Laboratory Testing of Strengthened Cavity Unreinforced Masonry Walls

Abstract

An experimental campaign consisting of nine pressure-controlled quasi-static airbag tests on unreinforced masonry (URM) walls and accompanying material testing was completed to investigate methods for seismic retrofit of out-of-plane loaded cavity walls. Three control walls were tested to serve as a baseline for wall strength comparisons: (1) a double-leaf unstrengthened cavity wall; (2) a cavity wall with improved cavity connections; and (3) a single-leaf wall strengthened using a near-surface-mounted (NSM) fiber-reinforced polymer (FRP) strip. The experimental program was concluded by six tests that were conducted on walls strengthened using a NSM FRP strip and having cavity connections in the form of either standard bent metal ties, proprietary helical anchors, or industrial foam. The tests were designed to measure the ability of the different cavity connections to maintain the cavity gap until a ductile wall failure mechanism forms by FRP debonding. Three of the walls were previously damaged by testing in either unstrengthened or FRP-strengthened conditions. These tests were intended to study FRP retrofit effectiveness of precracked walls or the relative ability of different types of cavity connections to resist forces until a global FRP debonding occurs. For each of the six cavity connection configurations, the FRP-strengthening technique was shown to significantly improve the wall strength. The minimum strength increase was 282% compared with that of the control cavity wall. The compiled data are presented followed by general discussions on the design of seismic retrofit for cavity walls.