Self-centering behavior of unbonded precast concrete shear walls

Concrete shear walls are a cost-effective way of providing lateral load resistance for structural systems located in seismic regions. If concrete shear walls are precast and rely on unbonded post-tensioned tendons for flexural reinforcement, then the structural damage observed in conventionally reinforced cast-in-place shear walls arising from tensile stress transfer can be avoided altogether. Over the past decade, it has been recognized that excellent seismic performance of precast concrete shear walls can be mobilized by utilizing post-tensioned unbonded vertical reinforcement in precast shear walls to create extensible connections that allow controlled rocking. Another important advantage of post-tensioned precast concrete shear walls, and one which has not been studied extensively, is their superior self-centering characteristic. The self-centering property of unbonded post-tensioned walls is generally attributed to the presence of the post-tensioning force. However, the experimental results presented in this study indicate that the post-tensioning force may completely die out during cyclic loading while the wall retains its self-centering characteristic. Moreover, analytical study, verified with experimental results, indicates that with proper design of end-anchorages for post-tensioned tendons, self-centering can be achieved even when the post-tensioning force dies out completely. The study summarized here investigates the self-centering ability of unbonded precast concrete shear walls, particularly the effects of post-tensioning force, tendon layout, and the end-anchorage detail.