Refinement of numerical models to reproduce shear force-deformation backbone curves of unbonded precast post-tensioned concrete members

Damage reports from recent major earthquake events indicate that even when buildings do not collapse, damage to beams and columns makes continued use of the building difficult. Due to large socioeconomic losses resulting from past major seismic events, modern buildings are expected to maintain their functionality during and after earthquakes. Among the promising structural systems to achieve such performance is the unbonded precast post-tensioned concrete (PCaPT) system. Although extensive research has been conducted both domestically and internationally, the inelastic behavior of unbonded PCaPT members is not fully understood. This study aims to refine analytical models to reproduce flexural behavior of unbonded PCaPT members. A multi-spring model incorporating a stress–strain relationship of concrete considering compressive fracture energy was developed and applied to simulate the flexural performance of 25 beam specimens. From the analytical results, the following findings were confirmed: (i) the shear force – deformation backbone curve was accurately reproduced regardless of variations in the plastic hinge length by using the compressive fracture energy of concrete, (ii) the behavior of prestressing tendons for specimens with relatively high prestressing levels was reproduced up to a member drift around 10%, including during unloading, and (iii) the axial elongation of specimens with low prestressing levels was reproduced with high accuracy.