Evaluation of a strain monitoring system for existing steel railway bridges

The old steel bridges that integrate the existing railway lines are structures built with materials that are no longer used and whose knowledge has being lost over the years, often presenting severe problems of deterioration and subjected to loading environments very different from those for which they were designed. In this context, adequate strain monitoring is a crucial tool in supporting the behavior characterization and safety assessment of these structures.This article presents and discusses the monitoring systems installed in the Trezói Bridge, within a research project aimed at developing and applying procedures for evaluation of the structural integrity of steel railway bridges. The field observations of the structural behavior were accomplished by using two different types of sensors: electric and fiber optic strain sensors. The electric monitoring system was designed and installed on the bridge to supply the experimental data for the research project, while the fiber optic monitoring system was firstly applied to evaluate the reliability of the former and to check its efficiency, and secondly to provide some redundancy of the measurements at critical locations. The obtained results are analyzed to characterize the bridge behavior and the capabilities and limitations of both types of sensors to acquire the relevant data for the bridge service condition and fatigue assessment are discussed, namely in what concerns the ability to accurately capture the static and dynamic components of the structural response and the frequency content of interest.

► Two different strain monitoring systems were applied to an old steel railway bridge.
► A new procedure for the field installation of the electric strain gages was adopted.
► Traffic characterization was performed by using a simple experimental scheme.
► Both fiber optic and electric sensors were able to capture the relevant bridge response.
► Monitoring data enable to accomplish an adequate fatigue analysis of the structure.