Finite Element Modeling of Insulated FRP-Strengthened RC Beams Exposed to Fire J. G. Dai (cejgdai@polyu.edu.hk), W.Y. Gao & J.G. Teng Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong, China ABSTRACT This paper presents a finite element (FE) model for the thermo-mechanical analysis of insulated FRP-strengthened reinforced concrete (RC) beams exposed to fire. In the model, the effects of loading, thermal expansion of materials, and degradations in both the mechanical properties of materials and the bond behavior at FRP-to-concrete and steel-to-concrete interfaces due to elevated temperatures are all considered. The validity of the FE model is demonstrated through comparisons of FE predictions with results from existing standard fire tests on insulated FRP-strengthened RC beams. KEY WORDS 1 INTRODUCTION Despite its great success in the past two decades, the fiber reinforced polymer (FRP) strengthening technology suffers from one major limitation when indoor applications are considered. FRP composites show poor performance in fire as the polymer matrix typically has a low glass transition temperature, T g . The polymer transforms into a soft and viscous material with severe stiffness and strength degradations when it is subjected to temperatures close to T g . In addition, the polymer matrix may ignite under high heat fluxes, resulting in the generation of smoke and the spread of flames. Therefore, a layer of insulation material is often applied on the bonded FRP reinforcement to maintain the fire safety of the strengthened reinforced concrete (RC) member. A direct approach for evaluating the fire endurance of an RC member strengthened with FRP is to conduct a standard fire test. Limited standard fire tests (Bisby et al. 2005a; Gao et al. 2010; Williams et al. 2008) have indicated qualitatively that FRP-strengthened RC members with appropriate design and insulation can achieve satisfactory fire performance. However, such standard fire tests are usually very expensive and time-consuming and therefore, their usefulness is limited in providing a comprehensive, quantitative understanding of the fire performance of insulated FRP-strengthened RC members covering wide ranges of various design parameters. As an alternative to standard fire tests, numerical models for the fire resistance analysis of FRP-strengthened structural members have been developed. Bisby et al. (2005b) proposed a sectional model for the fire resistance analysis of FRP-confined RC columns. Hawileh et al. (2009) employed a nonlinear finite element (FE) model to study the heat transfer and deformation mechanisms in an insulated FRP-strengthened RC T-beam which was tested by Williams et al. (2008). In their work, both the external FRP and the internal reinforcing bars were assumed to be fully bonded with the concrete although bond failure between FRP and concrete is a common failure mode in FRP-strengthened RC beams. Indeed, the bond between FRP and concrete may degrade more rapidly than FRP itself under elevated temperatures. The fire endurance analysis of insulated FRP- strengthened RC members is more challenging than that of un-protected FRP-strengthened RC members as for the latter the contribution of FRP can be simply ignored [e.g. Han et al. (2006)]. Additional aspects that need to be considered in the former include the temperature- dependent behavior of FRP and interactions among FRP, concrete and steel reinforcement at elevated temperatures. This paper presents a generic and advanced FE model based on ABAQUS to simulate the thermal and structural responses of insulated FRP-strengthened RC members exposed to fire. 2 THE FE MODEL 2.1 Thermal and mechanical properties of steel, concrete and FRP at elevated temperatures The thermal conductivity, specific heat and thermal expansion of steel and concrete are defined following EN 1992-1-2 (2004). The thermal properties of carbon FRP sheets at elevated temperatures are determined according to Griffis et al. (1981) but the longitudinal thermal expansion coefficient of carbon FRP sheets is assumed to be zero based on ACI 440.2R-08 (2008). The uni-axial compressive stress-strain model for CICE 2010 - The 5th International Conference on FRP Composites in Civil Engineering September 27-29, 2010, Beijing, China L. Ye et al. (eds.), Advances in FRP Composites in Civil Engineering © Tsinghua University Press, Beijing and Springer-Verlag Berlin Heidelberg 2011