Measuring Thermal Response of Bridges Using Vision-Based Technologies and LVDTs

A robust structural health monitoring approach measuring the structural responses of bridges such as displacements, strains etc. helps to ensure their safety and serviceability. Static and dynamic loads from vehicles and pedestrians influence the instantaneous responses of bridges, while thermal loads from daily and seasonal temperature variations influence bridge long-term responses. Vision-based monitoring (VBM) is an emerging non-contact, non-destructive monitoring approach. It utilizes cameras to capture sequential images of the structure under load and suitable image processing algorithms for target tracking. VBM has shown promising accuracy in static and dynamic response measurements of bridges, however, the evidence of its accuracy in thermal response measurements is limited. This research illustrates the results of laboratory experiments implementing VBM for thermal response measurements. Thermal responses of a laboratory truss are monitored with VBM and contact sensors such as thermocouples and linear variable differential transformers (LVDT). Cyclic temperature loads are applied to the truss to simulate daily temperature variations. The truss is monitored with GoPro cameras and contact sensors. Measured response trends by VBM and LVDT are comparable, indicating the accuracy of VBM to measure thermal responses. Thermal responses measured by VBM are higher than those of LVDT, signifying requirement for measurement resolution enhancement. The measurement resolution of VBM is 0.099 mm/°C and LVDT1 is 0.041 mm/°C respectively. This discrepancy can be attributed to non-identical targets of VBM and LVDT, resolution of the camera, efficiency of the feature tracking algorithm and robustness of LVDT output. This case study illustrates the feasibility and challenges of VBM for thermal response measurement.