Evaluation of Flexural Capacity of Prestressed Composite Girders with Corrugated Steel Webs at Elevated Temperatures

Abstract Prestressed composite girders with corrugated steel webs (PCGCSWs), widely adopted in bridge engineering, are particularly vulnerable to fire-induced damage due to the combined effects of mechanical properties degradation in the temperature-sensitive steel web and prestressed bars, coupled with the decrease in the degree of shear connection at elevated temperatures. However, research on the fire-induced flexural capacity of PCGCSWs remains insufficient, rarely incorporating the coupled effects of interface slip and prestress increment, and reliable theoretical prediction models are still lacking. This study aims to fill this research gap by establishing a comprehensive analytical framework and a nonlinear finite-element (FE) numerical method to accurately evaluate the flexural behavior of PCGCSWs under fire conditions. Based on the quasi-plane section assumption and plastic theory, theoretical formulas are proposed for the first time to predict the elastic and ultimate flexural capacities of PCGCSWs at elevated temperatures, incorporating the effects of steel–concrete interface slip and the prestress increment in prestressing bars. The validity of the proposed formulations is verified through fire tests and FE parametric analyses. The results indicated that the flexural capacity of the girder deteriorates significantly with increasing temperature, resulting in an overall reduction of approximately 80% from ambient conditions to 800°C. The interface slip effect intensifies at elevated temperatures due to the degradation of stud stiffness, though its influence diminishes beyond 600°C as material softening becomes dominant. Furthermore, elevated temperatures cause severe deterioration in the mechanical properties of prestressing bars, leading to a substantial reduction in the effective prestressing force. At 800°C, the near-complete loss of prestressing effect, coupled with a pronounced increase in girder deflection, renders the structural response comparable to that of a conventional non-prestressed composite girder. This study provides an analytical approach and numerical procedure for assessing the flexural behavior of PCGCSWs under fire, offering guidance for their design and safety evaluation at elevated temperatures.