Recent Changes to Concrete Shear Strength Provisions of AASHTO-LRFD Bridge Design Specifications

Abstract

Based on the results of the foregoing studies the AASHTO LRFD Specifications for the 4 th Edition were revised as follows: 1 The limit of 10 ksi on the concrete compressive strength that could be used for shear design in the LRFD Specifications through the 3 rd Edition was raised to 18 ksi. 2 The limit on the maximum shear stress for shear design was reduced from 0.25f' c plus the effect of the vertical contribution of the prestress force to 0.18f' c plus the effect of the vertical contribution of the prestress force. However, the value of 0.25f' c can continue to be used if the beam is built integrally into its support at the end so that it is fully supported over its depth at the end, or if the end region is designed by strut and tie modeling. 3 Provisions were introduced for checking for shear cracking since shear stresses in excess of 0.15f' c can result in shear cracking and localized stirrup yield under service load levels. 4 The option for the use of the staggered shear design method away from the support region has been removed. 5 Simplified provisions were introduced for the design of beams, prestressed and non-prestressed, that contain at least the minimum required amount of shear reinforcement.