Shear Strength and Behavior of Prestressed Concrete Beams

An experimental study was conducted at the Phil M. Ferguson Structural Engineering Laboratory at the University of Texas at Austin to investigate possible shear performance issues for the new family of Tx girders. A comprehensive literature review revealed that similar I-shaped girder sections and Bulb-Tees are prone to fail in a horizontal sliding shear mode, where the bottom flange tends to slide in against the bottom flange-web interface. Due to the increased flange width to web width ratio of the new Tx girders, there is reason to think that the horizontal sliding shear mode can govern the behavior of the Tx girders, compromising the safety margin of current bridge designs. The goals of this research project were:

• to investigate the applicability and conservativeness of current shear design provisions when applied to the Tx girders,
• to evaluate the overall shear performance of the Tx28 girder under the worst case scenario service loads, and
• to incorporate the results of this experimental program into the University of Texas Prestressed Concrete Shear Database

To achieve these goals, shear tests were conducted on two ends of two full scale Tx28 girders, resulting in a horizontal sliding shear failure mode in all cases but still yielding conservative results with the use of current shear design provisions from ACI-318 (2008), the AASHTO LRFD Bridge Design Specifications (2007) and the AASHTO Guide for Design and Construction of Segmental Concrete Bridges (Interim 2003).

In the light of the results from this experimental program and several others included in the University of Texas Prestressed Concrete Shear Database, recommendations for current shear design provisions were made.