Evaluation of flexural cracks in a concrete girder railway bridge using displacement influence lines

Abstract

This paper introduces a methodology for detecting flexural cracks in concrete railway bridges based on the displacement influence line (DIL) and a probabilistic damage index formulated using a Bayesian method. Bridge displacement responses were collected under moving train loads and used to derive the most probable DIL, along with associated uncertainties, without requiring prior structural models. A damage indicator was defined based on variations in the DIL coefficients, and damage probability is quantified using Gaussian approximations. The methodology was validated using a finite element model (FE-model) of an existing concrete railway bridge, incorporating rail-structure interactions. To assess the impact of flexural cracks on the overall bridge response, three types of flexural cracks at different locations with varying depths and three measurement locations were considered. The results demonstrated that the DIL-based approach is more sensitive to local flexural cracks than traditional modal parameters. Furthermore, the method allows for potential damage detection using displacement data from a single sensor, unlike modal parameters which necessitate an array of sensors. The proposed framework offers a probabilistic interpretation of damage, enabling infrastructure managers to assess the severity and prioritize inspections. Recommendations for sensor deployment and practical considerations for field applications are discussed to support implementation in real-world bridge monitoring.