Three-Level Fire Resistance Design of FRP-Strengthened RC Beams

Abstract

The use of externally bonded fiber-reinforced polymer (FRP) systems in the strengthening of reinforced concrete (RC) members has become widely accepted in recent years. A significant concern with this technique is the fire resistance of the strengthened member, for which a systematic design procedure that can be easily implemented by practicing engineers is not yet available. This paper for the first time presents such a procedure for the fire resistance design of FRP-strengthened RC beams. The proposed procedure distinguishes three levels (Level I, Level II, and Level III) of fire insulation design to satisfy the specified fire resistance rating. In Level-I design, no fire insulation is provided and the FRP system is completely ignored; the RC beam itself is expected to survive the required fire resistance period. At the other extreme is Level-III design, in which the FRP system and the original RC beam need to be so insulated that they both remain effective during the required fire resistance period. Between the two extremes is Level-II design, in which a moderate level of fire insulation is provided to protect the RC beam rather than the FRP system. Level-I and Level-III design can be realized using appropriate methods proposed by the authors in previous studies. For Level-II design, a simple design method based on the so-called 5°C isotherm method is presented and assessed using numerical data generated by finite-element (FE) analyses. Although the present paper is concerned only with FRP-strengthened RC beams governed by flexural failure, the general framework presented can be readily extended to other FRP-strengthened RC components as well as FRP-strengthened RC structural systems.