Health monitoring of joint conditions in steel truss bridges with relative displacement sensors

• A relative displacement sensor is used to perform the health monitoring of joints.
• Joint connection conditions in gusset plate of steel truss bridges are assessed.
• Experimental studies on a steel truss bridge model are conducted.
• The sensitivity and performance of the sensor in joint monitoring are investigated.
• Measured relative displacements under ambient and free vibrations are used.

This paper investigates the feasibility and effectiveness of using a recently developed relative displacement sensor for the structural health monitoring of joint conditions in steel truss bridges. The developed relative displacement sensor is an innovative design offering some advantages and unique features, and is a much easier and economical method for structural health monitoring due to the simplicity of its direct measurement of relative displacement without the requirement for a stable reference point. To investigate the performance of applying the developed relative displacement sensors for structural joint condition monitoring, a steel truss bridge model is fabricated in the laboratory and installed with the relative displacement sensors to detect the health conditions of joint connections. The dynamic relative displacement measurements are analyzed with a time-frequency analysis method, i.e. continuous wavelet transform, which is a well-practiced signal processing technique to identify the structural condition change, namely the loosen bolt damage in the joint connection of steel truss bridges under ambient vibrations. The sensitivity range of the developed sensor is also investigated to see how sensitive the sensor is to identify the local bolt damage. Relative displacement measurements of the steel truss bridge models under free vibration tests from both undamaged and damaged states are also analyzed, and a damage index based on the change in the percentages of a specific wavelet packet component to the total wavelet packet energy between the undamaged and damaged states is used to detect the existence of the loosen bolt damage in steel truss bridges. Experimental studies demonstrate that the developed relative displacement sensor has a sensitive performance to identify and assess the joint conditions in steel truss bridges.