Strengthening of Existing RC Two-Way Slabs using New Combined FRP fabric/rod Technique

Document Type: Regular Paper

Authors

1 Ph.D. In Structural Engineering, Faculty of Civil Engineering, Semnan University, Semnan, Iran

2 Associate Professor, Faculty of Civil Engineering, Semnan University, Semnan, Iran

3 Professor, Faculty of Civil Engineering, Semnan University, Semnan, Iran

Abstract

This study presents the results of an experimental program to investigate the effectiveness of an innovative combined FRP technique using combination of externally bonded (EB) FRP fabrics and near surface mounted (NSM) FRP rods for flexural strengthening of existing reinforced concrete (RC) two-wayslabs with low clear cover thickness. Three full-scale RC slabs (1500×1500×120 mm) were tested under monotonic four-point bending. One slab was kept un-strengthened as the control specimen, one slab was strengthened using NSM GFRP rods, and the other one slab was strengthened using combination of EB CFRP fabrics and NSM GFRP rods. The load-deflection responses, strain measurements, and failure modes of the tested slabs were studied and discussed. The behavior of the slab strengthened with this technique was compared to the behavior of the slab strengthened with GFRP rods. The test results confirmed the feasibility and efficacy of this technique in improving the flexural behavior of RC two-way slabs. Strengthened slabs showed an increase in flexural capacity between 250 and 394% over the control specimen. The slab strengthened using this technique showed higher ductility compared to the slab strengthened using GFRP rods. A 3D nonlinear numerical model was also developed using the finite element (FE) method to predict the flexural behavior of the tested slabs. A good agreement between experimental and numerical results was observed.

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[1] ACI (American Concrete Institute). (2008). ACI 440.2R-08: "Guide for the design and construction of externally bonded FRP system for strengthening concrete structures". American Concrete Institute, Farmington Hills, MI, USA.

[2] Badawi, M., Soudki, K. (2009). "Flexural strengthening of RC beams with prestressed NSM CFRP rods–experimental and analytical investigation". Constr Build Mater, 23(10), pp.3292-3300.

[3] Anwarul Islam, AKM. (2009). "Effective methods of using CFRP bars in shear strengthening of concrete girders". Eng Struct J, 31, pp.709–714.

[4] De Lorenzis, L., Teng, JG. (2007). "Near-surface mounted FRP reinforcement: An emerging technique for strengthening structure". J Compos Part B Eng, 38(2), pp.119–143.

[5] El-Hacha, R., Riskalla, SH. (2004). "Near-surface-mounted fiber-reinforced polymer reinforcements for flexural strengthening of concrete structures". ACI Struct J, 101(5), pp.717–726.

[6] Barros, JAO., Dias, SJE., Lima, JLT. (2007). "Efficacy of CFRP-based techniques for the flexural and shear strengthening of concrete beams". J Cem Concr Compos, 29(3), pp.203–217.

[7] Ceroni, F. (2010). "Experimental performances of RC beams strengthened with FRP materials". Constr Build Mater, 24(9) , pp.1547-1559.

[8] Jalali, M., Sharbatdar, MK., Chen, JF., Jandaghi Alaee, F. (2012). "Shear strengthening of RC beams using innovative manually made NSM FRP bars". Constr Build Mater, 36, pp.990–1000.

[9] Barros, JAO., Baghi, H., Dias, SJE., Gouveia, AV. (2013). "A FEM-based model to predict the behaviour of RC beams shear strengthened according to the NSM technique". Eng Struct J, 56, pp.1192–1206.

[10] Sharaky, IA., Torres, L., Comas, J., Barris, C. (2014). "Flexural response of reinforced concrete (RC) beams strengthened with near surface mounted (NSM) fibre reinforced polymer (FRP) bars". Compos Struct J, 109, pp.8–22.

[11] Bonaldo, E., Barros, JAO., Lourenco, PB. (2008). "Efficient strengthening technique to increase the flexural resistance of existing RC slabs". J Compos Constr, 12(2), pp.149–159.

[12] Elgabbas, F., El-Ghandour, AA., Abdelrahman, AA., El-Dieb, AS. (2010). "Different CFRP strengthening techniques for prestressed hollow core concrete slabs: Experimental study and analytical investigation". Compos Struct J, 92, pp.401–411.

[13] Dalfré, GM., Barros, JAO. (2013). "NSM technique to increase the load carrying capacity of continuous RC slabs". Eng Struct J, 56, pp.137–153.

[14] Mostakhdemin Hosseini, MR., Dias, SJE., Barros, JAO. (2014). "Effectiveness of prestressed NSM CFRP laminates for the flexural strengthening of RC slabs". Compos Struct J, 111, pp.249–258.

[15] Breveglieri, M., Barros, JAO., Dalfré, GM., Aprile, A. (2012). "A parametric study on the effectiveness of the NSM technique for the flexural strengthening of continuous RC slabs". Compos Part B Eng, 43(4), pp.1970–1987.

[16] Foret, G., Limam, O. (2008). "Experimental and numerical analysis of RC two-way slabs strengthened with NSM CFRP rods". Constr Build Mater, 22(10), pp.2025–2030.

[17] ANSYS – release version 11. (2007). "A finite element computer software theory and user manual for nonlinear structural analysis". ANSYS 2007, Inc. Canonsburg, PA.

[18] ACI (American Concrete Institute). (1999). ACI 318-99: "Building code requirements for structural concrete, American Concrete Institute". Farmington Hills, MI, USA.

[19] William, KJ., Warnke, EP. (1975). "Constitutive model for the triaxial behavior of concrete". IABSE Proc., Int. association for bridge and structural engineering, Zürich, 19, pp.174.