Abstract
Problem statement: Prestressed Concrete (PC) I section girder with Re inforced Concrete (RC) topping slab has been widely applied to long span bridge girders for several years. A bridge girder is subjected to severe conditions c aused 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. Deteriorat ion of the girder may be caused by a wide crack due to corrosion of the reinforcement and other mec hanisms. Prestressing force and flexural stiffness (EI) of PC-I section girder are reduced d epending 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-t ension 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 wa s applied to strengthen the damaged girder to recover its structural performance, flexural stiffn ess 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 prestressi ng force to effectively recover structural performance of a damaged girder depended directly on the damage index of the girder.
Highlights
In the 2nd test, internal prestressing force was adjusted in the analytical model to give the best agreement with experimental results as shown by Fig. 9 because the damage index changed for each test
This caused accumulated degradation of the previously tested girder leading to reduction of initial prestressing force and flexural stiffness expressed in terms of effective flexural rigidity in the test of the specimen
External post-tension was applied to recover the structural performance of the damaged test girder by varying external prestressing forces
Summary
Reinforced concrete has been developed and applied to flexural members for several decades. A crack width less than the permissible by the code of practice, can occur at service loading conditions in reinforced concrete members. This causes excessive deflection and wider cracks in long span RC structures. For example cross sectional area and moment of inertia, change from the gross to cracked section. This problem is reduced when prestressed concrete has been applied
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