Mechanical characterization tests and numerical simulations for evaluating the effectiveness of fibre- reinforced cementitious mortar as shear strengthening of masonry walls

The use of fibre-reinforced mortars (FRM) has been developing for the strengthening of masonry panels as an alternative to traditional reinforced plaster; despite this, analytical formulations to quantify the effect of such systems have not yet been released. This work evaluates the effectiveness of an FRM system composed of polyvinyl alcohol fibres in shear strengthening of masonry panels. An experimental campaign was carried out to characterize the mechanical properties of the materials and the adhesion between the coating and different masonry supports. Based on experimental results, a finite element model was developed to investigate the effectiveness of the strengthening system. The results show that the application of fibre-reinforced mortar leads to a significant in-plane shear strength increase and a comparison with current code provisions for traditional reinforced plaster was carried out. A new analytical formulation was developed to quantify the shear strength of reinforced panels. 1 Introduction Preserving the architectural heritage is a major challenge in the construction field. Recent seismic events have highlighted the significant vulnerability of older buildings, particularly masonry structures, to earthquake damage. Several systems have been developed to improve the structural response of masonry buildings using traditional (i.e., reinforced plaster) or innovative inorganic-matrix composites externally bonded to wall surfaces. Among them, in last years, Composite Reinforced Mortar (CRM) and Fibre-Reinforced Ce-mentitious Matrix (FRCM) systems have been widely investigated and used [1], [2], [3]. All these systems, whether traditional or innovative, involve the application of a mortar layer to the outer faces of the masonry, reinforced with a steel or a composite grid embedded in the coating. A novel alternative is presented by the Fiber Reinforced Mortars (FRM): in this strengthening system, no mesh is applied; instead, short fibres are randomly dispersed within the mortar, ensuring good tensile response and high ductility counteracting the progressive opening of cracks. Fiber-reinforced concrete is well known in literature and widely used as a construction material, and in this field specific qualification and design guidelines are already available [4], [5]. Conversely, the application of this system for strengthening existing masonry structures has not still been deeply explored, and only in recent years some studies have been carried out to investigate the in-plane [6], [7] and out-of-plane strengthening of masonry walls [8]. Moreover, no specific analytical formulation is currently available to quantify the effect of FRM reinforcement in terms of masonry strength increase, and only a few studies have been conducted in last years to address this gap [9]. In this work, an experimental campaign and a parametric numerical analysis were carried out to assess and quantify the effect of an FRM system, composed of a cementitious mortar and polyvinyl alcohol fibres, in the in-plane shear strengthening of masonry walls. Three different masonry typologies have been analysed: solid brick, hollow brick and stone masonry. The results show that the application of the FRM system leads to a significant shear strength increase. The comparison with the amplification coefficient of strength proposed by current Italian code for traditional reinforced plaster was carried out, highlighting that such coefficient can also be suitable for application to FRM systems. Finally, a new analytical procedure was developed to assess the in-plane shear strength of reinforced panels.