Evaluation of fatigue damage in steel girder bridges using displacement influence lines

Abstract

This paper presents a systematic method for the evaluation of fatigue damage in an existing girder bridge, utilizing the response induced by a moving vehicle. At first, a detailed and accurate finite element model was developed through a two-steps validation process using extracted modal parameters from measured accelerations and bridge displacement responses due to a moving vehicle with known axle weights. Considering real damage scenarios, three commonly found fatigue damages at the welded connections of the gusset plates, soleplates and the crossbeams were numerically simulated including their initiations and subsequent propagations. The effects of these fatigue damage were evaluated through a dynamic analysis and measuring the bridge displacement responses to a moving vehicle thus, portraying the actual in-situ measurement conditions. The static displacement influence lines (DILs) obtained from the measured signals were used as a potential damage indicator against these fatigue damages. A minimal change was observed in DILs due to incipient fatigue cracks; however, significant changes were observed when they propagated substantially, leading to fracture of the main members. For the localization of fatigue cracks, a damage index was defined by estimating the changes in DILs. Finally, the accuracy of the proposed damage detection scheme was checked with respect to the number of sensors and their locations. © 2023 Institution of Structural Engineers