## 2 Experimental Program
### Shear Strength Test  
Six masonry prisms of SCMU assemblages (denoted by PS1-PS6), as presented in Table 3, were prepared according to the procedure specified by the Chinese Masonry Code for shear strength test [17]. The masonry prism of shear test was 390 mm in length, 240 mm in width, and 590 mm in height, as shown in Figure 6. The shear prisms were constructed with three courses in running bond pattern. All shear prisms were cured in the standard conditions (22 \(\pm\) 3 \({}^{\circ}\)C and 95% RH) for 28 days. Before testing, the prisms were capped with a 10 mm thick cement mortar to have a uniform bearing surface.  
Shear strength test was performed using two load cells. One load cell (Shanghai Huali Sensor Technology Co., Ltd., Shanghai, China) was used to apply a constant vertical precompression load while the second load cell (Shanghai Huali Sensor Technology Co., Ltd., Shanghai, China) was used to apply an increasing horizontal load. Steel plates were installed to ensure a uniform distribution of load and to control the location of supporting points.  
Prisms PS1, PS2, and PS3 were tested under precompression of 0.1 N/mm\({}^{2}\), whereas prisms PS4, PS5, and PS6 were tested under precompression of 0.3 N/mm\({}^{2}\). Then the pressures were kept constant while the shear load was applied until the failure of the prism occurred [21,22]. Shear load was increased at a rate of 0.1 N/mm\({}^{2}\) per minute.  
Four potentiometers (Liyang Instruments Co., Ltd., Liyang, China) (i.e., two at each side) were placed to monitor the slip between the outer and middle units. All measuring devices were connected to a computer (ASUSTeK(r) Computer Inc., Taibei, China), which processed the data in real time. Figure 7 shows the shear strength test setup.  
Figure 5: Typical failure mode of prism.  
Figure 6: Masonry prism for shear test (units in mm).  
Table 3 shows the results of shear strength test. The influence of the applied level of the pre-compression is clearly visible from Table 3. The results revealed that the shear resistance increases when increasing the level of pre-compression. The failure occurred at the bed joint for all specimens, as shown in Figure 8. The failure patterns observed during the tests can be characterized as sliding failure mode. Sliding failure of the prism can be described by the classical [PERSON]'s failure criterion equation:  
\[\tau=c+\sigma\mu\phi \tag{1}\]  
where, \(c\) denotes the cohesion, \(\phi\) is the angle of internal friction, \(\sigma\) is the normal stress.  
Based on the test results presented in Table 3, the friction coefficient in the bed joint can be calculated based on the levels of compression and shear in the joint once sliding has occurred [22]. The resulting shear-stress-normal-stress graph is shown in Figure 9, which has been obtained from a linear regression of points. The average cohesion and friction angle in the bed joints of the SCMU prisms are, respectively, 0.5433 N/mm\({}^{2}\) and 33.7\({}^{\circ}\).  
Figure 8: Typical mode of failure for masonry shear prism.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Specimen No.** & **Precompression Load**\(F_{\text{pl}}\) **(kN)** & **Maximum Shear Load**\(F_{\text{max}}\) **(kN)** & **Precompression Stress**\(\sigma_{i}\) **(N/mm\({}^{2}\))** & **Shear Stress**\(\tau_{i}\) **(N/mm\({}^{2}\))** \\ \hline PS1 & 8.7 & 103.0 & 0.10 & 0.60 \\ PS2 & 8.5 & 106.7 & 0.10 & 0.62 \\ PS3 & 8.4 & 105.1 & 0.10 & 0.61 \\ PS4 & 26.0 & 126.8 & 0.30 & 0.74 \\ PS5 & 25.0 & 124.5 & 0.29 & 0.73 \\ PS6 & 27.0 & 130.3 & 0.31 & 0.76 \\ \hline \end{tabular}
\end{table}
Table 3: Shear strength results of masonry prisms.  
Figure 7: Shear test general setup.