Strategies to Reduce and Quantify Seismic Damage in Controlled Rocking Masonry Walls

Abstract

Controlled rocking systems have been used in numerous structures around the world as a seismic force-resisting system. In a controlled rocking wall system, the wall is allowed to uplift from the foundation during seismic events, thus reducing the wall’s lateral stiffness and minimizing its corresponding seismic force demands. This rocking mechanism is often controlled using posttensioning (PT) tendons, resulting in negligible residual deformations compared to conventional walls (i.e., with fixed bases). For these reasons, promising strides have been taken to apply the concept of controlled rocking systems to masonry walls; however, several issues have been encountered when using PT tendons due to the brittle nature of the masonry material in compression. To address this, the current study aims to reduce damage and improve the performance of controlled rocking masonry walls (CRMWs) by omitting PT, instead relying on gravity loads and energy dissipation to control the seismic response. Three strategies to achieve this improved performance are proposed and investigated. The first strategy involves using externally mounted, replaceable energy dissipation devices; the second strategy introduces a steel base for the rocking wall; and the third strategy considers confinement plates in the rocking toe region of the wall. To assess these strategies, the study develops and validates a numerical model to capture the performance of previously tested CRMWs. The model is then used to develop and experimentally validate an index for masonry walls to quantify their damage based on numerical results. Next, a suite of 20 CRMWs is designed, 5 of which incorporate PT tendons while the remaining 15 walls omit PT and incorporate one or more of the proposed strategies to reduce damage. Numerical models of all of the archetype walls are subjected to reversed cyclic loading protocols, and the amount of damage incurred is compared across each archetype wall. The results demonstrate that the proposed modeling technique and damage index are effective at capturing the response and quantifying damage in CRMWs and that the proposed strategies result in a lower damage alternative to posttensioned CRMWs (PT-CRMWs).