Flexural Behavior of Posttensioned Concrete Beams with Unbonded High-Strength Strands

This paper assesses the applicability of high-strength strands to current design codes and various existing equations. To evaluate the flexural performance of posttensioned concrete members with Grade 2400 strands, a flexural experiment was conducted on eleven specimens. Test variables included the tensile strength of strands, the number of strands, the cross-section shape, and anchorage zone reinforcement details. The test results were compared with ACI 318-19, AASHTO, and equations of Du and Tao, Naaman and Alkhari, and Harajli to evaluate the applicability of flexural strength equations for posttensioned concrete members using unbonded high-strength strands. Results indicated that the provisions of ACI 318-19 and AASHTO design codes and the existing equations underestimated the increased stress of the high-strength strands. Additionally, results demonstrate that improved equations are needed to consider the strain-compatibility model, plastic hinge length, and relationship between bonded reinforcement, concrete, and prestressing steel in posttensioned members using high-strength strands.