need for improved design methodologies, enhanced seismic detailing, and retrofitting strategies to bolster the resilience of tunnel-form buildings in earthquake-prone regions. The findings provide crucial insights for engineers, policymakers, and researchers striving to prevent similar failures in future seismic events.