Finite-element modeling for FRP strengthening of prestressed concrete box girder bridges built by cantilever method

Balanced cantilever construction is an economical method when access from below is expensive or practically impossible. In segmental balanced cantilever construction the precast segments are transported to the bridge construction site and placed and held at the right position before post-tensioning back to the rest of the bridge. As the construction stages go on, the statically determinate structure changes to a statically indeterminate one, which should be considered in the design process. Creep and shrinkage of concrete and relaxation of prestressing steel may lead to excess long-term deflection and may cause redistributions in internal forces and stresses. In the previous study (Hedjazi et. al.) a general simulation for time-dependent analysis of segmentally erected prestressed concrete box-girder bridges has been presented. A three dimensional finite-element model for the balanced-cantilever construction of segmental bridges, including effects of the load history, material nonlinearity, creep, shrinkage, and aging of concrete and relaxation of prestressing steel was developed using ABAQUS software. The analysis has shown significant changes in the values of deflections, longitudinal stresses and internal forces as a result of longterm effects of creep and shrinkage of concrete and relaxation of the prestressing steel which has led to new arrangement and the increase in the number of mid-span continuity cables. But some times, adding new cables or rearranging the cables in existing bridges, is impossible. In these cases strengthening of the deck is a fast and economical solution. The aim of this study is to analyze the structural behavior of prestressed concrete box girder bridges when strengthening with fiber reinforced polymer laminates (FRP). Three examples of prestressed concrete box-girder bridges segmentally-erected using the balanced-cantilever technique have previously discussed to demonstrate their long-term behavior under dead load and effects of live load at the end of construction and different ages up to a thousand days by performing nonlinear analysis up to failure. In the present study, same examples of prestressed concrete box-girder bridges is being strengthened using FRP laminates. A moment-curvature analysis was subsequently carried out to investigate the flexural characteristics of the prestressed concrete box-girder bridges prior to and after strengthening with CFRP laminates. The results shows that significant strength can be gained at the ultimate limit state. The increase in flexural resistance at ultimate does provide an adequate margin of safety against further overloading.