Dynamic testing of precast, post-tensioned rocking wall systems with alternative dissipating solutions

TLDR

Over the past two decades, the focus has been on providing communities with cost‑competitive structures that sustain minimal damage during earthquakes, prompting the development of high‑performance seismic‑resisting systems and advanced design methodologies. The study investigates the effectiveness of velocity‑ and displacement‑dependent dissipation in four pre‑cast, post‑tensioned rocking wall systems tested on a shake‑table, aiming to protect against far‑field and velocity‑pulse ground motions. The walls were designed as retrofit solutions for an existing frame building using a performance‑based strategy, with dissipation provided by externally mounted devices parallel to post‑tensioned tendons, and each wall incorporated either viscous fluid dampers, tension‑compression yielding steel dampers, a combination, or no devices, allowing easy replacement or inspection after an earthquake. Experimental results show that maximum displacements and material strains remained within acceptable limits, residual deformations were minimal thanks to re‑centring by the tendons, and damage was confined to inelastic yielding or fluid damping of the external dampers.

Abstract

During the past two decades, the focus has been on the need to provide communities with structures that undergo minimal damage after an earthquake event while still being cost competitive. This has led to the development of high performance seismic resisting systems, and advances in design methodologies, in order respect this demand efficiently.
 This paper presents the experimental response of four pre-cast, post-tensioned rocking wall systems tested on the shake-table at the University of Canterbury. The wall systems were designed as a retrofit solution for an existing frame building, but are equally applicable for use in new design. Design of the wall followed a performance-based retrofit strategy in which structural limit states appropriate to both the post-tensioned wall and the existing building were considered.
 Dissipation for each of the four post-tensioned walls was provided via externally mounted devices, located in parallel to post-tensioned tendons for re-centring. This allowed the dissipation devices to be easily replaced or inspected following a major earthquake. Each wall was installed with viscous fluid dampers, tension-compression yielding steel dampers, a combination of both or no devices at all – thus relying on contact damping alone. The effectiveness of both velocity and displacement dependant dissipation are investigated for protection against far-field and velocity-pulse ground motion characteristics.
 The experimental results validate the behaviour of ‘Advanced Flag-Shape’ rocking, dissipating solutions which have been recently proposed and numerically tested. Maximum displacements and material strains were well controlled and within acceptable bounds, and residual deformations were minimal due to the re-centring contribution from the post tensioned tendons. Damage was confined to inelastic yielding (or fluid damping) of the external dampers.