DESIGN OF FRP RETROFITTED MASONRY UNDER OUT-OF-PLANE BENDING C.R. Willis 1 , M.C. Griffith 1 and J.M. Ingham 2 1 School of Civil, Environmental and Mining Engineering, The University of Adelaide, Australia. Email: cwillis@civeng.adelaide.edu.au 2 Department of Civil and Environmental Engineering, The University of Auckland, New Zealand. ABSTRACT The severity of damage possible in unreinforced brick masonry (hereafter termed ‘masonry’) construction subjected to high levels of out-of-plane loading has been well demonstrated in recent times. Due to the large global building stock of masonry structures, it is essential that efficient methods for retrofit of masonry structures be developed. The use of efficient fibre-reinforced polymer (FRP) strips has been shown to improve the load- carrying and displacement capacities of masonry sections subjected to out-of-plane loading. This paper presents principles for design of masonry elements strengthened with vertically oriented FRP strips and subjected to out- of-plane bending. Design considerations are given, along with recommendations based on experimental observations. Design variables discussed include retrofitting technique (i.e. externally bonded or near-surface mounted), FRP material (i.e. carbon or glass) and FRP placement (i.e. relative to mortar joints). A design methodology for masonry retrofitted with vertical FRP strips with intermediate crack (IC) debonding as the failure mode is also presented. KEYWORDS FRP, masonry, out-of-plane bending, strengthening, design. INTRODUCTION Background Inadequate out-of-plane bending strength of walls near the tops of buildings has been identified as of one of the governing weak links in the seismic load path for unreinforced brick masonry (hereafter termed ‘masonry’) buildings (e.g. Klopp and Griffith 1998). For this failure mode, the top storeys are generally critical due to the combination of increased earthquake induced accelerations (and therefore out-of-plane loading) with building height and reduced vertical compressive stress (e.g. Priestley 1985). This has been demonstrated in the analysis of structural damage after significant earthquake events, e.g. Whittier Narrows, California earthquake in 1987 (e.g. Deppe 1988; Moore et al. 1988). Recent catastrophic earthquake events in Italy (Pescaro, April 2009) and China (Sichuan, May 2008) have further demonstrated the severity of damage possible in masonry construction and again highlighted the need for retrofit of masonry structures. Efficient fibre-reinforced polymer (FRP) retrofitting technologies were initiated with reinforced concrete (RC) structures and have been adopted for use with masonry construction. Research (e.g. Oehlers and Seracino 2004) indicates that intermediate crack (IC) debonding is the most ductile, and therefore preferred, failure mechanism for FRP strengthened flexural members. The application of externally bonded (EB) and near-surface mounted (NSM) FRP reinforcement to the tension face of masonry sections under flexure has been shown to effectively increase the maximum strength and displacement capacity. This paper discusses key design considerations for FRP retrofitted modern clay brick masonry based on experimental observations (i.e. FRP retrofitting technique, material and placement). A design methodology for masonry retrofitted with vertical FRP strips with IC debonding as the design failure mode is presented. The methodology uses the generic IC debonding model developed by Seracino et al. (2007) for RC and subsequently modified for use with masonry by Yang (2006). 163