Response and fragility assessment of bridge columns subjected to barge-bridge collision and scour

Abstract This paper studies barge impact performance of bridge columns. The effect of various design parameters and the free length of pile, which could be either by design or caused by scour, are studied. Additionally, a preliminary analysis is conducted to assess the post-collision safety of bridges to carry traffic loads. In order to aid design and management of bridges with a wide range of design and geometric parameters, metamodels are developed to estimate the force demands and fragility for bridges columns subjected to barge impact. In order to derive these probabilistic models, finite element simulations are performed for 2000 bridges with varying combinations of design characteristics, barge properties, and impact velocities. In each simulation, a non-linear dynamic analysis is performed to evaluate the maximum shear force, moment, shear strain, and curvature in the columns. Following the dynamic analysis, vertical load analysis is conducted to determine the post-collision stability of bridges under vehicular loads. These analyses are repeated for all the bridge samples for various values of free pile lengths (possibly due to pier scour) to understand its effect on the barge impact performance of bridges. The results highlight that depending on the pier properties and impact conditions, the failure may be caused due to shear, flexure, or a combination of both; however, presence of free pile length leads to more flexure dominated failures. Beyond the insights gained from these response analyses, this paper develops parameterized polynomial response surface models, which can be used to predict the shear and flexural response for a wide range of bridge characteristics and collision conditions without the need for any additional finite element simulations. Finite element simulation results are further employed to derive fragility models using logistic regression. These fragilities can be applied to a wide range of bridges and collision conditions to evaluate the probabilities of exceeding the ultimate shear strain and column curvature capacity limits when a bridge pier is subjected to barge impact. The metamodels developed in this study are applied to a case study bridge to show the variation in demands and fragility as the bridge parameters, free pile length (scour depth), and collision conditions are varied.