## 3 The Experimental Campaign
### Investigated Parameters
#### 3.3.2 Crack Opening  
A crack in a masonry wall, either in the vicinity of an anchor or crossing it, is expected to affect the anchor behavior in a negative way. This is more so under seismic conditions, where the effect of cracking is combined with resistance and stiffness degradation due to repeated or cyclic loading. To assess the effect of cracking, several crack width values were investigated, namely, 0.30 mm, 0.50 mm, 0.80 mm, and 1.20 mm. Those tests have yielded the expected results regarding the negative effect of larger cracks on the behavior of anchors. However, the question arose as to whether a limiting value could be adopted for the crack width. It is noted that this is a parameter that also needs to be defined in the framework of the qualification of an anchor (compare qualification of fasteners in concrete, e.g., EAD 330499 [20]). Of course, such a limiting value should be related to the expected crack pattern of a masonry wall subjected either to in-plane or out-of-plane actions during a seismic event, to the reliability of such a prediction by the designer and--as a result--to  
Figure 3: Examined anchor locations: (**a**) in bricks; (**b**) in mortar joints; (**c**) index of adopted locations.  
the avoidance of the installation of anchors to regions where extensive and severe damage of the wall is expected to occur. Those issues are treated in [PERSON] et al. [21], based on the available literature related to tests on bearing masonry walls subjected to cyclic in-plane shear or out-of-plane bending. It is noted that, although numerous relevant tests are published, the authors of the respective works do focus on the crack pattern and its development, rather than on measuring the respective crack widths. Thus, the evaluation of the published results was in several cases qualitative. Nonetheless, the adoption of conceptually sound criteria has allowed for the deduction of a conservative, still realistic crack width value for testing anchors, within the research and qualification process. The two adopted criteria are the following: (a) The designer will avoid (following adequate guidelines) installing anchors in regions expected to undergo significant cracking or even disintegration during the design earthquake, e.g., the region along the diagonals of a wall subjected to in-plane shear. (b) Even if those vulnerable regions are avoided, one cannot exclude the occurrence of large cracks for large deformations imposed on the structural member bearing the anchors. However, it is reasonable to accept that the anchor reaches its maximum resistance simultaneously with the structural masonry element. In light of the qualitative and quantitative assessment of the experimental data, a crack width of 0.50 mm was adopted in most of the experiments presented herein. This is also the value recommended by the authors for use within an anchor qualification test program. Nevertheless, in this paper, the effects of crack widths other than 0.50 mm are presented and commented upon. Finally, (c) after the occurrence of oblique cracks to walls subjected to in-plane shear deformations, the vertical portions of the cracks (passing through vertical mortar joints) increase at a much higher rate than the horizontal portions of the oblique cracks. Nonetheless, it seems that one masonry unit away from the diagonal, even the opening of vertical cracks is not excessive [21]. However, due to the limited relevant quantitative experimental data, and considering the lower quality of vertical mortar joints, it may be wise to encourage the designers to avoid as much as possible the installation of anchors in vertical mortar joints.