Biaxial Bending Response of Prestressed Concrete Girders Subjected to Accidental Asymmetric Prestressing Strand Loss

Abstract

Bridge prestressed concrete girders are vulnerable to sudden rupture of prestressing strands caused by accidental collisions with over-height trucks. These incidents often result in the asymmetric loss of prestressing strands and concrete sections, generating a biaxial bending moment caused by the combined effects of lateral bending and existing service loads. The induced lateral bending moment reduces the flexural resistance of prestressed concrete (PC) girders. However, the current AASHTO LRFD (load and resistance factor design) provisions for flexural resistance in PC members do not explicitly address the complexities introduced by biaxial bending, leaving the extent of strength reduction uncertain. This paper presents a series of 3-D nonlinear finite element (FE) models developed using LS-DYNA software. Four models were validated against full-scale experimental data. Force-deflection relationships were established, and the FE results were compared with predictions based on AASHTO LRFD provisions. This study concludes that lateral bending moments resulting from asymmetric losses of prestressing strands and concrete section reductions can reduce flexural resistance. The findings reveal that the AASHTO LRFD flexural resistance overestimates the residual flexural capacity of girders affected by biaxial bending by an average margin of 15%. To address this, an accidental lateral eccentricity reduction factor Ψ_IM of 0.85 is proposed for quickly incorporating the effects of biaxial bending in scenarios similar to those modeled in this study. The proposed factor is based on idealized FE simulations and is not intended for universal application to all impact damage cases. For real-world incidents, a case-specific assessment using refined analysis and diagnostics is recommended.