# Retrofitting Masonry Walls against Out-Of-Plane Loading with Timber Based Panels
## 1 Introduction  
Around the world, building stocks and urban infrastructures are ageing and require urgent action to extend their life. In the UK for example, less than 1-2% of total building stock each year are new build, while about 70% of the current building stock will still be in use in 2050. These statistics sustained the fact that retrofit of existing buildings and infrastructures will continue gaining increasing prominence over the coming years [1]. Most retrofits are driven by a combination of improving energy efficiency as well as enhancing structural capacity to damaged or vulnerable structures. In the case of historical structures, retrofitting is aimed at making buildings safer and less prone to major structural damage during an excessive loading to preserve their culture and heritage significances [2]. This desire to retain historical buildings that have cultural and heritage values are the motivation for this research on how to develop sustainable retrofit techniques for historical masonry structures. The prevailing rate of disasters such as damages and extensive loss of human lives that resulted from the collapse of old walls explained the vulnerabilities of older structures to extreme loading actions [3]. Since many of the old and historical structures are unreinforced masonry (URM) constructed long before the advent of the new seismic design codes, the retrofit of URMs against excessive loading actions is highly encouraged to avert substantial damages and loss of lives. In the case of historical masonry buildings, the problem is extremely complex because of the need for retrofitting to satisfy modern environmental standards and, of course, preserve the historical values. These special requirements arethe impetus for this study on how to develop sustainable retrofit techniques for historical masonry buildings. This research thus explored the possibilities of using timber as sustainable and economical material for the retrofit of masonry buildings. The priority is to improve the structural performance of masonry walls and minimise the risk of structural collapse and damages during out-of-plane loading. This study entails experimental and numerical investigation on the use of oriented strand board (OSB/type-3) timber panel in retrofitting unreinforced masonry walls. Over the years, several retrofit techniques have evolved to improve the capacities of masonry structures in resisting excessive out-of-plane loading, including earthquakes. The techniques can be broadly divided into two categories. 1. Member level: retrofit for particular members of the building such as walls, floor or roof [4]. 2. Structural level: retrofit aiming to improve the integrity and overall response of the whole building [4; 5]. Within each level of intervention, conventional and innovative techniques can be identified, as shown in Figure 1[6]. This study is on member level retrofit. The main benefit of member level retrofit in URM buildings is to bring the members to a condition that the members will be sufficient for the intended structural service [5]. The review of existing retrofit techniques carried out revealed that the potentials of timber have not been fully utilised in the structural retrofit of old masonry buildings. Timber is one of the oldest structural materials used in many parts of the world and known  
Figure 1: Classification of retrofit techniques. for its relatively higher strength to weight ratio [7] compared to concrete and mortar coatings, which are, instead, more often used for retrofitting URM walls. Timber also has high shear strength across the grains and good aesthetic quality, compared to FRP wrapping and steel bracing systems. Despite these obvious advantages and strength of timber, there is little evidence of using timber panels to retrofit old URM buildings. Indeed, timber panels are currently being used for energy retrofits such as insulation, vapour control and airtightness in old buildings [8].