Evaluation of Pretensioned Girders with Partial-Strand Debonding

Abstract

Pretensioned concrete girders—especially those having large prestress forces—are susceptible to flexural cracking at their top flanges near the girder end as a result of prestress transfer. One effective method to reduce such extreme-fiber stresses is to partially debond some of the strands. The 2017 edition of AASHTO LRFD Bridge Design Specifications provides limits on the number of strands that can be debonded at a given location and in each row of strands. The limits are attributed to an experimental study in which the test specimens were designed under the previous AASHTO Standard Specifications. Some states have allowed the AASHTO limits to be exceeded, while others have adhered to the limits. National Cooperative Highway Research Program Project 12-91 Strand Debonding for Pretensioned Girders was initiated to develop a unified approach to the design of partially debonded strand details in prestressed concrete bridge girders. Detailed design case studies and synthesis of experimental data suggest that the debonding ratio is not a sufficient metric by itself to gauge the performance and capacity of prestressed concrete girders. Despite having a greater extent of debonding than the 2017 AASHTO limits, girders meeting the requirements for shear and longitudinal reinforcement in end regions are expected to perform adequately in terms of strength, deformability, stiffness, crack widths, and modes of failure.