6．Prediction method for damage location at PC girders due to rapture of main tendon and corresponding reinforcement

Prediction method for damage location due to cutting of main tendon at PC girders was developed.
The predicted damage zone was partially reinforced with the proposed method employing steel plates.

Pre-stressed concreted (PC) girders are made of concrete containing a pre-stressed steel tendon (tendon) and have been generally used for relatively long span bridges. In recent years, the grouting (cement-milk) used to protect the tendons has been found to be insufficient in sheath, leading to tendon rupture and decrease of loading capacity of PC girder.

The study was proposed a model for expressing the bond stress(τ）-slip (s) relationship based on the laboratory test, which including the effect of material and shape of tendons. The developed model was used for calculating the resistance of damaged PC girders as well as the location of damaged zones. This system will produce a reinforcing planning for deteriorated PC beams (Fig.1).

In addition, the partially reinforcing method at the predicted damage zone by using steel plates was developed, using expansion anchors without deep drilling. Conventionally, the external reinforcement strands has been added as a reinforcing method. Compared to the method, the proposed method is easier to execute, can prevent curving up of the girder by adding tendons which influences train running, can be easily applied to narrow working areas under PC girders, and can prevent from damaging the intact tendons by installing anchors.

The abovementioned advantages already confirmed by the experiment with full size PC girders (Fig.2).

Fig.1 Force transfer model based on bond and damage prediction
Fig.2 Partially reinforcement work and resulting effect