Serviceability performance of high-strength concrete flexural members with internally unbonded post-tensioning strands

This paper introduces the experimental and analytical outcomes of eleven post-tensioned concrete members with high-strength concrete, of target cylinder compressive strength of 60 MPa. The main variables used in the study were the intensity of the applied jacking stress (fpj) and the prestressing index (ω) for three different member's span to cross- sectional depth ratios. The service performance including cracking moment, mid-span deflection at service load was studied and verified with the analytical methods recommended in ACI 318M 2019. The stress of the unbonded strands and maximum mid-span section deflection at the ultimate was also studied taking into account the change of the main variables. It was found that the ratio of the cracking moment to the ultimate moment ranged between 23.2 to 42.8 %. The ultimate moment strength was increased by increasing the amount of tensile bonded steel and the jacking stress by 45-53% and 2- 11%, respectively.