# Retrofitting Masonry Walls against Out-Of-Plane Loading with Timber Based Panels
## 1 Introduction
Their application in structural retrofitting of URM walls, however, has still not been thoroughly studied. The experimental study by [PERSON] et al. [9] was the earliest on the application of timber panels as strengthening system for existing buildings against seismic force. The in-plane behaviour of URM retrofitted with cross laminated timber (CLT) panel was studied, and the results showed that there is a considerable increase in the strength and ductility of the retrofitted wall. That study [9] shows a 100% increase in ductility when the CLT panels are connected to URM walls with specially developed steel connections at the top and bottom of the wall. However, the availability of these unique connections in the open market is a concern limiting the applicability of the techniques. In addition, more recent research [10; 11; 12] explores the use of timber panels to retrofit masonry walls. Among them, experimental studies have been developed to evaluate the application of laminated veneer lumber (LVL) and CLT timber panels connected to masonry walls with screw anchor fasteners [10]. The study concludes that the proposed timber retrofit approach increases both the capacity and the stiffness of the retrofitted walls. Reference [11] proposed the combined use of CLT panels and steel cords to reinforce rubble stone masonry walls to increase the shear response of cracked stone masonry wall panels while also improving the energy performance of the building. The study [11] found that the proposed CLT and steel cords retrofit techniques enhanced the lateral capacity of retrofitted masonry wall panels by about 150%. Moreover, a study [12] proposed a masonry pier in-plane retrofit system consisting of an OSB panel connected to vertical timber strong-backs on masonry piers using anchor nails to increase the in-plane shear strength and stiffness of the masonry specimen. The study [12] shows an improvement of the seismic performance of the retrofitted wall, with an increase in ultimate displacement by 167% and its lateral strength by 35%. Earlier and recent studies [9; 10; 11] proposed the application of heavy CLT and laminated veneer lumber panels of thickness equal to 60 to 80 mm, which might be challenging to introduce in old URM buildings. In contrast, this study aims to propose the application of an 18 mm OSB type-3 panel to retrofit URM walls. OSB is regarded as a promising wood-based structural panel due to its superior strength, stiffness, workability and competitive pricing [13]. This research investigated the performance of OSB type-3 panels connected to URM wall by threaded dry rod connections and injectable chemical adhesive anchors readily available in the European market. The study proposed to investigate only the out-of-plane performance of the proposed techniques, because URM walls are more vulnerable when loaded in the out-of-plane direction and generate profuse damages upon failure. The advantages of this proposed retrofit technique include ease of application with low level of construction skills required, minimal cost compared to fibre-based application and no heavy additional load on the existing building due to the lightweight of OSB. It is also a reversible retrofit system and will prevent the total collapse of the building. It proffers a major increment in initial stiffness, strength and resistance of the retrofitted wall system. This paper presents the overall numerical investigation on the use of OSB/type-3 timber panel in retrofitting URM walls, calibrated and validated based on experimental tests. The paper is articulated into five main sections, including the introductory comments presented in Section 1. Section 2 presents the details of the materials and methods used in this study following the aim and objectives of the research. Section 3 includes the principal details of the experimental campaign from material characterisation, to small-scale test on masonry prisms, and large-scale tests on masonry walls.