Replaceable Unbonded Tendons for Post-Tensioned Bridges: Fid-Bau Portal

Replaceable Unbonded Tendons for Post-Tensioned Bridges

H. R. Hamilton / J. A. Rice / A. Abdullah / R. Bhatia / N. Brenkus / D. Skelton

Prestressed concrete is widely used as a cost-effective and efficient method of bridge construction and offers a number of unique advantages over other systems. Florida Department of Transportation (FDOT) is implementing the use of flexible fillers in lieu of cementitious grout in certain post-tensioning tendon profiles. This research was divided into three areas of focus. The first area of work involved the design, construction, and injection of full-scale post-tensioning tendon mockups. Five 200-ft long specimens were fabricated with a profile that simulated both internal and external tendons. HDPE duct of 4-in. diameter with nineteen 0.6-in. prestressing strands formed the tendon. Injection rates and venting procedures were varied among the five mockups, primarily in an effort to determine the most suitable approach. Based on constructability tests conducted, no cause to restrict use of any of the PT systems or filler products was found. The second area of research was on the structural implications of the change to flexible fillers. This part of the research project focused on the flexural strength behavior of specimens with internal and external tendons using AASHTO Type IV sections. It was found that the AASHTO-LRFD design specifications adequately predicted the flexural strength of members with external unbonded tendons with flexible fillers. In addition, fatigue specimens were constructed to test the fatigue performance of the unbonded tendons with diabolo deviators. Duct damage was noted at one of the deviator exit locations that was the result of the strands pinching the HDPE wall against the concrete. Providing sufficient flare curvature in the deviator was critical for good performance. The third area of research focused on developing a robust and cost-effective monitoring system for unbonded post-tensioning tendons. The change from bonded to unbonded tendons allows a unique opportunity to develop an efficient system for tendon damage detection with the ultimate goal of providing maintenance decision support. Analytical and experimental investigations were performed to develop an algorithm that can be used to detect, locate, and quantify tendon damage by monitoring the strain distribution in the wedge plates of the anchors.