Flexural Behaviors of Damaged Full-Scale Highway Bridge Girder Strengthened by External Post Tension

Problem statement: Prestressed Concrete (PC) I section girder with Reinforced Concrete (RC) topping slab has been widely applied to long span bridge girders for several years. A bridge girder is subjected to severe conditions caused by an aggressive environment and overloading. A crack can be initiated and propagate when the tensile stress exceeds the tensile strength of concrete due to overloading. Deterioration of the girder may be caused by a wide crack due to corrosion of the reinforcement and other mechanisms. Prestressing force and flexural stiffness (EI) of PC-I section girder are reduced depending on the level of overloading and the corresponding damage. Approach: Full scale tests of Type III AASHTO highway girder with a 20 cm thick RC topping slab were performed to study both the degradation process due to overloading and also the effects of external post-tension in the recovery of structural performance of a damaged highway PC bridge girder. Results: The results showed that degradation, loss of internal prestressing force in the PC-I girder and flexural stiffness of the composite girder depend directly on Damage Index (DI) expressed in terms of permanent deformation. External post tension with three levels of prestressing forces was applied to strengthen the damaged girder to recover its structural performance, flexural stiffness and strength. A simplified analytical model, verified by test results, was developed to predict flexural behaviors, loss of internal prestressing force and flexural stiffness of highway girder due to overloading and also structural performance of the strengthened girder. Conclusion: It was found that the required external prestressing force to effectively recover structural performance of a damaged girder depended directly on the damage index of the girder.