The behavior of an in-service plate girder bridge strengthened with external prestressing tendons

In this study the effect of strengthening on a bridge by means of external prestressing tendons was investigated. The target bridge was a plate girder bridge which had been in service for 23 years before the strengthening. The loss of prestressing force with time was investigated while the existing prestressing force was released/re-prestressed after four years of service since the strengthening. 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 the finite element method was developed and used in the analysis. From the experiments, it was found that the long term loss of the 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%. The strengthening also reduced the difference in deflection between girders while the truck was riding on the outer girder and this difference arising from the strengthening became more apparent as the truck speed increased. It was also found from the dynamic load test that the strengthening did not significantly influence the natural frequency and impact factor.