Shear strength expression for partially grouted masonry walls

The majority of reinforced masonry constructions in the mid-western and eastern parts of the United States are partially grouted. Previous studies on partially grouted walls have shown that design provisions of the masonry standard joint committee overestimate the shear capacity of such walls. As a result of these studies, masonry standard joint committee has introduced a reduction factor in its newest version in order to overcome this problem. At 2016, the masonry standard joint committee was changed to building code requirements and specifications for masonry structures. The first part of the paper is devoted to this issue by comparing the shear strength of 42 full-scale partially grouted wall tests available in the literature with the current building code requirements and specifications for masonry structures’ shear strength expression. Results indicated that the current shear strength expression can accurately predict the shear strength of partially grouted walls with grouted cells spaced to a maximum of 1.2 m because it was developed based on test results of fully grouted walls. Unfortunately, implementing this factor has not solved the fundamental problem of the code shear strength expression for those walls with grouted cells spaced higher than 1.2 m (ordinary reinforced masonry). The over-estimation can be traced to the existence of insufficient length of horizontal reinforcement (steel effectiveness), and the assumption of linearly varying flexural strains, which the ungrouted portions of the partially grouted wall have proven unable to carry. The goal of the current study is to investigate a new, more realistic approach to the shear mechanism of ordinary reinforced masonry partially grouted walls through adopting modified infilled wall model as opposed to the monolithic wall model that already underpins the problem with the current shear strength expression. A new expression, therefore, was developed for ordinary reinforced masonry partially grouted walls based on modified infilled-frame mechanism. The shear strength predicted by the proposed model was in a good agreement with available test data including walls tested by authors.