Shear Strengthening of Full-Scale Precast Concrete Box Culvert Using Bonded FRP Panel

The shear capacity of underground box culverts decreases with increasing service life. Removing the soil above and enlarging the section are restricted. Bonded fiber-reinforced polymer (FRP) strengthening is suitable for these conditions, but full-scale verification remains limited. For this reason, the shear performance of a box culvert strengthened with an FRP panel was analyzed in full-scale tests. The initial cracking load increased to three times that of the control test unit. The deflection at the ultimate load decreased by 50.4%. The yield load of the steel reinforcement in the wall increased by 38%. A nonlinear finite element model predicted the initial cracking and ultimate loads with an error of no more than 4%. A parametric study was conducted on the concrete compressive strength, the panel thickness, and the strengthening of the haunches. As a result, the ultimate load decreased by only 21.5% when the compressive strength was lowered from 35 MPa to 15 MPa. A thicker panel mainly increased the initial cracking load, whereas extending the panel across the haunches increased the ultimate load by 4.6%. Bonded FRP strengthening improves the shear performance of a box culvert and remains effective in deteriorated concrete.