Equivalent Load Model for Bridge Scour Effects: Experimental Validation and Design Implementation

Owing to the frequent occurrence of worldwide hydraulic hazards, scour has become a major cause of failure for cross-water bridges. Currently, the effect of scouring on bridges is not considered as an external loading, limiting its integration with other hazard loadings in reliability-based design procedures. In order to design bridges while considering the scour effect along with external and other loadings of hazardous events, developing a load model to represent the change of structural characteristics under different scour conditions is required. This paper introduces an innovative methodology that conceptually transforms the reduction of the capacity of a bridge due to the effects of scouring into an equivalent scour load, which can be used as a demand load for structural design. A series of lateral loading tests of scaled pile specimens were conducted to revise and validate the equivalent scour load formula. The proposed formula establishes a load model that considers the lateral failure mode and provides a framework for calculating failure probability by applying conditional failure probability and introducing an acceptable failure condition factor. The methodology enables direct implementation in structural analysis frameworks and the construction of scour fragility curves related to specific failure conditions, offering a systematic approach for integrating scour effects into reliability-based bridge design. The experimental validation demonstrates good agreement between the theoretical model and observed behavior, particularly for scour depth ratios less than 0.3, with limitations at higher ratios attributed to nonlinear soil stiffness effects. This approach provides engineers with a practical tool for multi-hazard bridge design while maintaining compatibility with current design codes.