Fire Resistance of FRP Reinforced Concrete Beams

1. Fire Resistance of FRP Reinforced Concrete Beams Presented By: Abu Naim Md Rafi Student ID: 103149637 December 6, 2010 Department of Civil and Environmental Engineering University of Windsor

2. Outline • Research Objectives • Fire Performance of Concrete • Fire Performance of FRP • Fire performance of FRP reinforced Beam • Experimental Study • Analytical Work • Conclusion

3. Research Objectives • To perform a review of the existing literature regarding the performance of FRP reinforced concrete beams at elevated temperature • Understand the performance of FRP reinforced beams at elevated temperature based on the results published in the literature

4. Fire Performance of Concrete • Internal stresses increased by • Evaporation of free moistures • Dehydration of CSH • Thermal expansion of aggregate • Excessive increase in internal • pressure results spalling • Strength and stiffness reduces • significantly due to exposure Figure : Concrete Strength Reduction Factor with Temperature (This figure is produced from the value presented by Wang et al. (2009) based on Eurocode 2)

5. Fire Performance of FRP • High temperature behaviour of FRP is different than the high temperature behaviour of steel and concrete • It is well established that material properties of FRPs deteriorate with increasing temperature • Fibres are relatively more resistant to thermal effect so degradation of mechanical properties are governed by properties of polymer matrix • The critical temperature is commonly taken to be the glass transition temperature of the polymer matrix • Typical range of is between 65-120˚C for matrix used for infrastructure application

6. Fire Performance of FRP • Due to anisotropy ,transverse properties are more affected by elevated temperature and the transverse strength and stiffness decreases rapidly above glass transition temperature • When used as a reinforcement the most important properties of FRP influencing structural behaviour at elevated temperature are • Strength • Stiffness and • Bond properties with the concrete

7. Fire Performance of FRP Strength Figure : Variation of Tensile Strength of FRP with Temperature (This figure is produced from best fit sigmoid curves presented by Bisby et al. (2005) based on data presented in the literature.)

8. Fire Performance of FRP Stiffness GFRP and AFRP CFRP Figure : Variation of Stiffness of FRP with Temperature (This figure is produced from equations presented by Saafi (2002) based on experimental results collected by Blontrock et al. (1999))

9. Fire Performance of FRP Comparison with steel AFRP and GFRP CFRP Steel Figure : Comparison of Strength and Stiffness of FRP with Steel at Elevated Temperature (Strength and stiffness of steel are according to CSA S16 (2009))

10. Fire Performance of FRP Bond properties with concrete • Katz et al. (1999) performed experimental study to evaluate bond strength of FRP and steel with concrete at elevated temperature • A reduction of between 80 and 90% in the bond strength was observed as the temperature is increased from 20˚C to 250˚C. • Ordinary deformed steel rebars showed a reduction of only 38% in the same temperature range.

11. FRP Reinforced Beams in Fire • The research work performed to understand the behavior of FRP reinforced concrete beams at elevated temperature can be divided into two groups • Experimental work • Analytical Work • Abbasi and Hogg (2005) • Rafi et al. (2007) • Rafi and Nadjai (2008) • Saafi (2002) • Abbasi and Hogg (2005)

12. Experimental Study Figure : ISO 834 Standard Time-Temperature Curve (1980)

13. Experimental Study Abbasi and Hogg (2005) • Tested three RC beams • 350 x 400mm cross section • Compressive strength of concrete was 42 MPa (100mm cube) • Six point bending test

14. Experimental Study Abbasi and Hogg (2005) • The control specimen tested at room temperature • Load-deflection become non-linear after an applied load of 60 kN • For fire test 40 kN load was applied and subjected to standard fire • Subjected to heating on three sides • Early Failure of beam 2 is due to weaker bond strength • Clear cover of 70 mm recommended Figure: Heating time-deflection curve (Abbasi and Hogg, (2005))

15. Experimental Study Rafi and Nadjai (2008) • Tested seven RC beam • Cross section 120 x200mm, 20mm concrete cover • Four point bending test • 40.60 MPa concrete cylindrical strength • Three beams reinforced with steel (D=10mm ,strength =530MPa, E=201GPa) • Four beams reinforced with CFRP (D=9.5mm, strength=1676 Mpa, E=135.9 Gpa) • Shear reinforcement was steel (D=6mm, strength=421 MPa, E=200GPa) • Two steel RC beam and two FRP RC beam tested at room temperature until failure • 1 steel RC beam and 2 FRP RC beam were subjected to service load (35% of ultimate load) and then tested under standard fire

16. Experimental Study Rafi and Nadjai (2008) • At ambient temperature the cracked FRP reinforced concrete beams deflected more than the steel RC beams • After yielding of the steel the rate of deflection of the steel beams were greater than that in the FRP beams • At both elevated and ambient temperature steel RC beams failed by steel yielding and the FRP RC beams failed by concrete crushing • FRP RC beams were stiffer than steel RC beam at elevated temperature • Failure of steel beam occurred at 79 minute • Failure of two CFRP beams occurred around 50 minute and 60 minute • The FRP rods at one end of beam slipped close to their failure

17. Analytical Work Saafi (2002) • Presented a simple analytical study of the fire performance of FRP reinforced concrete beams • Based on the FRP and concrete properties at elevated temperature and the contours developed in side the beam, the residual flexural and shear capacity has estimated • Flexural and shear capacity at elevated temperature has calculated by ACI Committee 440 equations • For calculating the temperature contour inside the beam he has used the model proposed by Desai (1998)

18. Analytical Work Saafi (2002) Figure : Temperature in FRP Reinforcement (Saafi (2002)) Figure : Effect of Fire exposure Time on the Flexural Capacity (Saafi (2002))

19. Analytical Work Abbasi and Hogg (2005) • Proposed a model to predict the time to failure of GFRP beams in a fire • Based on ACI design codes where time and temperature dependent values of rebar and concrete strength and modulus replaces the static design values. • The base equations are modified to remove safety factors • The equations are as follows When rebar failure occurs When concrete failure occurs

20. Analytical Work Abbasi and Hogg (2005) Rebar stress when concrete fails Concrete stress when concrete fails • When flexural moment exceeds the flexural capacity of the beam failure • occur • Performance of the model was in very good agreement with experimental • results

21. Analytical Work Abbasi and Hogg (2005) Figure : Flexural Capacity and Failure Time for a Beam Reinforced with Steel and Its Comparison with FRP Reinforcement (Abbasi and Hogg (2005))

22. Conclusions • The amount of research conducted to evaluate the performance of • FRP reinforce bema under elevated temperature is limited • Adequate fire endurance of reinforced concrete is usually provided • by the minimum cross sectional dimensions and concrete cover • Critical temperature for steel is commonly established at 593 ˚C • Critical temperature for FRP is not yet established • The most critical issue for FRP reinforced concrete at elevated • temperature is the bond between concrete and FRP

23. Thank You