# Effect of Thin Cement-Based Renders on the Structural Response of Masonry Wall Panels
## 4 Results and Discussion
### Results and Analysis of Shear Tests  
Eight square wall panels were tested in shear (diagonal tension test). Stone and brickwork panels were tested in both rendered and non-rendered conditions. Results of the shear tests are reported in Table 4.  
Contrary to compression tests, ultimate strengths were noted to have significantly increased when a cement-based render was utilized (Figure 8). Interestingly, these shear strengths (\(\tau_{0}\)) were higher--on the order of 0.081 and 0.165 MPa for stone and brickwork panels, respectively--than was expected considering the existing literature. With regard to the softening branch of the response curves shown in Figure 8, limited qualitative information is available from the tests. Tests were carried out using hydraulic jacks with little control on the displacement rate. For stone non-rendered masonry panels, the maximum loads are similar in magnitude to the ultimate load (residual strength). This is typical for masonry of low quality [38]. The softening branch of the rendered stone and brick panels was slightly different with a larger reduction in strength. The Italian Building Code (Guidelines [37]) and the long experience of the authors [13; 14; 22] demonstrate that the shear strength of an irregular double-leaf stone wall is rarely higher than 0.03-0.04 MPa. All un-rendered stone work panels exhibited a shear strength in the range of 0.022-0.036 MPa (Figure 9). The average value of the shear strength was for these panel 0.0283 MPa. A similar comment could be made about the results of tests on brickwork panels. The results of the rendered panel is again significantly higher than expected. By comparing this result with the one for the un-rendered panel, it can be noted that the contribution of the cement-based render seems to be critical. Typical cyclic behaviour for both non-rendered and rendered wall panels is shown in Figure 8b. As can be seen from this figure, because of the cement-based render, panels cut off from Building No. 2 displayed small energy dissipation, significant strength (\(\tau_{0}\)) and stiffness (G\({}_{0.33}\)) increments compared to non-rendered panels. Despite a very similar masonry typology, the structural response of the panels was very different. The predominant failure mode of rendered and non-rendered panels was in shear, which can be classified as a type of brittle tension failure with characteristic diagonal cracks along the diagonal in compression (Figure 10). Diagonal failure denoted tensile shear cracking at the center of the wall panel which afterwards began to behave as a rigid body, i.e., without further demolition of the wall specimen. The render did not detach from the masonry substrate during the test (Figure 10b). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Code**} & **Load-Capacity** & **Shear Strength \(\tau_{0}\)** & **G\({}_{0.33}\) (MPa)** & **G\({}_{u}\) (MPa)** & **Strain \(\gamma\) at** & **Residual Strength** \\  & **\(P_{\text{max}}\) (kN)** & **(MPa)** & **G\({}_{0.33}\) (MPa)** & **G\({}_{u}\) (MPa)** & **\(\tau_{0}\) (–)** & **at \(\gamma_{\text{max}}\) (MPa)** \\ \hline L-03-S & 58.81 & 0.0337 & 44.8 & 48.0 & 0.00221 & 0.0254 \\ L-04-B & 34.31 & 0.0317 & 248 & 38.8 & 0.00240 & 0.0263 \\ L-07-S* & 127.92 & 0.0813 & 940 & 317 & 0.000772 & 0.0514 \\ L-08-B* & 172.47 & 0.1655 & 1986 & 1329 & 0.000375 & 0.0257 \\ L-09-S & 43.55 & 0.0257 & 411 & 16.5 & 0.00494 & 0.0244 \\ L-10-S & 60.74 & 0.0363 & 75.9 & 8.31 & 0.01373 & 0.0356 \\ L-11-S & 39.02 & 0.0236 & n.a. & 8.44 & 0.00869 & 0.0233 \\ L-12-S & 61.71 & 0.0220 & n.a. & 9.24 & 0.00941 & 0.0217 \\ \hline \hline \end{tabular} \({}^{*}\) Rendered wall panels.  
\end{table} 
Table 4: Results of shear tests. Figure 9: Shear tests carried out on stone work panels cut off from Building No. 2 (rendered panels) and Nos. 3 and 4 (non-rendered). Values of the shear stiffness and residual strength are also reported in Table 4. The cement-based render seems to have an effect on the stiffness of the panels (G\({}_{0.33}\) and G\({}_{\rm u}\) values).