Effective axial strength of laterally strengthened RC pier heads with post‐tensioning method

This study investigates the structural performance enhancement of reinforced concrete (RC) pier heads laterally strengthened with unbonded post‐tensioning (PT) to accommodate increased design loads following a deck replacement of an existing railway bridge. A nonlinear finite element (FE) analysis was performed to examine the active confinement effect introduced by PT and its influence on axial load capacity and compressive behavior of deteriorated pier heads. Two FE models—a detailed model and a simplified model—were developed to assess modeling accuracy and computational efficiency. The simplified model showed only a 3.5% difference in peak load compared to the detailed model, confirming its suitability for extensive parametric studies requiring multiple simulations. A parametric analysis considering PT stress levels, tendon layouts, and strengthening zones demonstrated that PT strengthening increased the ultimate axial load capacity by approximately up to 83% and enhanced the maximum compressive stress of the existing concrete by up to 115%. Furthermore, PT shifted the failure mode from brittle to quasi‐ductile, indicating significant improvement in deformability and post‐peak behavior. Based on the FE results, confinement and effective strength coefficients were derived to facilitate practical design applications. A design‐oriented approach for estimating the confined compressive strength of the strengthened pier head was proposed, together with recommended PT stress levels of 500–734 MPa and an optimal strengthening zone limited to the upper section of the pier head, extending down to a depth equal to its width. These outcomes provide a rational and practical framework for applying unbonded PT strengthening to RC pier heads and contribute to improved methodologies for bridge rehabilitation.