Monitoring an In-Service Railway Bridge with a Distributed Fiber Optic Strain Sensing System

Abstract

Distributed fiber optic strain sensing systems could potentially provide a useful tool for bridge assessment by providing insights into member forces and connection behavior as well as local cross-section changes (e.g., due to deterioration) for steel truss bridges. To investigate the use of distributed fiber optic strain sensing systems, an in-service steel truss bridge that was built in 192 had a fiber optic sensing system installed at midspan at the top and bottom chord connections. Three load scenarios were used: (a) static loading using a work train, (b) dynamic loading using a work train, and (c) dynamic loading using in-service increasing trains. The static test results indicated that the strains could be used to evaluate behavior in the members, including the presence of bending moments, and the impact of connections such as gusset plates and to locate changes in the member’s cross section. The dynamic load tests indicated that increasing train speed degrades the quality of the strain measurements. However, trends in the data can still be detected and are similar to those observed during static tests, although the detection of localized strain changes was less accurate.