Damage controlling performance of unbonded post-tensioned precast concrete walls

Damage to non-structural walls has been considered as one of problematic damages to reinforced concrete members since 1990's. Damage to non-structural walls is not critical to save buildings from collapse but its impact on the building function is nearly as critical as damage to structural members. The cost to repair, to compensate downtime, and to recover credibility differs dramatically for buildings with and without non-structural wall damage. This paper demonstrates superb quick recovery performance of unbonded post-tensioned precast rocking wall from both experimental and numerical view points in order to alleviate the impact of non-structural wall damage and to take advantage of its self-centering capability. Firstly, quick recovery performance of two unbonded post-tensioned precast concrete (UPT-PC) walls was reviewed. Two UPT-PC walls, tested in Tokyo Institute of Technology in 2015, were 1800mm tall with cross sections of 200 x 1100mm (NSW6A) and 200 x 450mm (NSW7A). The test was carried out under cyclic static lateral loading with constant axial load. Both specimens showed excellent quick recovery performance with negligible residual drift and cracks. The damage level of specimens was evaluated using four limit states listed in the 2015 AIJ draft for structural design and construction of prestressed concrete buildings on performance evaluation concept guidelines. The determining factor for each limit state was mostly governed by compressive damage of concrete. It was found that the compressive damage of concrete occurred when the average compressive strain of concrete reached much higher than that based on the existing theories; for example, strain was 0.4% for compressive crack, 0.78% for cover spalling, and 1.13% for crushing of cover concrete for NSW7A. Secondly, the behavior of walls was numerically simulated with a multi-spring model. Assuming the damage length in compression is half of the wall length, the multi-spring model accurately simulated hysteresis loops of load-drift relation and tendon force - drift relation for both specimens, leading to relatively precise simulation of residual drift and equivalent damping ratio. The numerical model was able to evaluate the timing and determining factors of each limit state. As a result, detailed damage levels of analyzed walls were successfully classified to have a good agreement with experimental results. The results of numerical analysis, in addition to the experimental results, demonstrated the superb quick recovery performance of the unbonded post-tensioned precast rocking wall. © 2018 Architectural Institute of Japan. All rights reserved.