ABSTRACT
When reinforced concrete columns are subjected to seismic loading, the large lateral cyclic earthquake force will degrade the concrete and the reinforcing bar very quickly, and the columns will fail prematurely. Investigations of bridge failures during recent earthquakes, such as the 1987 Whittier, 1989 Loma Prieta, 1994 Northridge, and 1995 Kobe show that inadequate lateral reinforcement and insufficient lap length of the starter bars are among the major catastrophic causes of failure (Priestley & Whitter 1988; Buckle 1994; Priestley & Seible 1996; Parvin &Wang 2002). The main resisting system against earthquakes in many bridges is piers. In this kind of bridges all lateral force induced to bridge will be transferred to piers. Therefore any failure in this member results the overall collapse in bridge. In recent years, the use of externally bonded fiber-reinforced polymers (FRP) has been become increasingly popular for civil infrastructure applications, including wrapping of concrete columns. Significant research has been devoted to circular columns retrofitted with FRP and numerous models were proposed (Khaloo et al. 1991; Fardis & Khalili 1981; Miyaushi et al. 1997; Samman et al. 1998; Spoelstra et al. 1999). FRP wrapping of existing circular columns has proven to be an effective retrofitting technique (Seible et al. 1997; Chaallal et al. 2003). Retrofitting bridge columns is done because several reasons. One of these reasons is the lack of transverse reinforcing. In this case the shear
capacity of section is not sufficient for resisting against earthquake forces, transferred to the column fromdeck and other masses of bridge. On the other hand lacking of transverse reinforcing can cause decrease in deformation capacity in plastic hinges of bridges and it will lead to collapse of columns in plastic hinge regions. As mentioned before, for overcoming this deficiency, many engineers use FRP jacketing. FRP jacketing can increase strength of column and deformation capacity of it simultaneously. It has been shown that confinement with fiber reinforced polymer (FRP) improves the behavior of columns submitted to seismic loading (Priestley et al. 1992; Katsumata et al. 1987). FRP fabric wraps consisting of carbon, aramid, or glass fibers bonded by an epoxy resin have been successfully applied for seismic rehabilitation of bridge piers in the U.S. and Japan (Mufti et al. 1992; Kasei 1993). The growing use of FRP composites as confinement elements is attributed to the important mechanical and chemical properties of these materials. Some of these advantages are light weight, high-tensile strength and modulus, corrosion resistance, and durability. These advantages make FRP composites suitable for use in coastal and marine structures like river bridge piers. In additions, their low density is important because it adds less weight to the existing structures, and because the use of heavy equipment for repair with FRP composites is not necessary during rehabilitations. It has been shown that wrapping FRP fabrics around the perimeter of both circular and rectangular concrete columns to create a confinement effect
improves ductility and strength (Katsumata & Kimura 1990; Picher et al. 1996). Other FRP confinement techniques have been shown to improve the behavior of normal and high-strength concrete (Harmon et al. 1995). Retrofitting of concrete columns by lateral confinement with FRP wires has also resulted in an increase in strength and ductility under uniaxial compression (Nanni et al. 1994; Houssam & Toutanji 1999). Amount of lacking of transverse reinforcing is different in different case studies. In this research 4 samples with different amount of transverse reinforcing have been retrofitted by FRP jacketing method. The kind and thickness of FRP in all specimens are similar and the only difference between them is the amount of transverse reinforcing. In next part of this paper the properties of FRP is presented. After that specification of samples and analyzemethod have been explained. Finally the comparison between results has been done.
