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One of the uncertain damage parameters to jeopardize the safety of existing PSC bridges is the loss of the prestress force. A substantial prestress-loss can lead to severe problems in the serviceability and safety of the PSC bridges. In this paper, a nondestructive method to detect prestress-loss in beam-type PSC bridges using a few natural frequencies is presented. An analytical model is formulated to estimate changes in natural frequencies of the PSC bridges under various prestress forces. Also, an inverse-solution algorithm is proposed to detect the prestress-loss by measuring the changes in natural frequencies. The feasibility of the proposed approach is evaluated using PSC beams for which a few natural frequencies were experimentally measured for a set of prestress-loss cases. Numerical models of two-span continuous PSC beams are also examined to verify that the proposed algorithm works on more complicated cases.

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In this study, a vibration-based method to simultaneously predict prestress-loss and flexural crack in PSC girder bridges is presented. Prestress-loss and flexural crack are two typical, but quite different in nature, types of damage which can be occurred in PSC girder bridges. The following approaches are implemented to achieve the objective. Firstly, two vibration-based damage detection techniques which can predict prestress-loss and flexural crack are described. The techniques are prestress-loss prediction model and mode-shape-based crack detection method. In order to verify the feasibility and practicality of the techniques, two different lab tests are performed. A free-free beam with external unbonded tendons is used to verify the feasibility of the prestress-loss prediction model. In additional, a PSC girder with an internal unbonded tendon is used to evaluate the practicality of the prestress-loss prediction model and the modeshape-based crack detection method.

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