System identification and damage detection of a prestressed concrete beam

In the domain of civil engineering it is often necessary to monitor constructions such as buildings or bridges to maintain safety conditions. Nondestructive test methods outmatch other methods, because they do not influence the constructions performance. One approach is based on the experimental determination of modal parameters (eigenvalues, damping, mode shapes). From the changes in modal data damage can be detected. By updating a reference finite-element model such that its numerical modal data correspond well with the experimental modal data of the damaged structure, the damage pattern can be identified. When applying this technique to prestressed concrete, the problem arises that, because of the prestressing, cracks close again. Therefore a research program was started to investigate the change of modal parameters of a gradually damaged prestressed concrete beam. Static loads with increasing amplitude were applied. In between each load step a dynamic measurement was performed. The results show that the damage detection remains difficult for prestressed concrete in the early damage state. However, a damage pattern could be identified, which corresponds to the locations of the final failure.