Health Monitoring of Prestressing Tendons in Posttensioned Concrete Bridges

Abstract

Currently 90% of bridges built in California are posttensioned box girder. In such structures, the steel tendons are the main load-carrying components. The loss of prestress, as well as the presence of defects or tendon breakage, can be catastrophic for the entire structure. No well-established method monitors prestressing tendons that can provide simultaneous information related to the presence of defects and the level of prestress in a continuous, real-time manner. If such a monitoring system were available, considerable savings would be achieved in bridge maintenance because repairs would be implemented in a timely manner without traffic disruptions. This paper presents a health-monitoring system for prestressing tendons in posttensioned structures of interest to the California Department of Transportation. Such a system uses guided ultrasonic waves and embedded sensors to measure the level of applied prestress and to detect defects at early growth stages simultaneously and in real time. The results of tests on a large-scale, single-tendon posttensioned joint specimen, subjected to multiple load cycles, are presented to validate the monitoring of prestress loads (through nonlinear ultrasonic probing) and the monitoring of damage progression and location (through acoustic emission techniques).