# Parametric Analyses of the Response of Masonry Walls with Reinforced Plaster
###### Abstract  
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. m 2022 20214 May 202214 May  
increasing their seismic performances are of the utmost importance, and a better understanding of masonry's behavior is fundamental to design these structures effectively. When local out-of-plane wall failures are prevented by appropriate connections between elements, the resisting mechanism that governs the global response of the structure is the in-plane shear capacity of the walls, which is directly associated with the masonry's shear strength. Among the different techniques commonly adopted to improve the in-plane performance of URM (see, for instance, [6; 7; 8; 9; 10; 11; 12; 13]), reinforced plaster (RP) is a widely used approach. It consists in placing a steel mesh on the wall surfaces and coating it with a layer of plaster, which can be made of concrete or a ready-mix mortar. In order to transfer the shear stresses on the wall across the concrete-masonry interface, appropriate anchors are fixed with a qualified mortar system (adhesive or cementitious grout) into pre-drilled holes made in the masonry wall and connected to the steel mesh. The method is easy to install, and it produces high increases in strength and stiffness. It is not surprising, therefore, that RP coating is one of the most common retrofitting interventions on masonry. Despite its frequent use, and even though many technical codes [14; 15] often suggest it as an effective retrofitting technique, it is difficult to obtain a satisfactory characterization of masonry with RP in the scientific literature, especially from an experimental point of view. To cover this lack of knowledge, an experimental study on masonry specimens retrofitted with RP is ongoing at Politecnico di Milano, with the aim of investigating the effectiveness of this strengthening solution. The diagonal compression test [16; 17; 18; 19], recommended by several national and international building codes to characterize the tensile strength of masonry, is being used as a tool to compare the responses of the analyzed specimens. In order to provide guidance to the experimental program, a numerical study was conducted on masonry walls, unreinforced and retrofitted with RP, analyzing the main parameters that have an influence on the in-plane structural response. Attention was given to several parameters, such as the mortar and plaster's properties, or the number of anchors.