Fire behaviour of FRP-strengthened reinforced concrete structural elements: A state-of-the-art review

Abstract

The last two decades have seen increasing applications of fibre reinforced polymer (FRP) materials in civil engineering structures due to their many advantages over traditional strengthening and reinforcing materials. Among the most common applications is bonding or wrapping FRP products (strips or sheets) to the exterior of reinforced concrete (RC) members to increase their strength or deformability. However, widespread application of FRP strengthening systems in buildings, where structural fire ratings are required, is hindered due to unknowns surrounding the reduction in their mechanical and bond properties at elevated temperatures. This paper presents a state-of-the-art review on the fire performance of FRP-strengthened RC structural elements. The review addresses first the mechanical behaviour at high temperature of the constituent materials of FRPs and how their bond to concrete is affected when heated. The paper then discusses available experimental and numerical studies on the fire behaviour of FRP-strengthened RC beams, slabs, and columns. Available design guidance is also discussed. Finally, recommendations for future research are given.

Introduction

Beginning in the 1980s and experiencing an acceleration of research interest in the 1990s that has continued until present day, applications of fibre reinforced polymer (FRP) materials in civil engineering structures are now widespread. Among the most common applications of FRPs in structural engineering is bonding or wrapping FRP products (strips or sheets) to the exterior of reinforced concrete (RC) members to increase their strength, stiffness, and/or deformability. From early on in the development of FRP strengthening systems for RC elements, attempts to apply FRPs in buildings have been hindered due to concerns and unknowns surrounding the reduction in their mechanical and bond properties at elevated temperatures. Considerable research has therefore been undertaken in an attempt to better understand the response of FRP materials and FRP strengthened RC elements at high temperatures or in fire. A review of the then state-of-the-art in this area was presented by Bisby et al. [1] in 2005, now a decade ago.

This paper presents a timely state-of-the-art review on the fire performance of FRP materials and FRP-strengthened RC structural elements. It begins by discussing available research on the performance of FRP constituents and materials at elevated temperatures (including fibres, resins, and composites). The focus is on tensile and bond properties, since these are the most important in RC strengthening applications. Analytical models to predict FRP property reductions and to correlate mechanical and bond properties to glass transitioning of the resins and adhesives are presented and discussed. Possible advantages of near surface mounted (NSM) FRP strengthening systems, as compared with externally-bonded reinforcement (EBR) systems, are reviewed with a focus on bond performance at high temperature. The available fire resistance tests on FRP strengthened RC elements, including columns, slabs, and beams are reviewed and discussed, as are the available modelling studies which have attempted to predict the fire resistance and mechanical response of FRP strengthened RC elements at elevated temperatures. Finally, international guidance for structural fire resistance design of FRP strengthened concrete elements is summarized, and recommendations for future research in this area are suggested.