Performance of segmental post-tensioned concrete girders with minimum flexural reinforcement

Eull, Jacob
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The main purpose of the minimum flexural reinforcement requirement is to ensure that a structural member possesses sufficient strength and ductility. If the minimum requirement is not met, the structure is subject to fail in a brittle manner, without adequate warning or redistribution of load, when it reaches the flexural cracking limit state. The current AASHTO LRFD Bridge Design Specifications minimum reinforcement requirement addresses this by ensuring a minimum ratio between the flexural nominal moment capacity and flexural cracking moment at the section level. This is an iterative process, which in some cases is never satisfied regardless of the amount of reinforcement provided within the structure. Additional methods for determining minimum reinforcement, such as Leonhardt’s method, are commonly utilized in practice. However, these processes make assumptions that are not relevant in many current girder section designs.

To address these concerns, an experimental research project (NCHRP 12-94) was conducted to examine the current AASHTO LRFD Bridge Design Specifications on the minimum flexural reinforcement and improve the effectiveness of the requirement. This thesis will focus on the segmental post-tensioned concrete girder experimental study conducted as part of NCHRP 12-94. These test girders were designed at various reinforcement amounts, both above and below the minimum reinforcement requirement. The objective of this thesis is to establish better understanding of the overall performance of the girders, as well as provide complimentary analysis to ensure sufficient strength and ductility. From the experimental study, all test girders showed adequate strength and ductility beyond the cracking limit state. Additionally, it was consistently observed that the segmental post-tensioned girders with unbonded tendon experienced an overall behavior shift from flexural theory response to a hinging mechanism response amidst the formation of a concentrated crack adjacent to the midspan section’s joint. Based upon this observed behavior, an analytical method is proposed and validated with the experimental results to ensure adequate strength and ductility of a designed segmental post-tensioned girder.

flexural, minimum, post-tensioned, segmental