Twisted steel bars are often used to strengthen masonry buildings and, in particular, to improve the transverse connection between different structural elements. The performance of the retrofitted structure depends on several parameters such as the mechanical properties of the base material (masonry), the bar diameter, the pre-drilled hole diameter. The paper presents the numerical assessment of the tensile behavior of twisted stainless-steel bars installed in brickwork masonry. Nonlinear numerical models in Abaqus software were developed and validated on the basis of experimental results, considering different bar diameters (8, 10, 12 mm). A parametric study was conducted to examine the factors that could influence the performance, namely the embedment depth, the pre-hole diameter, and the mechanical properties of the base material. The outcomes reveal the sensitivity of the twisted bars to the aforementioned parameters. In particular, the twisted bars exhibited a higher capacity in stiffer base materials, with longer embedment and smaller pre-drilled hole. However, none of the above parameters proportionally affect the ultimate strength, but lead to a limited improvement in the ultimate capacity (up to 40% in the considered range).

Steel reinforced plasters (SRP) are a traditional strengthening solution of existing masonry structures. SRPs consist of a thin layer of cementitious mortar or concrete (jacket) that incorporates a steel reinforcing mesh tied to a series of steel bent connectors embedded in the underlying masonry. Despite the recent development of more innovative retrofitting methods, SRPs are still widely adopted because of their low costs and effectiveness in terms of improved performance. In the present paper, a comprehensive experimental program on brickwork masonry walls is presented. The results are intended as a contribution to the knowledge of in-plane behavior of masonry strengthened with SRPs. Unreinforced and plastered masonry walls were subjected to cyclic diagonal compression loading under displacement control. Different thicknesses of walls (2 and 3 wythes) and plasters (30 and 50 mm) were selected. The performances of the plastered and non-plastered specimens were analyzed and compared. The results showed that the SRPs increased considerably the performance of the walls in terms of both strength and deformation capacity. The plaster's thickness had limited effects on the load carrying capacity of the walls, whereas it had a significant effect on their ductility. Finally, the connectors used to tie the steel mesh to the masonry walls played an essential role and avoided large out-of-plane displacements of the plaster layer after its detachment, thus preventing instability phenomena.

This paper presents the results of a parametric study on the response of unreinforced and retrofitted masonry specimens. The adopted strengthening technique is the steel-reinforced plaster, which is very commonly used but it is not supported by a proper theoretical and experimental characterization in the scientific literature. The aim was to investigate the main parameters that affect the structural performances of the walls. Several numerical models were implemented using the finite element method to analyze the influence of the bricks’ arrangements, the mechanical properties of the mortar joints, the number of connectors, and the mechanical properties and thickness of the plaster coating. A concrete damage plasticity model was adopted to describe the bricks, the mortar joints, and the plaster behaviors. For the unreinforced specimens, the outcomes confirmed that the mortar strength had a significant influence on the performance of the wall, together with the presence of potential weaknesses in the bricks, while the bond effect was negligible. For reinforced walls, the connectors do not have a significant influence on retrofitted wall capacity but may prevent instability if a proper number is considered. Furthermore, the strength of the plaster coating does not affect the collapse load significantly, while increasing the fracture energy, which can be produced, for instance, by using fiber-reinforced concrete, increases the capacity of retrofitted walls, with more limited damage. Finally, an increase in the plaster thickness may be beneficial in terms of collapse load, even though greater thickness may increase the seismic masses significantly.

In Europe, the qualification of injection anchors in masonry under static and quasi-static actions is based on an assessment of tests performed in undamaged masonry. Nevertheless, in seismic prone countries like Italy the influences deriving from earthquake actions cannot be disregarded. Masonry elements are very sensitive to cyclic/seismic action and research on the behavior of anchors in damaged masonry is rather limited. The paper presents the results of an experimental campaign aimed at evaluating the residual tensile strength of adhesive anchors installed into undamaged walls that were subsequently subjected to cyclic in-plane loading to simulate seismic actions before. Consequently, the anchors experienced different stresses depending on their location within the walls. Overall, 29 tests were performed with anchors placed both, in undamaged and damaged areas. The results showed that there is a correlation between residual tensile strength and masonry initial conditions, and therefore the installation of anchors in masonry elements should be carefully planned avoiding areas that could be heavily damaged during seismic events or considering redundant connections in critical areas. In particular, it seems that the width of the crack (created by cyclic actions) that passes nearby/into the anchor borehole is the main parameter that affects the ultimate resistance of the anchors.