# Tensile Capacity of Adhesive Anchors in Damaged Masonry
## 1 Introduction  
It is well-known that masonry structures are highly vulnerable to seismic actions, since they have great mass, low tensile strength, and ductility. In addition, in many cases the geometrical and/or mechanical irregularities increase the vulnerability of masonry structures [1, 2]. In the past decades, many efforts have been made to assess the vulnerability of existing structures by developing assessment techniques [1, 2, 3, 4, 5, 6, 7, 8] and to evaluate the effect of the different strengthening techniques by performing experimental research [9, 10, 11, 12]. It is well-known that the improvement of the \"box like effect\" could be achieved in several ways, but one very common technique is the use of steel connections [11, 12]. Among them, post-installed anchors are very popular, because of their flexibility and easiness of installation. In addition, in Europe the qualification and design of post-installed injection anchors for use in masonry are regulated according to EOTA provisions [13, 14] and thus the reliability of the application is guaranteed. Nevertheless, the existing approach--being developed for static and quasi-static actions--only considers the assessment of performances in uncracked masonry, while it is well-known that, especially under seismic events, masonry develops a more or less diffused crack pattern [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]. The assessment of post-installed bonded anchors in concrete [16] clearly distinguishes between non-cracked/cracked concrete and, depending on different parameters (type of adhesive, bar diameter; crack width...) the reduction of load, between the two conditions (non-cracked/cracked) could easily reach 50%. The designers of reinforced concrete(RC) structures must distinguish, on the basis of structure characteristics, between non-cracked/cracked condition, and avoid installing anchors in critical areas (e.g., plastic hinges) [17]. For anchor applications in concrete under seismic actions, the base material is always assumed to be cracked. As the current concept for masonry anchors only considers predominantly static and quasi-static actions on the anchors and thus implies the same conditions for the masonry structures, there is no distinction in the assessment between cracked and non-cracked masonry, and qualification testing is performed in the non-cracked condition [13]. Uncertainties coming from e.g., cracking, are regarded to be covered in the design by a higher partial safety factor for the base material vs. concrete [14]. Furthermore, as additional parameter for the anchor resistance the concept considers its position within the masonry (e.g., in a mortar joint, in the brick, close to the edge... ). Basic investigations under quasi-static loading are reported in [18; 19; 20], but due to the complexity of masonry injection anchor performance assessment is still mainly based on experimental testing [13] and only few predictive equations are used in design [14]. In the past decades, many efforts have been made to evaluate the behavior of post-installed anchors in concrete [21; 22; 23; 24; 25; 26; 27; 28; 29; 30] under different conditions (i.e., concrete strength, cracked/non cracked), leading to a well-defined standard framework that allows designers to rely on equations or testing procedures that consider the determination of the performance of a fastener even under critical conditions such as seismic action. Recently, some researchers paid attention to the behavior of anchors in masonry or stone [11; 18; 19; 20; 31; 32; 33; 34; 35; 36; 37], but some specific aspects such as the behavior in real structures under seismic influences including damaged and cracked masonry, to the knowledge of authors, are still not investigated [33]. Ref. [20] reports a mean resistance reduction due to cracking of up to 70% for shallow injection anchors installed in solid clay or calcium silicate single bricks and tested under monotonic tension loading and adverse conditions.