Extreme wind-induced roof cladding failure: A fragility analysis for nuclear power plant structures

This study addresses the wind fragility of roof cladding systems in nuclear power plant turbine buildings, which are highly vulnerable to extreme wind events due to their lightweight construction. A comprehensive framework was developed to assess wind-induced failure probabilities by integrating experimental and analytical methods. Wind tunnel tests were conducted to measure roof pressures, while pull-through and structural tests characterized strength distributions and identify failure modes. Nonlinear finite element simulations, validated against test results, were used to model structural behavior and perform fragility analysis under various wind pressure scenarios. Findings revealed that cladding failures might occur at wind speeds as low as 31 m/s (no parapet) and 37 m/s (solid parapet), which are below the 39.5 m/s of design standard, driven by localized pressure amplification caused by building geometry and topographical influences. Mitigation strategies, such as spoiler parapets, showed potential to increasing failure wind speeds to 49.5 m/s (25 % above design criteria), enhancing system resilience. These results highlight the need to review code-based pressure coefficients for critical roof zones and consider site-specific aerodynamic effects in design. While the results focus on specific cladding systems, the framework is adaptable to other materials with available property data.