AbstractThis paper presents experimental and numerical investigations of the shear strength of synthetic fiber-reinforced concrete (SYN-FRC) box culverts designed for fill height of 610 mm (2 ft) or less and subjected to the American Association of State Highway and Transportation Officials (AASHTO) HL-93 wheel load. Shear and flexure material tests associated with numerical analysis were conducted to obtain the material properties of concrete with compressive strength of 34 MPa (5,000 psi) and synthetic volume fraction of 0.52%. The material tests showed that the shear and flexure strength of SYN-FRC were greater than those of plain concrete (without adding fiber). The flexure material test showed that SYN-FRC can carry load even after concrete cracking, unlike the plain concrete, which collapses immediately after cracking. In addition, four full-scale SYN-FRC box culverts were tested in the laboratory, and numerical models were calibrated, using experimental data. The load was applied through a rigid steel plate at distance d from the tip of the haunch to satisfy the AASHTO HL-93 wheel load requirements. The selected load location was a critical section for the shear and imposed shear failure mode. A comparison of box culverts with and without synthetic fibers revealed that adding a synthetic fiber volume fraction of 0.52% increased the shear capacity and the ductility. All specimens failed in the shear failure mode associated with an inclined shear crack from the tip of the haunch to the middle of the loading plate. The results demonstrated that synthetic fibers can be a viable alternative to shear transverse reinforcements. Additionally, numerical verification of SYN-FRC box culverts validates the use of a concrete, brittle, cracking material model for simulating SYN-FRC in the finite-element method (FEM).