Strengthening a 20-Year-Old Post-Tensioned Concrete Box Beam with Double-Layer Prestressed Steel Wire Ropes

Overloading, corrosion, and material aging deteriorate the structural performance of prestressed concrete (PC) bridges. Strengthening techniques are needed to improve the serviceability and extend the life of these deteriorating bridges. This study examined a strengthening technique with double-layer prestressed steel wire ropes (PSWRs) to enhance the serviceability of an existing post-tensioned concrete box beam for the first time. The tested box beam was removed from a demolished 20-year-old bridge. The service-level behavior of the beam, before and after strengthening, was evaluated using four-point flexural loading. The enhancement effects of the double-layer PSWR on the service-level behavior of the beam are discussed, including details on deflection, crack width, and reinforcing steel stress. Results show that PSWR strengthening is a feasible method for improving the serviceability of post-tensioned concrete box beams. The restraining effect of PSWR on crack development is more significant than the effect on deflection and reinforcing steel stress. Crack width, deflection, and reinforcing steel stress under the code-specified service load decreased by 50, 23, and 21%, respectively, after strengthening.