Evaluation of truss bridges using distributed strain measurements

Abstract

In 2013, one in every nine steel bridges in North America was deemed to be in need of repair, retrofit or replacement. There are an estimated 200,000 steel bridges in the US alone, and an estimated $76 billion is required to return all bridges back to adequate service levels. As a result, monitoring is crucial to ensure the longevity of these structures and to avoid unnecessary replacement. To evaluate the use of distributed fiber optic strain sensors to monitor truss bridges, laboratory tests were undertaken. A scale model of the Mile 17.7 CN Rail Bridge in Jordan, Ontario, Canada was constructed and instrumented with fiber optic strain sensors prior to testing. The experimental program consisted of three point loading under three different connection conditions: i) all bolts were present and torqued, ii) one of two bolts in the connection was removed, and iii) the remaining bolts were loosened. The distributed strain measurements were used to calculate both the axial and bending strains along the full length of each member, along with the variation in truss behavior as a result of the change in connection conditions. The results indicate that the connection conditions at the truss joints can alter the behavior of the bridge.