Performance and Parametric Analysis of Flexural Strengthening for RC Beams with NSM-CFRP Bars
Publication: Journal of Composites for Construction
Volume 18, Issue 4
Abstract
The flexural strengthening of concrete structures by the near-surface-mounted (NSM) method has proven to be a reliable alternative to the existing externally bonded (EB) method using carbon fiber–reinforced polymer (CFRP) composites. However, the NSM method has not been used as widely as the EB method, and many factors influencing the effectiveness of NSM-CFRP bars still need to be investigated and clarified. Therefore, a total of eight concrete beams were constructed and tested. The effects of different parameters, including the number of NSM-CFRP bars, prestressing in NSM-CFRP, and the type of end treatment—for reduced/delayed end bond failure—on the performance of the strengthened beams were investigated. The test results demonstrated that the use of NSM-CFRP bars is effective in increasing the flexural capacity of concrete beams. However, when the number of CFRP bars was increased from one to two, only the postyielding cross-section stiffness of the beam displayed a better performance. The prestressed beams exhibited a higher cracking load and a higher yield load compared with the nonprestressed beams. The prestressing considered in this regard was 40% of the ultimate capacity. Three end treatments were considered: -shaped steel-plate hoops, expanded groove at the ends of the bar, and reduced resin modulus at the bar ends when prestress is released. Of these, the end treatment using a -shaped steel-plate hoop developed in this article was simple and effective and was capable of increasing the ductility of both prestressed and nonprestressed beams. By addressing the effects of the aforementioned factors on the NSM strengthened beams, this paper offers valuable information for the increased implementation of this technique.
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Acknowledgments
The authors would like to acknowledge financial support from the National Program on Key Basic Research Project (No. 2012CB026200), the National “Twelfth Five-Year” Plan for Science and Technology (No. 2011BAB03B09), the Natural Science Foundation of Jiangsu Province, China (No. BK2010015), and the National High Technology Research and Development Program of China (No. 2012AA03A204).
References
American Concrete Institute (ACI). (2008). “Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures.”, Farmington Hills, MI.
Asplund, S. O. (1949). “Strengthening bridge slabs with grouted reinforcement.” ACI Struct. J., 20(6), 397–406.
Badawi, M. (2007). “Monotonic and fatigue flexural behavior of RC beams strengthened with prestressed NSM CFRP rods.” Ph.D. thesis, Dept. of Civil and Environmental Engineering, Univ. of Waterloo, Waterloo, ON, Canada.
Badawi, M., and Soudki, K. (2009). “Flexural strengthening of RC beams with prestressed NSM CFRP rods–experimental and analytical investigation.” Constr. Build. Mater., 23(10), 3292–3300.
Badawi, M., Wahab, N., and Soudki, K. (2011). “Evaluation of the transfer length of prestressed near surface mounted CFRP rods in concrete.” J. Constr. Build. Mater., 25(3), 1474–1479.
Barros, J., and Dias, S. (2006). “Near surface mounted CFRP laminates for shear strengthening of concrete beams.” Cem. Concr. Compos., 28(3), 276–292.
Bianco, V., Barros, J., and Monti, G. (2010). “New approach for modeling the contribution of NSM FRP strips for shear strengthening of RC beams.” J. Compos. Constr., 36–48.
Blaschko, M., and Zilch, K. (2003). “Bond behavior of CFRP strips glued into slits.” Proc., 6th Int. Symp. on Fiber Reinforced Polymers for Reinforced Concrete Structures (FRPRCS-6), American Concrete Institute, Farmington Hills, MI.
Casadei, P., Nanni, A., Alkhrdaji, T., and Thomas, J. (2005). “Performance of double-T prestressed concrete beams strengthened with steel reinforcement polymer.” Adv. Struct. Eng., 8(4), 427–442.
Choi, H., West, J., and Soudki, K. (2011). “Effect of partial unbonding on prestressed near-surface-mounted CFRP-strengthened concrete T-Beams.” J. Compos. Constr., 93–102.
De Lorenzis, L., Lundgren, K., and Rizzo, A. (2004). “Anchorage length of near-surface mounted fiber-reinforced polymer bars for concrete strengthening—Experimental investigation and numerical modeling.” ACI Struct. J., 101(2), 269–278.
De Lorenzis, L., and Nanni, A. (2001a). “Characterization of FRP rods as near surface mounted reinforcement.” J. Compos. Constr., 114–121.
De Lorenzis, L., and Nanni, A. (2001b). “Shear strengthening of reinforced concrete beams with NSM fiber-reinforced polymer rods.” ACI Struct. J., 98(1), 60–68.
De Lorenzis, L., and Nanni, A. (2002). “Bond between near-surface mounted FRP rods and concrete in structural strengthening.” ACI Struct. J., 99(2), 123–133.
De Lorenzis, L., Rizzo, A., and La Tegola, A. (2002). “A modified pull-out test for bond of near-surface mounted FRP rods in concrete.” Compos. B: Eng., 33(8), 589–603.
De Lorenzis, L., and Teng, J. G. (2007). “Near-surface mounted FRP reinforcement: An emerging technique for strengthening structures.” Compos. B: Eng., 38(2), 119–143.
El-Hacha, R., and Gaafar, M. (2011). “Flexural strengthening of reinforced concrete beams using prestressed, near-surface-mounted CFRP bars.” PCI J., 56(4), 134–151.
El-Hacha, R., and Rizkalla, S. H. (2004). “Near-surface-mounted fiber-reinforced polymer reinforcements for flexural strengthening of concrete structures.” ACI Struct. J., 101(5), 717–726.
Hajihashemi, A., Mostofinejad, D., and Azhari, M. (2011). “Investigation of RC beams strengthened with prestressed NSM CFRP laminates.” J. Compos. Constr., 887–895.
Hassan, T., and Rizkalla, S. (2003). “Investigation of bond in concrete structures strengthened with near surface mounted carbon fiber reinforced polymer strips.” J. Compos. Constr., 248–257.
Hassan, T., and Rizkalla, S. (2004). “Bond mechanism of near-surface-mounted fiber-reinforced polymer bars for flexural strengthening of concrete structures.” ACI Struct. J., 101(6), 830–839.
Hawileh, R. A. (2012). “Nonlinear finite element modeling of RC beams strengthened with NSM FRP rods.” Constr. Build. Mater., 27(1), 461–471.
Jung, W. T., Park, Y. H., Park, J. S., Kang, J. Y., and You, Y. J. (2005). “Experimental investigation on flexural behavior of RC beams strengthened by NSM CFRP reinforcements.” Proc., 7th Int. Symp. on Fiber Reinforced Polymers for Reinforced Concrete Structures, American Concrete Institute, Farmington Hills, MI, 795–805.
Kotynia, R. (2007). “Analysis of the flexural response of NSM FRP-strengthened concrete beams.” Proc., 8th Int. Symp. on Fiber Reinforced Polymers for Reinforced Concrete Structures (FRPRCS-8), American Concrete Institute, Farmington Hills, MI, 16–18.
Lee, D., and Cheng, L. J. (2011). “Assessing the strengthening effect of various near-surface-mounted FRP reinforcements on concrete bridge slab overhangs.” J. Compos. Constr., 615–624.
Nordin, H., and Täljsten, B. (2006). “Concrete beams strengthened with prestressed near surface mounted CFRP.” J. Compos. Constr., 60–68.
Oehlers, D. J., Rashid, R., and Seracino, R. (2008). “IC debonding resistance of groups of FRP NSM strips in reinforced concrete beams.” Constr. Build. Mater., 22(7), 1574–1582.
Quattlebaum, J. B., Harries, K. A., and Petrou, M. F. (2005). “Comparison of three flexural retrofit systems under monotonic and fatigue loads.” J. Bridge Eng., 731–740.
Razaqpur, A. G., Shedid, M., and Petrina, D. (2011). “Behavior of beams strengthened with novel self-anchored near-surface-mounted CFRP bars.” J. Compos. Constr., 625–634.
Soliman, S. M., El-Salakawy, E., and Benmokrane, B. (2008). “Flexural behaviour of concrete beams strengthened with near surface mounted FRP bars.” Proc., 4th Int. Conf. on Fiber Reinforced Polymer Composites in Civil Engineering (CICE2008), International Institute for FRP in Construction (IIFC), Kingston, ON, Canada, 22–24.
Sun, Z. Y., Wu, G., Wu, Z. S., and Luo, Y. B. (2011). “Flexural strengthening of concrete beams with near-surface mounted steel-fiber-reinforced polymer composite bars.” J. Reinf. Plast. Compos., 30(18), 1529–1537.
Teng, J. G., De Lorenzis, L., Wang, B., Li, R., Wong, T. N., and Lam, L. (2006). “Debonding failures of RC beams strengthened with near surface mounted CFRP strips.” J. Compos. Constr., 92–105.
Wahab, N., Soudki, K., and Topper, T. (2012). “Experimental investigation of bond fatigue behavior of concrete beams strengthened with NSM prestressed CFRP rods.” J. Compos. Constr., 684–692.
Wahab, N., Soudki, K. A., and Topper, T. (2011). “Mechanism of bond behavior of concrete beams strengthened with near-surface-mounted CFRP rods.” J. Compos. Constr., 85–92.
Wu, G., Zeng, Y. H., Wu, Z. S., and Feng, W. Q. (2013). “Experimental study on the flexural behavior of RC beams strengthened with steel-wire continuous basalt fiber composite plates.” J. Compos. Constr., 208–216.
Wu, Z., Iwashita, K., and Sun, X. (2007). Structural performance of RC beams strengthened with prestressed near-surface-mounted CFRP tendons, ACI Special Publication SP-245-10, American Concrete Institute, Farmington Hills, MI, 165–178.
Wu, Z. S., Iwashita, K., Hayashi, K., Higuchi, T., Murakami, S., and Koseki, Y. (2003). “Strengthening prestressed-concrete girders with externally prestressed PBO fiber reinforced polymer sheets.” J. Reinf. Plast. Compos., 22(14), 1269–1286.
Yost, J. R., Gross, S. P., Dinehart, D. W., and Mildenberg, J. J. (2007). “Flexural behavior of concrete beams strengthened with near-surface-mounted CFRP strips.” ACI Struct. J., 104(4), 430–437.
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Published In
Journal of Composites for Construction
Volume 18 • Issue 4 • August 2014
Copyright
© 2013 American Society of Civil Engineers.
History
Received: Jun 6, 2013
Accepted: Oct 26, 2013
Published online: Nov 28, 2013
Discussion open until: Apr 28, 2014
Published in print: Aug 1, 2014
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