Study of a Slender Masonry Wall Tested in an Innovative Device
Creators: Gonzalez Mariscal, Rafael De Jesus
Publisher: name: University of Alberta Library
Year: 2022

<p>Slender masonry walls are often found in school gymnasiums, warehouses and other low-rise buildings. According to current North American masonry design standards, a slender wall is defined to have a height-to-thickness ratio of 30 or greater. These walls must satisfy several stringent requirements as they are more susceptible to second-order effects, and it is believed that they present early instability issues. However, only a few experimental tests have been conducted to understand the true nature of slender masonry walls. Moreover, recent studies show that provisions in the standards are overly conservative and lead to non-economical designs. This study is the starting point of a research campaign that aims to address the need for more experimental tests on full-scale slender masonry walls.</p>

<p>A numerical model using the software OpenSEES proved to closely predict the response of slender masonry walls subject to a combination of vertical and out-of-plane loads. The model was used to perform a parametric study to understand the behaviour of these walls under a variety of conditions and propose a promising solution to increase the stiffness of concrete masonry walls. Results of the parametric study also showed that walls were unstable shortly after the reinforcement yielded, suggesting that the requirement of a ductile failure mode in the standards should be re-evaluated. Then, an 8.75 m tall concrete masonry wall was built on a specially designed test setup. The wall was tested under a combination of vertical and cyclic out-of-plane loads, and under pin-end conditions. The importance of having a displacement limit in the standards was evident after pushing the wall to a midspan displacement equal to the serviceability limit of h/180 (48 mm) required by S304-14. After unloading, the residual displacement at midspan was already equal to 8 mm, indicating some damage and loss of out-of-plane stiffness. After a few cycles and when the sensors had indicated yielding of the vertical reinforcement, the test was stopped.<br>
Sensor readings showed that the maximum moment was not located at midspan but higher. This suggests that different loading conditions may have been present in the test, such as a differential pressure applied by the airbag or some friction present on the pinned supports. It was also found that the neutral axis was within the face shell of the concrete block from the early stages of loading. This means that the grouted portion of the cross-section contributed very little to the wall response, probably only before cracking. It also shows that the ungrouted properties of the masonry are highly relevant for the response of these walls.</p>

<p>The behaviour of the wall after cracking was mainly affected by the area and location of vertical reinforcement. If the vertical bars were defined as centrally located in the cross-section of the numerical model, the wall stiffness was underestimated when compared to test results. This may be explained if steel bars were deviated from their original position farther from the compressive face of the wall during the grouting process, resulting in a larger post-cracking stiffness and a larger yielding load.</p>