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Fire and high temperature influence properties (strength, stiffness, young’s modulus) of FRPs extensively. It is necessary to understand the influence of high temperature and fire in order to consider proper fire protection strategy. Fire performance of FRPs are as crucial in design considerations as modulus of elasticity and yield stress.The maximum temperature of FRP is controlled by glass transition temperature and temperature at which chemical decomposition starts to become significant.

The maximum temperature of FRP is controlled by glass transition temperature and temperature at which chemical decomposition starts to become significant.

In order make FRPs fire resistant, it is required to use fire retardant admixture and regular gelcoat in the construction of FRPs. The fire-retardant agent would improve fire resistant of the FRP and the gelcoat prevent environmental defects that may FRPs suffered due to the presence of fire-retardant agent in its composition.

The use of externally-bonded FRP plates and sheets to strengthen existing reinforced concrete structures is now widely recognized. However, a primary concern that still discourages the use of FRPs in some cases is their assumed susceptibility to fire. Finally, it is shown that the overall performance of appropriately designed and insulated FRP-strengthened reinforced concrete members is satisfactory.

Effect of Fire and High Temperature on FRPs

1. Strength and Stiffness of FRPs

Both strength and stiffness of FRPs would be reduced if it exposed to elevated temperature. It is demonstrated that, Carbon FRP is insensitive to high temperature, but the strength and stiffness of the composite decreases at temperature of higher than 200C.

Tensile strength and modulus of elasticity of CFRP, GFRP, and AFRP decrease 10, 20, and 30%, respectively when they are exposed to service temperature of up to 60C.

Tensile Strength Reduction of FRP with Rise in Temperature
Fig. 1: Tensile Strength Reduction of FRP with Rise in Temperature

2. Bond Properties of FRPs

The bond characteristics of FRPs is substantially declined at a temperature higher than glass transition temperature. The bond of FRPs is dependent on the shear properties of the matrix or the adhesive.

3. Fire Spread, Smoke Generation, Toxicity

Thermoset resin, which is widely used in the structural FRPs, have fairly poor flame spread characteristics but produce intolerable quantities of smoke. The application of coating or barrier treatment can significantly enhances ignition and fire spread of FRPs.

4. Fire Resistant of FRP-reinforced Concrete Members

The fire resistant of concrete members reinforced with FRPs is similar to that reinforced with steel but greater cover is needed to keep temperature of FRPs under acceptable limits. Thermal insulation should be applied for structural elements reinforced with externally bonded FRPs in order for the FRPs show satisfactory fire resistant.

It takes 1-hour fire exposure for a well-insulated externally bonded concrete elements to lose its bond. Nonetheless, a fire rating of 4 hours has been achieved by considering proper design, construction, and fire-resistant techniques.

The steel plates debonded from the beam in 8 minutes. The carbon FRP began to burn at the surface of the laminates and their cross sections slowly decreased. The carbon FRP debonded from the beam after one hour.

About Madeh Izat HamakareemVerified

Madeh is a Structural Engineer who works as Assistant Lecturer in Koya University. He is the author, editor and partner at theconstructor.org.