Pre-stressed steel strips for the strengthening of axially loaded masonry walls

Abstract

The current paper presents an experimental investigation on the working mechanism of pre-stressed steel strips, used for the strengthening of brick masonry walls when subjected to axial loads. Three strengthening schemes were used, involving vertical and in some cases horizontal strips, with or without pre-stress, installed onto the walls through binding bolts. A total of nine unreinforced masonry walls were prepared and tested up to failure, by using the level of pre-stress on the steel strips as well as the axial preload level on the walls, as parameters. The test results showed that pre-compression on the vertical strips increases the crack initiation and the crack distribution loads by percentages as high as 60%, and 50% respectively, whereas the level of preloading, not resulting in the initiation of cracking, do not play a significant role in the overall behavior of the walls. Pre-tension on the horizontal steel strips on the other hand, controls the behavior of masonry at the ultimate limit state and increases the axial load bearing capacity of the walls by almost 43%. Moreover, the pre-tension on the horizontal strips, enhances the lateral support conditions of the vertical counterparts and changes the post-buckling behavior from unstable to stable. In general, the intervention scheme which involved pre-stressing in the horizontal strips performed better, in terms of the ultimate and the serviceability limit states. Based on the observed behavior of the strengthened walls, a design procedure is proposed with the use of a failure criterion for bi-axially compressed anisotropic masonry.