Concrete Today May 2010 - the Irish Concrete Federation

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concrete today - fibre reinforced polymer Figure 3 – Test rig and test arrangement Test Test slabs Concrete Strength (N/mm2) S1 S2 S3 S4 LRS-0.6%- 12mm-125 C LRS-0.6%- 12mm-125 T&B LRS-0.15%- 8mm-300 C LRS-0.15%- 8mm-300 T&B Failure load (kN) Deflection at failure (mm) Maximum strain on bar at failure(µE) Failure mode 64.7 235 16 10534 Concrete crushing 68.1 344 20 4096 Concrete crushing 69.5 255 19 18653 Concrete crushing/ FRP rupture 66.7 269 13 10475 Concrete crushing/ FRP rupture It was found that the slabs reinforced with two reinforcement layers were stiffer than the slabs reinforced with single mid-depth reinforcement. However the significant effect of CMA can be seen through comparing S2 with S4. Slab S2 (0.60% GFRP) was reinforced with 4 times as much reinforcement as S4 (0.15% GFRP), but the maximum load capacity difference between those two slabs was only 17% of slab S4. Even more striking is the fact that S1 (0.60%) failed at 90% of the failure load of S3 (0.15%); both with middepth reinforcement. A comparison of two slabs, one with steel reinforcement and the other with GFRP, is presented in Table 2. This shows that Table 1: Test results Test Results and Discussion The four slabs were used to analyse the influence of reinforcement percentage and position on the performance of the laterally restrained slabs. The first two slabs were reinforced with 0.6% GFRP reinforcement and the other two with 0.15%. Among those two, one was reinforced with single mid-depth reinforcement and the other was reinforced with two layer conventional reinforcing method. The test results are provided in Table 1. Load versus deflection behaviour of the four slabs is shown in Figure 4. Figure 4 – Load Vs Deflection of slabs concrete today 22
concrete today - fibre reinforced polymer Figure 5: Condition of GFRP inside a tested slab (No indication of rupture on bars) Figure 6: Ruptured GFRP during material test the failure load is very similar for both slabs. This shows that CMA is the main contributor to the ultimate capacity of the slabs and since the capacity is far in excess of the design load the lack of ductility is not a significant issue. Serviceability on the other hand, is ensured by the GFRP; in the case of crack width when placed near the surface only. Also there was no evidence of complete GFRP rupture when the embedded bars were examined after tests (Figure 5 and Figure 6). III. Compared with laterally restrained slabs reinforced with an equivalent amount of steel reinforcement those reinforced with GFRP showed excellent performance at ultimate load. Therefore GFRP reinforcement can be a substitute for steel in restrained slabs such as bridge deck slabs. Acknowledgement • Irish Concrete Society for awarding a Travel Bursary to attend the Fibre Reinforced Polymer Reinforcement for Concrete Structures 2009 Conference. • Schock Bauteile GmbH, Germany for generously providing GFRP (ComBAR) material for the research and staff at QUB for their supports with experiments. • Sengenia (http://www.sengenia.com/) for providing Fibre Optic Sensors for the research. Reference 1. Read, J.A, ‘FBECR, The need for correct specification and quality control’, Concrete, Vol.23, 8, 23-27, 1989. 2. Clarke, J.L., The need for durable reinforcement, Alternative Materials for Reinforcement and Prestressing of Concrete, Chapman & Hall, (1993). 3. Taylor, S.E. and Barry Mullin, ‘Arching action in FRP reinforced concrete slabs’, Construction and Building Materials, 20, 71-80, (2006). 4. Tharmarajah, G., Robinson, D.J, Taylor, S.E & Cleland, D.J, FRP reinforcement for laterally restrained slabs, Proceedings of Bridge and Infrastructure Research in Ireland 2008, December 2008. 5. Tharmarajah, G., Cleland, D.J., Taylor, S.E & Des Robinson, Compressive Membrane Action in FRP reinforced slabs, Proceedings of Fibre Reinforced Polymer Reinforcement for Concrete Structures 2009, July 2009. 6. Taylor, S.E., Rankin, G.I.B., Cleland, D.J, ‘Arching action in highstrength concrete slabs’, Proceedings of the Institution of Civil Engineers Structures and Buildings, Institution of Civil Engineers,Vol.146,4, 353-362, 2001. Table 2: Comparison of test results with some previous research results Conclusion The following conclusions were drawn from this experimental study. I. Restrained slabs can have substantial ultimate capacity even with minimum amounts of reinforcement. II. GFRP reinforcement in laterally restrained slabs showed excellent service behaviour in terms of deflections and in terms of crack widths. Slab Reinforcement Reinforcement yield stress (N/ mm 2 ) S5 (Taylor et al., 2006) S6 (Taylor et al., 2006) GFRP 0.5% at Mid depth Steel 0.5% at Mid depth fcu (N/ mm 2 ) Failure load kN 504 67.9 200 12.0 530 85.0 210 15.0 Deflection at 115 kN load (mm) concrete today 23
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