Vibration Characteristics of an Overpass Bridge During Full-Scale Destructive Testing

Progressive destructive testing is a schematic way of applying damage on a structure and evaluating the immediate effects in terms of the change in structural characteristics. Generally a progressive destructive test is conducted on a small scale specimen in a controlled environment such as laboratory. On-site full-scale progressive damage of an existing structure, which is rare considering cost and size of the structure, is an important learning opportunity in a framework of structural health monitoring research. Such a test provides an opportunity to observe the real change in structural characteristics which often masked by environment effects. Moreover such a test can be utilized as a benchmark for several damage detection methods. In this paper a full-scale progressive destructive test of an overpass post-tensioned bridge is presented. The bridge was instrumented with vibration sensors and the ambient acceleration responses were recorded during damage stages. Damage was introduced by cutting one of bridge piers at the footing level. This type of damage is expected to simulate a condition where a bridge suffers from a non-uniform pier settlement. By applying time and frequency domain vibration analysis, as well as system identification, evolution of dynamic characteristics caused by the damage is quantified. The results show that changes of natural frequencies are clearly visible, thus can be used as indicator of damage presence, while the change in mode shapes can be used as the local damage indicator.