Fire resistance of RC and FRP-confined RC columns

The retrofit of columns by fibre-reinforced polymer (FRP) confinement has become a popular technique over the past decade but when this technique is adopted to strengthen reinforced concrete (RC) columns in buildings, the fire resistance of the strengthened column is often a serious design concern. This paper addresses the issue of assessing the fire endurance of FRP-strengthened RC columns. Since the FRP jacket loses its strength rapidly in a fire, the mechanical resistance of the FRP composite is ignored in this study, and instead attention is focused on the ability of the original RC column in resisting the design loads for the fire limit state. The paper first presents a theoretical model for the deformation and strength of RC columns in fire, which, in conjunction with a finite element method for the temperature field analysis of RC columns, can be used to predict the fire resistance of RC columns and FRP-confined RC columns with or without fire protection, Comparisons of results predicted using this model with test results show close agreement in general. The paper also presents the results of a parametric study to examine the effects on the fire endurance of RC columns of the following parameters: material strengths, section size, steel reinforcement ratio, load eccentricity ratio, depth-to-width ratio and slenderness ratio. Based on these results, a design proposal for evaluating the fire resistance of RC columns is presented. Finally, the application of this design proposal in afire resistance assessment of an FRP-confined RC column is illustrated.