Effect of high-strength concrete on web reinforcement requirements for reinforced concrete bridge girders

The objective of this research study was to evaluate the shear behavior and strength of concrete bridge members with compressive strengths in the range of 10 000 to 15 000 psi. The key objective was to determine if the current minimum amount of shear reinforcement together with maximum spacing limits in the AASHTO LRFD 2010 Specifications, and the upper limit on the nominal shear strength were applicable to concrete compressive strengths up to 15 000 psi.;Twenty tests were conducted on I-shaped specimens monotonically to failure. Sixteen specimens were reinforced concrete beams, half of them without shear reinforcement. Four AASHTO Type I prestressed concrete beams were also tested. The main variables were the compressive strength of concrete and the amount of longitudinal and shear reinforcement. Measured concrete compressive strengths ranged from 7 000 to 17 000 psi. Longitudinal reinforcement ratios on the basis of web width, rhow, varied from 1.32 to 7.71%. All specimens met the flexural requirements of the AASHTO LRFD 2010 Specifications. The amounts of shear reinforcement, rho vfyt, provided were in the range of 0 to 1 300 psi.;The findings of this research support the adequacy of the prescribed minimum amount of shear reinforcement in both the AAHTO LRFD 2010 Specifications and the ACI 318-08 Code with regard to reserve strength after first inclined cracking, and adequate crack width control at estimated service load levels for reinforced and prestressed concrete beams with concrete compressive strengths up to 15 000 psi.;The test results of reinforced concrete specimens support an upper limit for the nominal shear strength of 12√f'c in concretes with compressive strength up to 15 000 psi to prevent web crushing failures prior to the yielding of stirrups. This limit is similar to the current upper limit on the nominal shear strength in the ACI 318-08 Code.