# Some Key Aspects in the Mechanics of Stress Transfer Between SRG and Masony
## 3 Discussion of Results
### Load Responses
#### 3.2.1 Influence of SRG Matrix Width  
For fourteen SRG-masonry joints, the width of the SRG matrix was equal to the width of the steel fiber sheet, i.e., 50 mm, and their behavior in terms of \(P\) versus \(g\) is shown in Figure 6a. The SRG matrix of the remaining blocks had two different widths: Figure 6b shows the results of SRG-masonry joints with matrix width equal to 70 mm, while Figure 6c shows the load response of specimens with the matrix width equal to 90 mm. The load responses were quite scattered even among specimens that belong to the same group, due to the variability of the mortar employed for the SRG matrix [35]. For low values of the load, the \(P\)-\(g\) curves were approximately linear. As the load increased, a series of load drops occurred, which were associated with the onset of the interfacial crack. For some specimens, after the initial drops, the global slip continued to increase at an almost constant value of the load (plateau). The value of \(g\) at the first substantial drop, which corresponds to the beginning of the plateau, is called \(g_{1}\), while the value of \(g\) at the end of the plateau is \(g_{2}\), which nominally corresponds to the end of the test. \(P_{crit}\) is defined in this paper as the average of the load in the interval \(g_{1}\)-\(g_{2}\), while \(P^{*}\) denoted the maximum load. The distinction between \(P^{*}\) and \(P_{crit}\) was first introduced to distinguish  
Figure 5: Failure modes of representative specimens: (**a**) interlaminar failure with debonding at the interface between the internal layer of mortar and steel fibers (MF); (**b**) partial interlaminar failure at the interface between the internal layer of mortar and steel fibers (MF*); (**c**) rupture of fibers (FR); (**d**) detachment of the SRG strip from the substrate with a thin layer of masonry attached to it (SF). between the load at the onset of the interfacial crack and the average load-carrying capacity of the joint during the propagation of the crack, respectively, in the case of steel-reinforced polymer (SRP) composites [47]. Since the energy required to create a unit-length crack is higher than that required for a unit-length self-similar increase in the crack, \(P^{*}\) was generally higher than the corresponding \(P_{crit}\) for the SRG-masonry joints that showed a plateau in the response. For twelve SRG-masonry joints, it was not possible to evaluate the \(P_{crit}\) since, after the first drop of the load, the response continued to increase until failure (see Table 3). Interestingly, for specimens with a matrix width equal to 70 mm and 90 mm, the always-increasing load response (i.e., the lack of a plateau) was associated with fiber rupture. On the other hand, when the matrix width was 50 mm, only one specimen out of four exhibited an always-increasing response that failed due to fiber rupture. This behavior was observed in [35]. The matrix-fiber bond is initially capable of sustaining loads almost close to the fiber rupture, and then a weakness at the matrix-fiber interface triggers the sudden interlaminar debonding. Most likely, the increase in the matrix width is capable of compensating for the presence of weaknesses at the matrix-fiber interface, and fiber rupture is often reached. The average of \(P_{crit}\) (\(\overline{P_{crit}}\)) for specimens with SRG matrix width equal to 70 mm (8.8 kN) increased by 52% with respect to the specimens with a matrix width of 50 mm (5.8 kN). Increasing the matrix width from 50 mm to 90 mm, \(\overline{P_{crit}}\) increased by 69% (9.8 kN). Therefore, increasing the matrix width for a constant fiber width entailed an increase in the load-carrying capacity of the SRG-masonry joint, due to a higher amount of energy required for the crack to initiate and propagate. Figure 6: Load responses of SRG-masonry joints with matrix width equal to: (**a**) 50 mm [35]; (**b**) 70 mm; and (**c**) 90 mm.