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Fire behaviour of FRP wrapped square reinforced concrete columns
Chowdhury, E. U.; Bisby, L. A.; Green, M. F.; Bénichou, N.; Kodur, V. K. R.
http://irc.nrc-cnrc.gc.ca
F i r e b e h a v i o u r o f F R P w r a p p e d s q u a r e r e i n f o r c e d
c o n c r e t e c o l u m n s
N R C C - 5 0 2 5 1
C h o w d h u r y , E . U . ; B i s b y , L . A . ; G r e e n , M . F . ;
B é n i c h o u , N . ; K o d u r , V . R .
2 0 0 8 - 0 9 - 2 1
A version of this document is published in / Une version de ce document se trouve dans:
9th IAFSS, Karlsruhe, Germany, Sept. 2008, .pp 1-8
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E.U. Chowdhury
1, L.A. Bisby
2, M.F. Green
1, N. Benichou
3and V.K.R. Kodur
4 1 Department of Civil Engineering, Queen’s University, Kingston, Canada 2 BRE Centre for Fire Safety Engineering, University of Edinburgh, Scotland, UK 3 National Research Council of Canada, Ottawa, Canada 4 Department of Civil and Environmental Engineering, Michigan State University, Michigan, USAAbstract
Numerous applications of fibre reinforced polymers (FRPs) have demonstrated good performance in retrofitting and repairing deteriorated reinforced concrete structures, both through research studies and through practical field applications. However, a there is a paucity of information on FRP strengthening systems at elevated temperatures, and the perceived susceptibility of these systems in fire, still discourages their use in many applications. As part of a larger ongoing research program, an experimental and analytical study is underway focusing on the fire behaviour of FRP strengthened square reinforced concrete (RC) columns.
Experimental Program
The experimental program consists of full‐scale fire tests on three FRP strengthened RC square columns (one of which has been tested to date). The tested column was strengthened with glass FRP (GFRP) hoop wraps and protected with an insulation system consisting of a spray‐applied cementitious mortar and epoxy coating. The tied reinforced column was 3810 mm long and cast from carbonate aggregate concrete. The percentage of longitudinal steel in the column was 1.21% with a concrete cover of 50 mm. During the fire test, the column was under a sustained concentric load of 3093 kN, which was 69% of the predicted room temperature ultimate strength, and was exposed to ASTM E‐119 fire. The column was considered to have failed when the hydraulic jack could no longer maintain the load.
The FRP strengthened square RC column protected with the fire protection system was capable of achieving a fire endurance rating of more than 4 hours. Figure 1 shows the FRP strengthened col‐
fire endurance of the member under applicable loads must be considered, rather than only the specific performance of the FRP material. Visual observations made during the fire tests indicated that the insulation remained intact for more than 4 hours of exposure to the standard fire with only minimal cracking.
Analytical Modelling
A numerical model is being developed to predict both the heat transfer and structural response of FRP strengthened square reinforced concrete columns in fire. An explicit finite difference method is used to predict the temperatures within the column and the Column Deflection Curve method presented in Chen and Atsuta [1] is used to determine its structural behaviour. The structural model accounts for the non‐linear mechanical response of all constituents, the confining effect of the FRP wraps, and the second‐order moments in the columns.
Preliminary results from the heat transfer model on a plain 305 mm square reinforced concrete column are presented in Figure 3 where they are validated against experimental results from tests by Lie and Woollerton [2]. It was found that the predictions from the current heat transfer model agree well with the experimental results.
The structural analysis model has been validated for the room temperature case against experimental results presented in Fitzwilliam [3] on 152 mm diameter circ‐
(a) (b) Figure 1 – FRP strengthened square RC column (a) before and (b) after fire test (a) (b) Figure 3 – Variation in temperature within RC column (a) along the line AB and (b) AC Figure 4 – Predicted and observed [3] axial load‐lateral deflection behaviour of RC circular columns of various lengths with increasing applied load
References
[1] Chen, W.F., Atsuta, T., Theory of Beam‐Columns: V. 1’, McGraw Hill, 1976, 513 pp. [2] Lie, T.T., Woollerton, J.L., Fire resistance of reinforced concrete columns, Internal Report No. 569, Institute for Research in Construction, National Research Council of Canada, 1988, 302 pp. [3] Fitzwilliam, J. M. Fibre‐reinforced polymer wraps for slender eccentrically‐loaded reinforced concrete columns, M.Sc. Thesis, Queen’s University, Kingston, Canada, 2002.Further Work
Additional full‐scale fire tests are planned for 2008‐2009 to validate the heat transfer analysis for FRP wrapped and insulated square RC columns. Small‐scale materials tests are also in progress on various externally‐bonded FRP strengthening systems to investigate the mechanical and bond properties and FRP confinement effectiveness at elevated temperatures.
406 mm 3 layers of GFRP wrap 38 mm insulation system Intumescent paint 2 6 8 4 1 16 7 3 Thermocouples Figure 2 – Temperatures recorded at various locations in the FRP strengthened RC column during fire test
umn square RC column before and immediately after failure. Figure 2 shows that the temperature of the FRP wrap rem‐ ained below 100 C for about only 30 min minutes, although the column continued to carry its service load. This shows that the fire endurance of FRP strengthened members need to be considered in holistic way, in that the
ular columns. The comparison in Fig‐ ure 4 shows that the model can predict the maximum axial load carrying cap‐ acity and can also capture the struct ural behaviour of circular concrete col‐ umns satisfactorily at room tempera‐ ture. Extension of the model to account for the effects of elevated temperature is currently underway.
