AbstractTo fully recognize the load-resisting mechanisms of post-tensioned concrete (PC) structures with realistic boundary conditions against disproportionate collapse, four beam-column subassemblies were extracted from a prototype building and the side columns and joints were reproduced to reflect the actual boundary condition. The parametric analysis was conducted, including location of the removed column (middle or penultimate) and strand profile (straight or parabolic). In addition, two RC counterparts were tested as a control group. Test results indicate that the unbonded post-tensioning strand (UPS) was able to enhance the structural robustness by increasing compressive arch action capacity of RC beams and developing catenary action. Compared with RC specimens, both PC specimens achieved much higher load resistance; herein, the PC specimen with straight strand profile obtained the highest load resistance due to two strands used, while the PC specimen with parabolic profile had higher deformation capacity. However, the existence of UPS increased the tensile force demand to the side column, leading to the flexural tension failure of the side column when the loss of a penultimate column was considered. Finally, an analytical study was carried out to quantify the load resistance from each dominant load-resisting mechanism.

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