# 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
In the case of non-strengthened as-built specimens (see Figure 8a-c), the test was terminated when the resistance of the walls dropped by 30% in comparison to its maximum value. From the hysteresis of as-built specimens, it was observed that the quality of workmanship has a significant impact on the out-of-plane behavior. Specim NF-1 had a properly filled bed joint over the first row: therefore, its hysteresis shows the highest out-of-plane resistance in both loading directions. In the case of specimen NF-2, the bed joint layer of mortar over the first row was incompletely filled on one side of the specimen, which led to the asymmetrical out-of-plane behavior. With specimen NF-3, the mortar layers in the bed joint over the first row were not fully filled with the mortar layer on both sides of the specimen. Since there was less mortar in the compression zone of the horizontal wall section in incompletely filled bed joints, lower out-of-plane resistance was achieved in a positive loading direction when testing specimen NF-2 and in both loading directions when testing specimen NF-3. Incompletely filled bed joints can be found in existing masonry structures, therefore, all of the as-built specimens were included in the analysis. Based on the force-displacement hysteresis analysis, the hysteretic loops can be separated into two groups, representing out-of-plane behavior for good (NF-good) and poor (NF-poor) workmanship. Whole hysteresis of the specimen NF-1 and the negative loops of the specimen NF-2 represent the out-of-plane behavior of walls built with good workmanship, while the positive loops of NF-2 and whole hysteresis of specimen NF-3 reflects the poor workmanship. After the development of plastic hinges, the out-of-plane resistance of NF-good specimens' loops reaches about 2.5-2.7 times higher values in comparison to NF-poor specimens' loops. This significant deviation between NF-good and NF-poor hysteretic response can be covered by the partial factor for materials according to the standard EN 1996-1-1 [64]. For the masonry units of category I and by using prescribed mortar by volume, the values of the factor are 1.7, 2.0, 2.2, 2.5, and 2.7 for classes 1, 2, 3, 4, and 5, respectively. The NF-good hysteretic loops obtained from the NF specimens are used as the control and serve as the basis for the strengthening systems' efficiency analysis. The out-of-plane resistances of the specimens strengthened with system A (NF-1A, NF-2A, and NF-3A) were similar, and the shapes of hysteresis were symmetric (see Figure 8d-f). The ultimate displacement was determined with the NF-2A specimen, where the instantaneous collapse occurred with debonding of the reinforcing glass fabric (RF) from the lower rows of the wall specimen (see Figure 6c). As it can be seen in Figure 8e, the out-of-plane resistance increased until failure. Figure 7: Crack development locations (red dashed lines) of specimens with diagonal and horizontal strips strengthening systems (**a**) NF-1C and (**b**) NF-1D; deformation shape of specimens (**c**) NF-1C and (**d**) NF-1D; (**e**) tension failure of RM diagonal strips at intersection in NF-1D. When testing strengthening system B, the complete collapse was achieved with the NF-2B and NF-3B specimens (see Figure 8g-i). As a characteristic failure for this type of strengthening system, a tearing of the rendering mesh occurred along the width of the specimen, which is a consequence of exceeded tensile strength of the rendering mesh (RM). Specimens NF-1B and NF-2B reach similar values of the maximum out-of-plane resistance, while the values in a positive direction for the specimen NF-3B are slightly lower. When testing the specimens NF-1C and NF-1D, a complete collapse of the specimens was not reached. After reaching its maximum value, the resistance gradually decreased down to approximately 30% of its maximum value (see Figure 8j,k).