Deformation and cyclic buckling capacity of external replaceable hysteretic dampers for unbonded post-tensioned precast concrete walls

This paper proposes and validates a type of external replaceable hysteretic dampers to be mainly applied to unbonded post-tensioned (UPT) precast walls. The main aim of the proposed damper was to provide the UPT walls with large energy dissipation without significant buckling. To evaluate the efficiency of these dampers, a cyclic test was conducted. The damper specimens consisted of a mild steel round bar with a reduced diameter over a fused length and an additional threaded length at each side, for installation purposes. Moreover, a round steel tube was installed over the fused length and filled with grout to delay the buckling. The proposed dampers, with different geometries and conditions, were subjected to cyclic loads to evaluate their deformation capacity and fracture mechanism. The specimens displayed a regular and stable hysteretic curve until strains of 9%, after which a flexural buckling was observed at the ends of the fused length. However, this flexural buckling did not affect the energy-dissipating capacity in any specimen. Consequently, this type of damper is considered suitable for applications in self-centering rocking walls. Furthermore, the proposed dampers fractured by a combination of low-cycle fatigue and excessive rotations at the transition length. In addition to the experimental validation, an extensive numerical investigation was conducted on the proposed damper to complement the experimental data and to provide analytical tools for design.