ABSTRACT
The shear and torsion design provision of the Australian Bridge Design Standard AS5100.5 has been revised significantly in 2017 and is now based on the Modified Compression Field Theory (MCFT). The MCFT approach is based on the equilibrium, compatibility and stress-strain characteristics of cracked concrete. The previous Australian Standard provisions, based on the parallel-chord truss model, considered the design effects of shear and torsion separately and are added later for reinforcement calculations. The cracked concrete capacity is also ignored under high shear and torsion. This is inconsistent to the true beam behavior and could lead to unsafe results for certain beams or underestimated capacity in other cases.
The Australian bridge stock includes bridges designed or strengthened to previous national design Standards including, apart from the recently replaced AS5100-2004, the Australian Bridge Design Code ABDC 1992 and the National Association of Australian State Road Authorities NAASRA 1976 Standard. The question that arises at this moment is where do these bridges stand as to their shear strength compared to a more consistent and accurate Standard provision and does the new Australian Standards’ shear provision really indicate any strength issue that needs to be addressed? A review of the main areas of differences with the previous Standards provisions is presented in this paper with a comparison with those of other international Standards, mainly the AASHTO and the Canadian Standards. Comparison is also made with tested capacities of a limited number of published test results. Areas of major differences with the previous Standards that may affect the existing bridge stock are highlighted and a conclusion is drawn.
