Behavior Evaluation of Existing Plate Girder Bridge Strengthened with External Prestressing Tendons (05-2464)**
Cheolwoo Park, Kangwon National University, South Korea
Jongsung Sim, Hanyang University, South Korea
Young Hoon Park, Bucheon College

In this study the effect of strengthening on in-service plate girder bridge by means of external prestressing tendons was investigated. The loss of prestressing force with time was investigated while the existing prestressing force was released/re-prestressed. Also a field load test was performed using a live-truck load to evaluate the behavior of the bridge before and after the strengthening. An additional numerical model using FEM was developed and used in the analysis. From the experiments, it was found that the long term loss of prestressing force on the external tendons was negligible and that the strengthening did not significantly affect the dynamic responses of the bridge. However, the strengthening reduced the mid-span deflection by 10-24% and also improved the fatigue resistance and the torsional rigidity of the bridge. The torsional rigidity enhancement arising from the strengthening became more apparent as the truck speed increased. The natural frequencies from the field load test, FEM analysis and suggested formula showed good agreement. It was also found from the dynamic load test that the strengthening did not significantly influence the natural frequency and impact factor.