Health monitoring of steel box girder bridges using non-contact sensors

Abstract

This study investigates the behavior of simple and continuous span steel box girder bridges after various damage scenarios, including bracing failure and girder fracture, and develops a non-contact bridge health monitoring technique based on the bridge dynamic responses. A series of field tests were conducted to study the feasibility of using non-contact sensors to capture the bridge dynamic responses. Moreover, detailed finite element models of the bridges were developed and validated using the field test and available experimental test results and were used to investigate the bridge failure mechanisms, maximum load-carrying capacity, alternative load paths, and dynamic responses. The bridge dynamic analysis after damage showed that bridge frequencies are sufficiently sensitive for identifying partial or full-depth girder fracture in the simple span bridges. However, these significant damages may cause very small changes in the natural frequencies of continuous span bridges. The results show a significant change in the mode shapes after damage in both simple and continuous span bridges. The mode shapes are sensitive enough to detect damage at the inflicted locations, in most cases with better resolution when compared to the frequency changes. The comparison of the intact and damaged bridge mode shapes indicates that damage at different locations along the bridge has different amplitude changes in the mode shape that could be used to localize the damage. Moreover, the analyses show that either the individual modal sensitivities or combined sensitivities are indicative for most locations throughout the span. The results also indicate a clear pattern of changes in the frequency and mode shape for each damage scenario that can be used to detect the damage type, severity, and location along the bridge.