ABSTRACT
The superior mechanical properties of the fiber reinforced polymer (FRP) composite material led to the fast development of research of FRP materials (Teng et al. 2002, Sundarraja et al. 2012). The advantages and disadvantages of using one kind of FRP materials, such as carbon fiber reinforced polymer (CFRP) glass fiber reinforced polymer (GFRP), or basaltic fiber reinforced polymer (BFRP) to strengthen concrete columns are obvious (Guo et al. 2009). Recently, research work about FRP strengthening method is focused on hybrid strengthening program (Chen et al. 2008, Li et al. 2009, Mosallam et al. 2012), and obtain FRP confined new members (Guo et al. 2009). The study on hybrid fiber reinforced polymer (HFRP) to confine concrete members had been mainly focused on HFRP reinforced concrete beams and columns (Li et al. 2009, Chen et al. 2012, Lau and Pam 2010, Rousakis et al. 2012). To study the behavior of HFRP reinforced concrete structures, the fundamental step is to understand the basic mechanical behavior of the constitutive materials, reinforced concrete and FRP, separately. The nonlinear behavior of reinforced concrete such as concrete cracking, tension stiffening, shear retention, concrete plasticity and yielding of reinforcing fiber have been extensively studied by many researchers and numerous proper constitutive laws have been proposed (Hu et al. 1989). However, the studied on mechanics of HFRP confined concrete structures especially columns is limited. While, the stress-strain relation of HFRP confined concrete columns is necessary in design of structures especially for aseismic design of structures. Different stressstrain models of FRP confined concrete materials were presented by Miyauchi et al. (1999) and Samaan
et al. (1998), however the most common one is the model presented by Teng et al. (2002), which had been accepted by most of the researches so far, but the model is still too completed to be used to engineering design easily. Therefore, appropriate modeling of the nonlinear behavior of HFRP confined concrete is still crucial.
