# Out-of-Plane Experimental Study of Strengthening Slender Non-Structural Masonry Walls
## 3 Experimental Results Analysis with Discussion  
### Out-of-Plane Force-Displacement Response and Failure Mechanisms  
The rocking mechanism of as-built non-strengthened specimens develops after the cracking occurs at the top of the wall, which was closely followed by cracking at the bottom and mid-height of the wall, as a consequence of the exceeded masonry bond strength in bed joints along the whole specimen. With all three first specimens, NF-1, NF-2, and NF-3, the cracking pattern occurred at the first cycle of loading in a positive direction. The mid-height cracking as shown in Figure 5e appeared at bed joint heights of 208 cm, 193 cm, and 200 cm for the NF-1, NF-2, and NF-3 specimens, respectively (see Figure 5a-c). These values represent approximately two-thirds of the specimens' heights. Similar locations of mid-height cracks were obtained in separate experimental studies by other researchers [20, 62, 63]. With the increase in displacement amplitude, further crushing of the mortar in cracked bed joints was observed. A representative out-of-plane deformation shape of the as-built specimens is shown in Figure 5d. Figure 4: Applied general loading protocol for out-of-plane testing of non-structural wall specimens. Figure 5: Crack development locations (red dashed lines) of as-built specimens (**a**) NF-1, (**b**) NF-2, and (**c**) NF-3; (**d**) deformation shape of NF-1 and (**e**) mid-height crack opening of specimen NF-3. In specimens with applied full surface strengthening systems A and B (NF-A and NF-B specimens), multiple bed joint cracks were detected in the mid-height area with the constant bending moment. By covering the full surface of the specimen with the strengthening system on both sides, the precise determination of the exact location of the first crack at mid-height was prevented. The representative parabolic deformation line was observed in testing NF-A (see Figure 6a) and NF-B (see Figure 6b). After the cracking mechanism developed, the crushing of mortar in bed joints over the first and under the last row of units was observed in all strengthened specimens. When the displacement amplitude increased, reaching the maximum out-of-plane load-bearing resistance, the compressive failure of bricks in the first and the last rows was clearly observed in NF-A and NF-B specimens, as shown in Figure 6d. The complete failure of NF-A specimens was reached with the debonding of RF, as shown in Figure 6c. The typical failure of NF-B specimens occurred, as shown in Figure 6e, when the tensile strength of RM was exceeded along the whole width of the specimens. In the case of NF-1C and NF-1D specimens strengthened with diagonal and horizontal strips, the surface of the wall was not fully covered. Therefore, the formation of the first mid-height crack was possible to observe. The locations of first mid-height cracks were detected at the heights of 155 cm and 162 cm for NF-1C and NF-1D, respectively (see Figure 7a,b). After the development of cracking mechanisms, similar to NF-A and NF-B specimens, the crushing of mortar in bed joints over the first and under the last row of units was observed. The complete failure of the specimen NF-1D was reached after the tensile strength of diagonal RM strips was exceeded at the specimen's mid-height, at the diagonal RM strips' intersection (see Figure 7e). Hysteretic load-displacement responses for each specimen are presented in Figure 8, where mid-height displacement was measured with LVDT4 at the precise mid-height location. Cyclic tests were generally conducted up to the out-of-plane displacement amplitude where the near collapse state of the specimen was reached. Figure 6: Deformation shapes of full surface strengthened specimens (**a**) NF-A and (**b**) NF-B; characteristic failure modes: (**c**) debonding of RF in NF-2A, (**d**) compressive failure of bricks in NF-1A, and (**e**) tension failure of RM in NF-2B.