Structural Behavior of SFRC Beams strengthened with GFRP Laminates: An Experimental and Analytical Investigation

1 Biological and Applied Sciences Vol.59: e16161071, January-December 2016 http://dx.doi.org/10.1590/1678-4324-2016161071 ISSN 1678-4324 Online Edition BRAZILIAN ARCHIVES OF BIOLOGY AND TECHNOLOGY A N I N T E R N A T I O N A L J O U R N A L Structural Behavior of SFRC Beams strengthened with GFRP Laminates: An Experimental and Analytical Investigation M.Mariappan 1*, P.N.Raghunath 2, M.Sivaraja3. 1 Department of Civil Engineering, Adhiparasakthi Engineering College; 2Annamalai University, Chidambaram, India; 3Department of Civil Engineering, N.S.N. College of Engg. & Tech., Karur, India. ABSTRACT This paper presents the experimental results of a reinforced concrete beams (RC) strengthened with internal steel fibers (SF) and external glass fiber reinforced polymer laminates (GFRP). The research work studied the load carrying capacity, deformation, crack width and ductility of the reinforced concrete beams strengthened with different steel fiber ratios and steel fiber reinforced concrete beams strengthened with three different glass fiber reinforced polymer laminates of two different thickness. The experimental results clearly shows that incorporating steel fibers in to the reinforced concrete beams reduced the crack width and distribute the crack evenly and also increases the bonding between tension face of the beam with glass fiber reinforced polymer laminates. The results also shows that glass fiber reinforced polymer laminates strengthened steel fiber reinforced concrete beams increases the flexural strength and ductility as compared with unstrengthened counterpart. In addition to this experimental work, theoretical calculations were done to find the ultimate load carrying capacity of the beam tested, and also compared with the experimental results. Key words: RC, FRC, GFRP, SFRC, Ductility * Author for correspondence: Braz. Arch. Biol. Technol. v.59: e161071 Jan/Dec 2016 Spec Iss 2 2 Mariappan M et al. INTRODUCTION Many research and development in the reinforced concrete structural elements using high performance materials has progressed significantly in recent years. Previous researchers conducted experimental and analytical investigations on debonding of hybrid FRPs for flexural strengthening of RC beams[1]. One or two layers of CFRP or GFRP sheets were used for strengthening purpose [13,14]. The test results shows that adding the existing three-point bending test method for a small RC beam, debonding failure can be induced in the RC beams strengthened with FRPs[15,19]. The modifications are performed by including a saw-cut in the middle of the beam span and adding a reinforcing bar to prevent shear failure [8,9]. The experimental results show that the beam strengthened with stiffer and thinner layers of FRPs have higher debonding strengths than the beams strengthened with less stiff and the thicker layers of FRPs[13,20]. Therefore, the debonding level of the hybrid FRP plates is more influenced by the thickness of the strengthening materials than by its stiffness[4,5]. The debonding strength is also influenced by the arrangement of layers and the higher debonding strengths were achieved when a layer of CFRP is attached to the concrete prior to a GFRP layer [6,7]. Previous researcher[2] conducted experimental research on the fatigue and post-fatigue static behaviour of reinforced concrete beams strengthened with glass or carbon fiber reinforced polymer sheets placed either vertically or obliquely. The test results have shown that externally bonded CFRP or GFRP to the lateral and bottom faces of a beam can increase the first crack load and ultimate strength greatly, arrest concrete crack extension and enhance the rigidity of strengthened beams [10,11]. The CFRP strengthened beam has the highest ultimate strength but the lowest deflection and the diagonal GFRP reinforcing arrangement is more effect than the vertical arrangement in enhancing the shear strength and stiffness[12]. From experimentally investigated the performance of RC beam strengthened with externally bonded FRP composites[3], the response of control and strengthened beams were compared and efficiency and effectiveness of different schemes were evaluated. It was observed that tension side bonding of CFRP sheets with U-shaped end anchorages is very efficient in flexural strengthening, whereas bonding the inclined CFRP strips to the side of RC beams are very effective in improving the shear capacity of beams[16]. This paper focuses on the study on structural performance of reinforced concrete beams with steel fibers of different ratios and steel fiber reinforced concrete beams with GFRP laminates of different types and different thickness. An analytical study is also involved to validate the experimental results using ACI 440-2R equation [17,18] . EXPERIMENTAL STUDY MATERIALS The concrete used for all beam specimens had a compressive strength of 24MPa. The concrete consisted of 370 kg/m3 of ordinary Portland cement, 584.6 kg/m3 of fine aggregate, 701.5 kg/m3 of coarse aggregate, 467.68 kg/m3 of medium aggregate, 0.36 water/cement ratio and 0.8% of hyper plasticizer. The reinforcement of high yield strength deformed bars of characteristic strength 456MPa were used for the longitudinal reinforcement. The lateral ties consisted of mild steel bars of yield strength 300MPa. The specimens were provided with 8mm diameter stirrups at 150 mm spacing. Braz. Arch. Biol. Technol. v.59: e161071 Jan/Dec 2016 Spec Iss 2 3 SFRC Beams strengthened with GFRP Laminates Steel Fibres The steel fibres used were Dramix steel fibres. The physical and mechanical properties of steel fibres are presented in Table 2. Glass Fibre Reinforced Polymer Glass fibres reinforced polymer having the following configurations were used for the investigation. i. Chopped Strand Mat (CSM) ii. Uni-Directional Cloth (UDC) iii.Woven Roving (WR) The glass fibre reinforced polymer fabrics were applied on the soffit of the beam specimens using epoxy adhesive. The physical and mechanical properties of GFRP laminates are presented in Table 1. BEAM DETAILS Twenty two RC rectangular beam specimens having 150mm x 250mm crosssection and 3000 mm length were cast for the present research work. Longitudinal steel ratio adopted for the beam specimen was 0.603% (2 bars, 12 mm diameter). 2-legged 8 mm diameter shear stirrups were provided at 125 mm c/c, in order to avoid any shear failure and ensure flexural action of beams up to failure. The detailing of internal reinforcement is shown through Fig.1. Details of the twenty two specimens prepared for experimental work are presented in Table 3. The beams had three different fibre volume fractions and were laminated with GFRP plates of 3 mm and 5 mm thickness. The fibres in GFRP also varied in their configuration, viz., Woven roving (WR), Chopped Strand Mat (CSM) and UniDirectional Cloth (UDC). Fig.1 Reinforcement Details of Beam Specimen Sl. No. Type of Fibre in GFRP Thickness (mm) Tensile S (...truncated)