# Effect of Thin Cement-Based Renders on the Structural Response of Masonry Wall Panels
## 4 Results and Discussion  
### Results and Analysis of Compression Tests  
Four rectangular wall panels were tested for compression: two stone work and two brickwork panels. Table 2 shows the values of the maximum vertical forces recorded during the testing. The total number of the load cycles as well as maximum vertical displacement, Young's moduli, E\({}_{0.33}\) and E\({}_{u}\), and compressive strength, is given. Non-rendered wall panels were loaded until vertical cracks formed in the mortar joints, then loading continued and the compressive strength was determined. This typical failure mode is shown in Figure 7a. For the stone panel, a compressive strength of 0.796 MPa was found and, for the brickwork one, a value of 1.84 MPa could be calculated. Corresponding strain values were found to be 0.00158 and 0.00146, respectively. The deformation response of both stone and brick masonry walls was incrementally nonlinear and dependant upon the level of the compressive load. Table 2 also reports the test results for rendered wall panels. The failure mode of these panels was very similar to the one observed for non-rendered walls: the main difference was the progressive detachment of the cement-based render during the plastic non-linear phase of loading. Both the compressive strength and Young's modulus values did not significantly differ to those tested without the cement-based render. The maximum increment in strength was 16% for brickwork panels and this can be considered within the normal inherent variation for historic masonry. It should be noted here that the compressive strength \(\sigma_{0}=F_{\text{max}}/A_{0}\) was calculated by considering in \(A_{0}\) the cross sectional areas of both the render and panel. The limited effect of the render can be explained by considering the good mechanical properties of the masonry material in compression, not substantially different from those of the render. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Code**} & \multirow{2}{*}{\begin{tabular}{c} **Load-Capacity** \\ **\(F_{\text{max}}\) (kN)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **No. of** \\ **Cycles** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Compressive** \\ **Strength \(\sigma_{0}\) (MPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **E\({}_{\text{0.33}}\) (MPa)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **E\({}_{\text{a}}\) (MPa)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Strain at \(\sigma_{0}\) (\(-\))** \\ \(\sigma_{\text{r,pass}}\) (MPa) \\ \end{tabular} } \\ \hline C-01-S & 343.35 & 4 & 0.796 & 933 & 488 & 0.00158 & 0.792 \\ C-02-B & 496-77 & 6 & 1.84 & 1554 & 395 & 0.00451 & 1.81 \\ C-05-S\({}^{*}\) & 408.04 & 4 & 0.830 & 989 & 534 & 0.00146 & 0.781 \\ C-06-B\({}^{*}\) & 538.21 & 7 & 2.14 & 1888 & 488 & 0.00424 & 1.96 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of compression tests. Figure 7: Compression tests: (a) C-01-S; (b) C-06-B. Table 3 shows the default material properties of existing masonry obtained from the available Italian guideline [37]. By looking at the corresponding masonry category (Row 1: \"Irregular stone masonry\"; Row 6: \"Solid brick masonry with lime mortar\"), it can be noted that wall panels subjected to the compression test generally had ultimate strengths that are consistent with values suggested by the Italian guideline. A similar consideration can be made for the Young's modulus. The values found for stone masonry (933 and 989 MPa) and brickwork (1554 and 1888 MPa) fall into the range suggested by the Italian guideline (690-1050 MPa and 1200-1800 MPa) for the corresponding masonry typologies. The existence of a cement-based render seems to have little effect on the structural behavior of the wall, without affecting its load-capacity and deformation capacity. For these tests, a key-factor was the bond between the masonry substrate and the render. As cracking and debonding of the cement render occurred, the effect of the render became negligible.