Reinforced masonry shear walls (RMSW) with masonry boundary elements (BE) are rectangular walls having integrated masonry BEs at the wall extremities. These BEs can be constructed using half pilaster block (i.e. C-shaped blocks) or regular stretchers. The compressive stress-strain response of the masonry BEs prisms built using stack-bonded C-shaped blocks (C-MSBEP) vary from that of regular stretchers prisms due to the continuity of the grout core (i.e. absence of block’s webs) and the higher grout-to-shell area ratio. Understanding and enhancing the stress-strain response of the masonry BE is a key to enhance the overall response of the RMSW with BEs. One of the challenges limiting the use of RMSW in high-rise buildings is the low compressive strength of masonry compared to reinforced concrete. Many studies showed that for specific block strength increasing the grout strength will not result in a proportional increase in the masonry prism capacity. Although some factors that result in minimizing the grout contribution to the prism strength were previously investigated, a consensus on the main governing factors is yet to be established.
In this study, the compressive stress-strain relationships of half-scale fully-grouted C-MSBEP and its constituents (i.e. masonry shell and grout core) are studied. In total, eight fully-grouted masonry BE prisms, six un-grouted masonry BE shells, eighteen grout core prisms, nine running-bonded fully-grouted stretcher block prisms, and nine stack-bonded fully-grouted stretcher block prisms have been tested under concentric compression loading. Both the un-grouted masonry shells and the grout core prisms had the same height as the grouted C-MSBEPs. The test matrix is composed of two different prisms’ aspect ratios, namely two and five. The grouted stretcher block prisms were grouted using normal strength grout while the grouted C-MSBEPs were grouted using two grout strengths, normal and high strength.
The study covers the effect of prism construction techniques in Canadian and US standards on the stress-strain response of C-MSBEPs, comparing the stress-strain of C-MSBEPs to regular stretcher block prisms, and the effect of the interaction between the masonry shell and the grouted core on the masonry compressive strength. In addition, the effect of treatment, air and wet, on the stress-strain response was also examined on the grout core prisms. Moreover, the stress-strain relationship of the 200 mm x 100 mm grout cylinders is compared to that of the grout core prisms to study the shape and size effects. The results of the grouted C-MSBEPs were compared to four predictive equations from the literature and to the unit strength values provided by the Canadian and US standards to evaluate their ability to predict the peak strength of the grouted BEs.
The stress-strain response of C-MSBEPs was found to be different from that of regular stretcher block prisms and is affected differently by height-to-thickness ratio. Thus, two analytical models were proposed to predict the full stress-strain response of C-MSBEPs and stretcher block prisms. The shape and size effects on grout core prisms are evident especially for normal strength grout. The superposition of the load-displacement response of the grout core and the masonry shell was found to be not comparable to that of the grouted BE. The effect of treatment on the stress-strain relationship of the grout cores was found to be insignificant. The equations available in the literature that were used to predict the capacity of masonry prisms were found to misestimate the experimental results of the tested C-MSBEPs. The US Masonry Structures Joint Committee (MSJC 2013) design standard was found to introduce better estimation for C-MSBEP’s compressive strength compared to the Canadian Standard Association CSA S304 (2014) “Design of Masonry Structures”. Both the CSA A179 (2014) “Mortar and grout for unit masonry” grout cylinders and the ASTM C1019 (2014) “Standard Test Method for Sampling and Testing Grout” grout prisms were found not representing the actual grout stress-strain response within the C-MSBEP, mainly because they do not simulate the effect of grout shrinkage in actual masonry prisms. Therefore, an equation was proposed that considers the different factors affecting the contribution of the grout core to the strength of C-MSBEPs.