Structural health monitoring of continuous prestressed concrete bridges using ambient thermal responses

Abstract

The feasibility to monitor the structural health of multi-span prestressed concrete bridges by using their ambient thermal loads and responses is investigated. An 8-m-long, 2-span continuous concrete bridge is designed and constructed to represent typical full-scale bridges. The bridge is equipped with various sensors to continuously monitor temperatures, strains, deflections, and support reaction forces, and is exposed directly to sunlight, rain, wind, and dewfall in order to attain a realistic ambient thermal loading condition. Five states of distributed flexural damage, ranging from slight to severe, are created in the experimental bridge by applying two overloaded concentrated forces. At every damage state as well as the initial undamaged state, the thermal loads and responses of the bridge are continuously monitored for several days, and these responses are compared with those predicted by a newly developed analytical model. This model takes into account of nonlinear temperature distribution in bridge cross sections, presence of prestressing forces, support flexibility, and initial crookness of bridge span. An excellent agreement between model predictions and monitored responses are obtained for the initial undamaged state. The monitored responses in five damage states are again compared with the model predictions of the undamaged state. As expected, the discrepancy between them increases with increasing of damage level. A scheme to account for distributed flexural damage is then developed for the analytical model. By using this scheme, it is possible to tune the model predictions to match with the monitored responses. Through this model tuning process, approximate damage distribution pattern and damage severity along the entire bridge length can be identified. The study clearly demonstrates that an effective structural health monitoring system based on ambient thermal loads and responses can be successfully developed for multi-span prestressed concrete bridges.