Improved Beam End Reinforcement Details for PCBTs with Debonded and/or Draped Strands

About the project:

Cracks can form in the end regions of prestressed concrete girders as the force in the prestressing strands transfer to the surrounding concrete as the strands are released, resulting in tensile forces normal to the direction of the prestressing force. This problem can be more prevalent in deeper members and those with draped or larger diameter strands. VDOT requires that cracks wider than 0.002 inch be repaired. Such repairs necessitate additional time, effort, and money. To counteract these cracks, VDOT implemented the design approach recommended in a2009 VTRC report. However, the reinforcement details that result from this design lead to congestion, which hinders proper concrete consolidation during fabrication, which, in turn, leads to strength and integrity issues during service.

Unlike VDOT, other DOTs have wider crack limits, or they permit tendon debonding or splayed draped tendons to mitigate end zone cracking. Alternatively, welded grid reinforcement, consisting of smooth horizontal wire welded to deformed vertical bars, can have shorter development lengths that may allow larger reinforcement stresses and enable less congestion in the end region.

This project seeks to develop new standard reinforcement details in the end regions of PCBT beams that reduce the current level of congestion while continuing to prevent cracks in these regions during strand release. The expected details should include tables and drawings for optimized welded grid reinforcement and/or draped or straight debonded tendons that can be used for design, bidding, and construction for the range of PCBT beams in VDOT’s inventory. Additionally, the research should provide guidance regarding increasing the stress limit for the mild reinforcing within this portion of the girders. These objectives will be achieved through a literature review and DOT survey of current practices, finite element modeling, and small- and large-scale tests.

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