Simplified Method for Shear Design of Prestressed Concrete Girders

Abstract

The new AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications incorporate the modified compression field theory for shear design of prestressed and non-prestressed concrete members. This method is based on the variable-angle truss analogy model and takes into account the inclination of diagonal shear cracks, the strain in longitudinal steel, and the applied shear stress on a section. This is a realistic approach to predict the shear resistance of any section of a concrete member. However, for prestressed concrete sections, an iterative process is required in conjunction with charts and tables to determine the shear resistance of the sections. The process is cumbersome and time consuming. In an effort to simplify the process, Washington State Department of Transportation has completed a parametric study that results in a simplified method of using fixed shear design parameters. The simplified method saves significant time in shear design of prestressed girders, especially when it is used to standardize the shear reinforcement in a series of standard prestressed concrete girders.

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