ADVANCED COMPOSITE MATERIALS IN BRIDGES AND STRUCTURES MATÉRIAUX COMPOSITES D’AVANT-GARDE POUR PONTS ET CHARPENTES Calgary, Alberta, July 20 – 23, 2004 / 20 – 23 juillet 2004 1 A A A C C C M M M B B B S S S M M M C C C A A A P P P C C C I V IN-PLANE RESISTANCE OF URM WALLS WITH OPENINGS STRENGTHENED BY FRP COMPOSITES T. Li, N. Galati and A. Nanni Department of Civil, Architectural and Environmental Engineering University of Missouri-Rolla 1870 Miner Circle, Rolla, Missouri, U.S.A. tli@umr.edu galati@umr.edu nanni@umr.edu J.G. Tumialan Simpson Gumpertz & Heger Inc. 41 Seyon Street, Waltham, MA 02453, U.S.A. gtumialan@sgh.com ABSTRACT: In the recent years, on account of their excellent mechanical properties, fiber reinforced polymer (FRP) composites in the form of FRP laminates and bars have been widely investigated and proven to be an effective solution for the strengthening of unreinforced masonry (URM) walls. This paper describes an experimental program on the behavior of URM walls with openings representing windows and strengthened with glass FRP (GFRP) bars to improve the in-plane performance. This investigation intends to evaluate the influence of FRP reinforcement, placed horizontally and/or vertically, for improvement of the lateral load-carrying capacity, failure mechanism, ductility, and energy-dissipation capacity of URM walls with opening. Six full scale walls were subjected to in-plane cyclic loads using a racking test setup. The test results indicated that horizontal FRP reinforcement in the spandrel alone can not improve the structural performance of the wall. However, placing of vertical reinforcement in the piers can significantly increase the stiffness of the wall with mildly increase in the shear capacity of the wall. A combination of the aforementioned two strengthening scheme can significantly improve the load-carrying capacity and ductility of the wall. 1. INTRODUCTION Existing masonry buildings constitute a large portion of the building stock throughout the world. Many of these buildings are located in earthquake endangered regions and might contain structural components, for example, unreinforced masonry (URM) wall that do not meet requirements such as load-carrying capacity and ductility. Furthermore, walls are usually built with openings for doors and/or windows which significantly weaken their behaviour. Thus, there is an urgent need to investigate the ability of strengthening URM walls with openings to meet structural safety requirement and function requirement. In the field of rehabilitation and strengthening of existing masonry buildings, fiber reinforced polymer (FRP) have been increasingly used and have demonstrated to be very effective due to its outstanding combination of properties such as low-weight, immunity to corrosion, excellent mechanical strength and stiffness in the direction of the fibers, and capability of formation in very large dimensions. In the last decade, many researchers have investigated the effectiveness of this material in strengthening and retrofitting of concrete and masonry structures. Schwegler (1994) investigated the strengthening