Continuing Research on Allowable Design Release Stresses for Prestressed Concrete Beams

摘要

The maximum allowable compressive stress limit at prestress transfer is a concept that was first introduced by the American Association of State Highway and Transportation Officials (AASHTO) in the 1961 Bridge Design Specifications. The limit prescribed by AASHTO in 1961 has not changed since its inception. In the current AASHTO-LRFD (2008) Bridge Design Specifications, the requirement concerning the allowable release stress is as follows: The compressive stress limit for pretensioned and post-tensioned concrete components, including segmentally constructed bridges, shall be 0.60f'(sub ci). In the past several years, there has been significant interest in increasing the allowable limit of 0.60f'(sub ci). Relaxing the maximum allowable release stress limit has many potential benefits to the fabrication and design of prestressed girders. Some of these benefits include: (1) a decrease in the cycle time of precast facilities, (2) a reduction in the number of harped strands in a given beam, (3) a decrease in the number of debonded strands (leading to improved durability and shear performance), and (4) a longer span length due to an increased number of prestressing strands in a given cross-section. Because of these potential benefits, project 0-5197 was funded by the Texas Department of Transportation and conducted at the Ferguson Structural Engineering Laboratory at The University of Texas at Austin.