In the last two decades, the use of fibre-reinforced polymer (FRP) reinforcement for retrofitting RC structures has become a field of much research interest. FRPs have several advantages over classic strengthening techniques, such as design flexibility, ease of use, and corrosion resistance. Methods for shearstrengthening of RC beams using FRP composites include externally bonded (EB) sheets (Dirar et al., 2012) or plates (Mofidi et al., 2014), near-surface mounted (NSM) bars (Rahal and Rumaih., 2011), prestressed carbon fibre reinforced polymer (CFRP) straps (Dirar et al., 2013) and embedded CFRP rods (Valerio et al., 2009; Mofidi et al., 2012a). Compared with the EB and NSM shearstrengthening methods, the deep embedment (DE) technique, also known as the embedded through section (ETS) technique (Valerio and Ibell., 2003; Valerio et al., 2009; Mofidi et al., 2012a), offers better bond performance between the concrete and the FRP reinforcement (Chaallal et al., 2011).
used to strengthen an existing structure. Twelve T-beams, two of which were maintained as a control, were tested. The beams had the following dimensions: 152 mm × 381 mm × 2743 mm. They were retrofitted with U-wrapped continuous FRP fabric in one or two layers with and without anchorage. Of the ten strengthened beams, eight were retrofitted with CFRP and the remainder with aramid composite. For the anchorage, the authors used the technique described by Khalifa et al. (2000). In addition, the small longitudinal steel reinforcement ratio led the authors to strengthen the beams in flexure in order to inhibit any premature failure in flexure. The flexural strengthening was applied to both critical positive and critical negative moment regions. The beams were tested under three-point loads with the load applied at distance 2.4 m from the support. In the beams with no anchorage, failure occurred by premature debonding of the FRP, accompanied by severe delamination. The gain in shear resistance was 11% to 16%, depending on the number of FRP layers. The beams with anchored FRP achieved higher gains, ranging from 35% to 27%, depending on the number of FRP layers. Failure in this case was caused by loss of anchorage. The addition of a second CFRP layer to the specimens with anchorage did not result in a capacity increase. The authors noted that the gains achieved are small compared to those predicted by theory. This behaviour was attributed to deep beam action by the authors, who strongly recommended further investigation into this phenomenon. It must be said that an a/d ratio of 2.4 is at the upper limit of what can be considered as a deep beam. It must also be noted that the resistance of concrete in compression was around 20 MPa. The quality of the concrete substrate could also explain the results obtained. In this context, it would have been interesting to know more details on the state of the concrete substrate and on the surface preparation prior to application of FRP.
R. Balamuralikrishnan and C. Antony Jeyaseha (2009) this paper explores the flexural behaviour of carbon fibre reinforced polymer (CFRP) strengthened reinforcedconcrete (RC) beams. For flexural strengthening of RC beams, total ten beams were cast and tested over an effective span of 3000 mm up to failure under monotonic and cyclic loads. The beams were designed as under-reinforcedconcretebeams. Eight beams were strengthened with bonded CFRP fabric in single layer and two layers which are parallel to beam axis at the bottom under virgin condition and tested until failure; the remaining two beams were used as control specimens. Static and cyclic responses of all the beams were evaluated in terms of strength, stiffness, ductility ratio, energy absorption capacity factor, compositeness between CFRP fabric and concrete, and the associated failure modes. The theoretical moment-curvature relationship and the load-displacement response of the strengthened beams and control beams were predicted by using FEA software ANSYS. Comparison has been made between the numerical (ANSYS) and the experimental results. The results show that the strengthened beams exhibit increased flexural strength, enhanced flexural stiffness, and composite action until failure.
Concrete structures deteriorate over time, and therefore imple- menting a design approach aimed at rehabilitating critical struc- tural members such as beams, columns and bridge girders is necessary. One of the problems encountered in these critical mem- bers is their deficiency in sustaining the applied shear load over time. Fiber-Reinforced Polymers (FRP) are composite systems of fibers embedded in a polymeric matrix. 3 Rehabilitation of Rein- forced Concrete (RC) members using FRP was introduced more than two decades ago. 4 Multiple studies, such as the ones con- ducted by Khalifa and Nanni, 3 Bimal and Hiroshi, 5 and Pellegrino and Modena, 6,7 have shown that applying FRP to RC beams increases the overall shear capacity of a structural member. Due to the complex nature of shear design even in simple reinforced con- crete beams, determining the exact contribution of the Fiber Rein- forced Polymers in shear is still under investigation and the results thus far are not really converging toward a generalized prediction model. In order to better understand the behavior of FRP applied externally to an RC or prestressed concrete member, a literature review was conducted to assess the current state of the art for shear-strengthening of members using fiber-reinforced polymers (FRP), particularly carbon fiber-reinforced polymers (CFRP) which is the most common material used for shear-strengthening.
Kaushal Parikh (2012) et al. carried out an experimental and analytical investigation on preloaded retrofitted beam for enhancement in flexural strength. They investigated total seventeen beams out of which two were control beam and fifteen were preloaded at 0%, 40% and 90% strength of control beam. They applied two types of arrangements on beam consisting of Traditional (T) arrangement & New effective (N) arrangement. They also carried out analytical investigation by using finite element modelling. Finally authors arrived on conclusion that beams with New effective arrangement shifts the flexural crack away from flexural region and hence by delaying the debonding, proved a good solution for retrofitting technique. They also found that load vs. deflection between predicted analytically and experimentally values are not varied more than 5% and failure mode was remarkable compared.
Three series of simply supported hybrid-fibre-reinforced self-compacting concreteT-beams subjected to four-point symmetrically placed vertical load were experimentally investigated. The influence of the following variables was studied: the fibre type, the fibre content, the stirrup ratio and the flange size. Failures were consistently shear or shear – flexure failures, except in five T-beam specimens where the failure was dominated by flexural cracks. The results showed that hybrid fibres can evidently enhance the ultimate shear load. The addition of hybrid fibres in adequate amounts can change the failure mode. The influence of different flange size on the ultimate shear load of the T-beams should be considered. Three methods were proposed – the ‘ effective width ’ , ‘ form factor ’ and ‘ shear funnel ’ – for predicting the ultimate shear load of steel-fibre-reinforced self-compacting concreteT-beams, and another two methods were proposed – the ‘ revised σ–w design method ’ and ‘ revised σ–ε design method ’ – for predicting the ultimate shear load of hybrid fibre or steel-fibre-reinforced self-compacting concreteT-beams. The ultimate shear load recorded experimentally was compared with the value obtained from the proposed equation. The ‘ revised σ–w design method ’ was more suitable for predicting the ultimate shear load of T-beams containing hybrid fibres and/or with stirrups, and the correlation was satisfactory.
The use of fiber reinforced polymer (FRP) materials in civil infrastructure for the repair and strengthening of reinforcedconcrete structures and also for new constructions has become common practice. The most efficient technique for improving the shear strength of deteriorated RC members is to externally bond fiber-reinforced polymer (FRP) plates or sheets . FRP composite materials have experienced a continuous increase of use in structural strengthening and repair applications around the world, in the last decade, . In addition, when the FRP was compared with steel materials, it was found that it provided unique opportunities to develop the shapes and forms to facilitate their use in construction. Although, the materials used in FRP for example, fiber and resins are relatively expensive when compared with traditional materials, noting that the crises of equipment for the installation of FRP systems are lower in cost . A review of research studies on shearstrengthening, however, revealed that experimental investigations are still needed [4, 5].
Improper planning and mass distribution on floors. Ashour, Refaie and Garrity (2004) have presented a review on Flexural strengthening of RC continuous beams using CFRP laminates. They mentioned the use retrofitting of Carbon Fibre ReinforcedComposite for enhancing the mechanical properties of RC slab on highway in China. Camata, Spacone (2007) have conducted experiments and non-linear finite element analysis of RC beams strengthened with FRP plates. They have concluded that the confinement is generally applied to members in compression, in order to enhance load bearing capacity. Esphangi, Kianoush, (2007) have studied the flexural behaviour of reinforcedconcretebeams strengthened by CFRP sheets. Garden, (1998) have conducted experimental studies on the influence of Plate End Anchorages of Carbon Fibre Composite Plates. They have concluded that retrofitting of RC structures with CFCPs strengthened the structural elements like columns, beams, slabs and walls. Hillerborg, Modeer and Peterson (1976) have analysed the crack formation and crack growth in concrete using tools like fracture mechanics and finite elements. They have based their results on the observations drawn from the demonstrations that have applied to the bending of an unreinforced beam with varying depth, by conducting tension tests.
established as an effective method applicable to many types of concrete structures such as columns, beams, slabs, and walls. Because the FRP materials are non-corrosive, non-magnetic, and resistant to various types of chemicals, they are increasingly being used for external reinforcement of existing concrete structures. From the past studies conducted it has been shown that externally bonded glass fi ber- reinforced polymers (GFRP) can be used to enhance the flexural, shear and torsional capacity of RC beams. Due to the flexible nature and ease of handling and application, combined with high tensile strength-weight ratio and stiffness, the flexible glass fiber sheets are found to behighly effective for strengthening of RC beams. The use of fiber reinforced polymers (FRPs) for the rehabilitation of existing concrete structures has grown very rapidly over the last few years. Research has shown that FRP can be used very efficiently in strengthening the concretebeams weak in flexure, shear and torsion. Unfortunately, the current Indian concrete design standards (IS Codes) do not include any provisions for the flexural, shear and torsional strengthening of structural members with FRP materials. This lack of design standards led to the formation of partnerships between the research community and industry to investigate and to promote the use of FRP in the flexural, shear and torsional rehabilitation of existing structures. FRP is a composite material generally consisting of high strength carbon, aramid, or glass fi bers in a polymeric matrix (e.g., thermosetting resin) where the fi bers are the main load carrying element.
A possible explanation for the difference between the two strengthening systems, regarding the effect of increasing the number of layers from one to two, could be found in the observed failure modes. As described in Section 3, all specimens retro ﬁ tted with FRP jackets exhibited the same failure mode which is associ- ated to the failure of the concrete substrate with no damage in the composite jackets. However, in the case of TRM-retro ﬁ tted speci- mens a change in the failure mode was witnessed when the number of layers was increased from one to two or three. In spe- ci ﬁ c, when one layer was applied the failure was attributed to local damage of the TRM jacket; the vertical ﬁ ber rovings crossing the developed shear crack at the jacket experienced a combination of partial rupture and slippage through the mortar (Fig. 9a and b). The increase in the number of layers in that case prevented these local phenomena and as a result the damage was shifted to the concrete substrate.
Increasing the shear strength of Reinforced self-compacting concrete RSCC deep beams may be required in many cases such as changing of building use, the need to perform an opening in deep beams for air conditioning, corrosion of reinforcement and finally due to construction or design errors. A very limited amount of experimental data exists on strengthening of RC deep beams in shear . Strengthening using advanced composite materials such as fiber-reinforced polymer (FRP) rods, strips or woven wraps are being increasingly recognized for enhancing flexural and shear strength of concrete members instead of the traditional materials represented by steel bars or strips [21.22]. Repair and strengthening of structural members with composite materials, such as carbon, glass, kevlar and aramid fiber-reinforced polymers, have recently received great attention [23.24]. Reduced material costs, coupled with labor savings inherent with its lightweight and comparatively simple installation, its high tensile strength, low relaxation, and immunity to corrosion, have made FRP an attractive alternative to traditional retrofitting techniques. Field applications over the last years have shown excellent performance and durability of FRP-retrofitted structures [23.24]. Nowadays, carbon and glass fiber strips, rods and wraps woven in one or multi- directions are widely used as strengthening materials.
Primer examinations were directed by Irwin (1975). Macdonald (1978) and Macdonald and Calder (1982) revealed four point stacking tests on steel plated RC beams of length 4900mm. These beams were utilized to give information to the proposed fortifying of the Quinton Bridges (Raithby, 1980 and 1982), and fused two diverse epoxy cements, two plate thicknesses of 10.0mm and 6.5mm offering width-to-thickness (b/t) proportions of 14 and 22, and a plate lap-joint at its middle. In all cases it was discovered that disappointment of the beams happened toward one side by level shear in the solid nearby the steel plate, beginning at the plate end and bringing about sudden division of the plate with the solid still joined, up to about mid-length. The outside plate was found to have a considerably more noteworthy impact regarding break control and solidness. The heaps required to cause a split width of 0.1mm were expanded by
applications in building structures such as transfer girder, wall footing, foundation pile caps, floor diaphragms e t c. For reinforcedconcretebeams with the same shear and flexural reinforcements, shear failure is most likely to occur in deep beams rather than in regular beam. Thus, retrofitting of deep beams with shear deficiencies is of great importance. A new shearstrengthening technique, designated as Embedded Through Section (ETS) technique, has been developed to retrofit existing reinforcedconcrete elements. In this technique the bars of steel or Fibre Reinforced Polymer (FRP) material are introduced into the beam section through the drilled holes and bonded with the adhesive to surrounded concrete. This paper presents the results of an experimental investigation on RC deep beams strengthened in shear using Embedded Through Section (ETS) steel bars. Three point bending tests were conducted to find the effect of ETS bar spacing and ETS bar diameter on the load carrying capacity of RC beams . The experimental results confirmed the effectiveness of ETS method; Increasing the ETS bar diameter and decreasing the ETS bar spacing resulted in a substantial increase in ultimate load .
A total of three beams were cast with the concrete grade 25 MPa in a dimension of 100 mm width x 130 mm height and 1600 mm in length. Two steel bars of diameter 10 mm were used as tension and compression reinforcement, respectively. Steel bars of diameter 6 mm with spacing 300 mm centre to centre were used as the shear links. The fibers were washed with running water at room temperature in order to remove the impurities in the fibers. After washing, the fibers were dried in oven at 70 ºC for 24 hours.
Debonding due to shear flow can be prevented by using shear connector or epoxy resin adhesive. These can be calculated by using conventional shear flow theory. Conclusion: Strengthening of reinforcedconcrete beam is one of the important tasks normally associated with on the maintenance of concrete structures. The load carrying capacity of the strengthened beams will increase if monolithicor conjugate action exists betweenthe existing beams and the strengthening materials. The monolithic action will be achieved by using either chemical bonding materials (epoxy resin adhesive etc.) or mechanical shear connectors at the interface between the strengthening materials and the existing beam and with proper end anchorage. For this purpose different types of strengthening materials are available such as sprayed concrete, steel plate, fibre reinforced polymer (FRP) and ferrocement. In general plating methods of steel plate and FRP are more preferable due to several advantages such aseasy construction work,minimum change in the overall size ofthe structure afterplate bonding and lessdisruption to traffic while the strengthening is being carried out. However,premature plate end debonding seems to be the major problems of this plating method which can be prevented by using proper end anchorages.One of the current interests in the field of strengthening is strengthening of reinforcedconcretebeams for repeated loading condition. This is required for structures such as bridges, offshore structures.
In civil engineering, there are three types of fibres commonly used; glass, carbon and aramid. The fibre component consists of fine thread-like natural or synthetic material characterized by its aspect ratio (fibre length divided by fibre diameter) and width length nearly 100 times its diameter (Cusson & Xi, 2002). Glass fibres are produced by extruding molten mass through an orifice of 0.79-3.18mm in diameter followed by drawing through fine opening of 3-20µm in diameter (ACI Committee 440, 2006). Glass fibres are commercially available in E-glass formulation (for electrical grade), the most widely used general purpose form of composite reinforcement and other formulations for high strength (S-2 glass), improved acid resistance (ECR glass) and alkali resistance (AR glass) (ACI Committee 440, 2006). The advantage of glass compared to carbon and aramid is it is a good impact-resistant fibre. However, glass is denser than carbon and aramid. The end product of glass fibre is a good electrical and thermal insulation materials. Apart from that, glass fibre is also used for radar antenna applications due to its characteristic which is transparent to radio frequency (ACI Committee 440, 2006).
The use of fiber reinforced polymer (FRP) materials in civil infrastructure for the repair and strengthening of reinforcedconcrete structures and also for new constructions has become common practice. The most efficient technique for improving the shear strength of deteriorated RC members is to externally bond fiber reinforced polymer (FRP) plates or sheets. External plate bonding is a method of strengthening which involves adhering additional reinforcement to the external faces of a structural member. The success of this technique relies heavily on the physical properties of the material used and on the quality of the adhesive, generally an epoxy resin, which is used to transfer the stresses between the flexural element and the attached reinforcement. The major constituents of FRP are the fiber and the resin. The mechanical properties of FRP are controlled by the type of fiber and durability characteristics are affected by the type of resin. FRP can be applied for strengthening a variety of structural members like beams, columns, slabs and masonry walls. Beams and slabs may be strengthened in flexure by bonding FRP strips at the soffit portion along the axis of bending. Shearstrengthening of beams may be achieved by bonding vertical or inclined strips of FRP at the side faces of beams.
Concrete is the most common material for construction. The demand for concrete as a construction material l eads t o the increase of demand for Portland cement. Concrete is known as a significant contributor to the emission of greenhouse gases. The cement industry is the second largest producer of the greenhouse gas. The environmental problems caused by cement production can be reduced by finding an alternate material. One of potential material to substitute for conventional concrete is geopolymer concrete. Geopolymer concrete is an inorganic alumino-silicate polymer synthesized from predominantly silicon, aluminium and by product materials such as fly ash, GGBS (ground granulated blast furnace slag). Geopolymer concrete does not contain cement. Hybrid fibres were used in this study. Hybrid fibre is the combination of steel fibre and basalt fibre with different volume fractions. When these fibres are added to this special concrete it improves the ductile behaviour and energy absorption capacity. This is due to the property of steel and basalt fibre to bridge the crack development inside the concrete. The main objective of the study is to look into the shear behaviour of hybrid fibre reinforced geopolymer concretebeams.