Over the several last decades, strengthening of existing structures including reinforcedconcretebeams, slabs, walls and columns through the externally bonded reinforcement (EBR) and the nearsurfacemounted (NSM) methods with fiber reinforced polymer (FRP) has been successfully utilized in civil engineering applications due to its efficiency, effectiveness and ease of application for strengtheningconcrete structures in both flexure and shear. A laminate or textile bond onto the surface of concrete elements in externally bonded method (EPR) while the nearsurfacemounted method consists of placing fiber reinforced polymer bars into grooves precut on the concrete members and embedding them with a high-strength adhesive . The efficiency of using FRP for strengthening of reinforced members according to the nearsurfacemounted (NSM) method is widely proven in comparison to the externally bonded reinforcement (EBR) due to the fact that, the tensile strength of fiber reinforced polymer is better exploited . Moreover, application of fiber reinforced polymer (FRP) with the nearsurfacemounted (NSM) method is an alternative to the externally bonded reinforcement technique to mitigate the risk of premature debonding failure [8, 9], deterioration of FRP materials, protection against environmental corrosion and temperature, better aesthetics, as well as delimit any imperfection accommodate to the installation procedure [10, 11]. Fracture of flexural components (FRP materials), detachment of FRP sheets from the structural elements and flaking of concrete in EBR scheme of strengthening lead an additional difficulty arising from the fact that only limited amount of FRP can be used to increase the beam flexural capacity . However, application of nearsurfacemounted technique is appropriate only if the cover of the internal reinforcement is sufficiently thick for the groove size to be accommodated . It worth mentioning that, the performance of the nearsurfacemountedbars in strengthening of existing reinforcedconcrete elements is affected by local bond slip behavior, surface characteristics of FRPbars and treatments of reinforcement and grooves, interactions of FRP rods with the surrounding materials, geometry of FRPbars, and the concrete cover [7, 13].
Aguilar, G., Matamoros, A.B., Parra-Montesinos, G.J., Ramírez, J.A. & Wight, J.K. (2004). Experimental Evaluation of Design Procedures for Shear Strength of Deep ReinforcedConcreteBeams. ACI Structural Journal. 99(4), pp. 539-548. Ali, A., & Mezher, T. (2015). Shear Strengthening of RC without Stirrups for Deep Beams with NearSurfaceMounted CFRP Rods. International Journal of
Over the past decade, research studies have been conducted on using fiber reinforcement polymers (FRP) as strengthening material to improve the performance of existing slab-column connections. FRP can be used in two methods; externally installed [1-6] and internally installed [7-10]. The FRP externally strengthened system consists of one or more FRP sheets / laminates bonded to the tension side of the slab using epoxy adhesive. This strengthening method increase the flexural reinforcement and therefore increase the punching shear strength by delaying the shear cracks formation. The common failure for external strengthening technique is the premature debonding of FRP, which could be delayed and improve the structural behavior of strengthened connection by providing end anchorage to the externally bonded FRP . Post-installation of FRP studs or FRP shear dowels, as shear reinforcement, in drilled holes filled with suitable epoxy grout falls into internal strengthened method for slab-columns connections. The drilled holes, to insert shear reinforcement, in the critical punching shear area of the slab near the column could further damage the degenerated slab. This strengthening technique is not practically the suitable solution in several situations.
would be noted that similar to the characteristic of con- ventional prestressed RC beams with strengthening materials, the RC beam strengthened with the Fe-SMA NSM technique showed an insignificant increase of the ultimate loads with higher pre-straining levels of the Fe- SMA strips. Additionally, the RC beam strengthened with the Fe-SMA NSM technique did not show a reduc- tion of ductility by introducing prestressing force to the concrete compared to the RC beam strengthened by the prestressed FRP NSM technique. Based on those results, it would seem that the prestressing technique using the recovery stress of the Fe-SMA strip can overcome the limitations of conventional strengthening techniques using prestressed FRP plates or steel strands such as difficult-to-apply pre-tension force, required equipment for anchoring, and reduced ductility of the strengthening material.
Although field applications of NSM FRPstrengthening are not as common compared to EB retrofitting, the technique has already been applied with satisfactory results. In 1999 a construction error led to the necessity of strengthening a joint between a precast concrete element and a cast in situ concrete structure on a bridge. As the zone that required strengthening was to lie directly below an asphalt pavement, FRP was considered as an alternative to steel due to its corrosion resistance, and the NSM technique over EB retrofitting for simplicity of installation and for providing a safer location for the FRP to resist the expected periodical pavement resurfacing and deck sealing works, including high temperatures when pouring asphalt. The client, The Swedish Road Authority, considered the strengthening work successful and today accepts the technique as a method of strengtheningconcrete bridges (Taljsten et al., 2003).
weight ratios are required. The use of FRP composites for the rehabilitation of beams and slabs started about 30 years ago with the pioneering research performed at the Swiss Federal Laboratories for Materials Testing and Research, or EMPA . Afterward, FRP materials have been widely used as a solution to enhance the ductility of beam members in RC structures. Because of high cost of FRP materials in the past, most applications of these materials were for rehabilitation purposes and externally bonding of members in RC structures. However, by increase of the usage of FRP materials, the costs dropped dramatically nowadays and this leads to more and more applications of these materials in constructions and rehabilitation projects in the future. Past earthquakes reconnaissance showed that beam members in some structures have performed poorly due to corrosion of steel reinforcement in concrete and probable brittle-type failures with low ductility . Where FRP composites are used as reinforcement in the reinforcedconcrete (RC) beams, they increase the strength (ultimate limit state) and the stiffness (serviceability limit state) of the structure. Structural design of beams with FRP reinforcement is thus motivated by requirements for earthquake strengthening, higher service loads, smaller deflections, or simply the need to complement deficient steel reinforcement . In the past two decades, researchers have performed various investigations to develop proper methods for designing steel reinforcedbeams that have ductile behaviour while providing high bending and shear capacity. On the other hand, many studies focused on strengthening and repairing RC beams using other methods such FRP reinforcing. Regarding the mechanical properties of the FRP reinforcement, the main differences in
Focus has increased recently on strengtheningreinforcedconcrete structures that deteriorate due to aging, corrosion of steel reinforcing bars, excessive loading, or severe environmental conditions. The strengthening of RC structures has been successfully implemented using fabric reinforced cementitious matrix (FRCM) systems for the flexure strengthening of RC beams. There is, however, a problem of premature debonding which is observed in high fabric strength FRCM systems which does not allow full utilization of the strengthening material. It has also been a problem in FRCM systems to use multiple layers for strengthening, where using more than two layers causes premature failure in the strengthened beams. This work aims to counter the problem of premature failure by investigating the relatively new concept of nearsurface embedded (NSE) strengthening where the strengthening material is embedded within the concrete cover at the soffit of the beam thus allowing the FRCM to be better utilized. Three different types of FRCM systems have been investigated, namely: Carbon, Polyparaphenylene Benzobisoxazole (PBO), and Glass. The potential of combining both NSE strengthening and the traditional externally bonded (EB) methods resulting in the hybrid nearsurface embedded/externally bonded (NSE/EB) is also examined in this work to investigate the efficient application of multiple FRCM layers in flexure. Part of the results of this work have been successfully published proving that it is a viable strengthening application .
The near-surfacemounted (NSM) is an effective technique for the shear strengthening of reinforcedconcrete (RC) elements. This technique is based on cutting of grooves in the concrete cover of the elements to be strengthened, in which steel or fiber reinforced polymer (FRP) bars are inserted and bonded to the surrounding concrete substrate using an epoxy adhesive. Externally bonded reinforcement (EBR) was the conventionally used technique for shear strengthening of RC beams; however the NSM technique showed a significant increase in shear strength which indicates its efficiency over the EBR techniques . The NSM technique can be used to enhance the flexural capacity, shear capacity and ductility of RC beams. NSM reinforcement is less prone to de-bonding failures because of their better bond performance than EBR techniques. NSM bars are less susceptible to corrosion and fire damages as they are protected by the concrete cover. It is also an aesthetically appealing technique. NSM techniques become particularly interesting in the seismic retrofit of deteriorated RC beam-column joints.
Nineteen concrete prisms were tested using a direct single-lap shear test (Figure 5.11). FRP strips were externally bonded to one face of the concrete blocks. The classical push-pull configuration was adopted where fibers were pulled while the concrete prism was restrained. The dimensions of all concrete blocks were 150 mm width × 150 mm depth × 600 mm length. The epoxy resin was used to impregnate the fiber along the entire steel-FRP strip, also outside of the bonded area. The fibers were arranged across the width of the reinforcement in order to have approximately a distance between the external fibers of the grid and the edges of the matrix equal to half of the fiber spacing. The thickness of each layer of matrix was 2 mm, thus, the total thickness of the composite strip was equal to 4 mm. The bonded area started 70 mm from the top edge (loaded end of the strip) of the concrete prism to obtain an initial interfacial notch. The FRP strips were directly gripped by the machine head. The concrete prism was restrained against movement by two steel plates placed against the square faces of the prism. The bottom square plate was bolted to a cylindrical steel element that was gripped by the bottom wedges of the testing machine. The top plate was a C-shaped steel element designed to have the centroid as close as possible to the centroid of the bottom plate, in order to reduce the undesired effects of the inherent eccentricity of the single-lap shear tests. The top plate was connected to the bottom one through four steel bars bolted to the two plates. Three strain gages, aligned with the longitudinal axis of the bar, were mounted on each steel bar, and arranged 120° apart one another. The average of the three strain measurements on each bar gives an approximate estimate of the strain along the bar, which is used to analyze the initial pre-compression load applied to the specimen prior to starting the test and evaluate the stress on each bar during the test. Direct shear tests were conducted under displacement control using a close-loop servo- hydraulic universal testing machine. Two linear variable differential transducers (LVDT) were mounted on the concretesurface close to the top edge of the bonded region. The LVDTs (named LVDT a and b) reacted off of a thin aluminum Ω-shaped plate that was attached to the epoxy surface adjacent to the beginning of the bonded area. The average of LVDT a and b is defined as the global slip g in this paper. The global slip g was increased at a constant rate. All tests were conducted at a global slip rate equal to 0.00084 mm/s. Two additional LVDTs (named LVDT c and d) were
The dual function of a carbon fibre reinforced polymer (CFRP) rod working as the nearsurfacemounted (NSM) strengthening and impressed current cathodic protection (ICCP) anode for corroded reinforcedconcrete structures has been proposed and researched. In this paper, a CFRP rod was used for both flexuralstrengthening of pre-corroded reinforcedconcretebeams and in a dual functional capacity as an ICCP anode. After a period of ICCP operation at high current density, the beams were subjected to flexural testing to determine the load-deflection relationships. The potential decays of the steel met recognised ICCP standards and the CFRP remained effective in strengthening the corroded reinforcedconcretebeams. The bonding at the CFRP rod anode and concrete interface was improved by using a combination of geopolymer and epoxy resin, therefore the ultimate strength of a dual function CFRP rod with combination of bonding medium (geopolymer and epoxy) increased significantly.
In current time in Malaysia, as the demand of steel is higher than production itself making the rule of supply and demand applies and led to the rise of its price. The steel is also has problem regarding corrosion. The usage of fiber reinforced polymer (FRP) composite for concrete applications is relatively a new technology that has a potential to replace the traditional steel reinforcement in construction industry as it has the advantages such as not subjected to corrosion, high tensile strength and low unit weight. But since the mechanical properties and surface deformation of FRPbars are different from the conventional steel reinforcement used, investigation is needed to study the behavior of structures using FRP. This study will focus on investigating the flexural behavior of beamsreinforced with FRP to see the material’s ability to resist deformation under static monotonic load.
Abstract: This paper presents an experimental work to study the ﬂexural strength of reinforcedconcrete (RC) beams strengthened by partially de-bonded nearsurface-mounted (NSM) ﬁber reinforced polymer (FRP) strip with various de-bonded length. Especially, considering high anchorage capacity at end of a FRP strip, the effect of de-bonded region at a central part was investigated. In order to check the improvement of strength or deformation capacity when the bonded surface area only increased without changing the FRP area, single and triple lines of FRP were planned. In addition, the ﬂexural strength of the RC member strengthened by a partially de-bonded NSM FRP strip was evaluated by using the existing researchers’ strength equation to predict the ﬂexural strength after retroﬁt. From the study, it was found that where de-bonded region exists in the central part of a ﬂexural member, the deformation capacity of the member is expected to be improved, because FRP strain is not to be concentrated on the center but to be extended uniformly in the de-bonded region. Where NSM FRP strips are distributed in triple lines, a relatively high strength can be exerted due to the increase of bond strength in the anchorage.
High-performance materials that include advanced composites can have very high strength-to-weight ratios and are suitable for efficient structural repair of deficient members. These materials allow for rapid placement and require minimal labour compared to traditional methods. The use of fiber-reinforced polymer (FRP) laminates and fabrics to repair and strengthen reinforcedconcrete (RC) structures is well established, with design guidelines in the form of ACI 440.2R-08 (ACI Committee 440, 2008), Technical Report 55 (Concrete Society, 2012), and European fib bulletin 14 (Fe´de´ration internationale du be´ton ( fib) Task Group 9.3, 2001). Over the past decade, carbon fiber– reinforced polymer (CFRP) composites have proven to be a cost-effective and successful retrofit method for buildings and bridges. The primary advantages they offer over other materials include their noncorrosive properties, magnetic transparency, high strength, low weight, high durability, and ease of application. Many bridges around the world have been repaired and/orFibre reinforced plastic (FRP) reinforcement plays a very important role in the retrofitting and rehabilitation of reinforcedconcrete (RC) structural elements as an external and nearsurface reinforcements. Recent developments in these fields have a wide range of application. Several investigators carried out experimental or theoretical investigations on concretebeams and columns retrofitted with carbon/glass fibre reinforced polymer
FRP has been used in different configurations and techniques to make use of the material e ffective ly and to ensure long servi ce life of the selected system. One of these innovative strengthening techniques is the near-surface mounting (NSM) technique which consists of placing FRP re inforc ing bars or strips into grooves precut into the concrete cover in the tension zone of t he strengthened concrete me mber and bonded to the three sides of the groove using high -strength epoxy adhesive or cementit io us grout. This method is relat ively simp le and here, the grid considerably enhances the bond of the mountedFRP reinforce ments, thereby using the material mo re effectively. Configuration of the FRP re inforce ments used for th e NSM technique is controlled by the depth of the concrete cover. After installation, the NSM -FRP re inforce ments are protected against mechanical da mage, wear, impact, and vandalism fro m vehic les  . The technique could also provide better fire resistance in the event of a fire a nd therefore, it could reduce the cost of fire protection measures.
After the completion of a comprehensive literature review, there has been no significant studies found which cover the use of ECC as an adhesive in a NSM system to strengthen existing concrete or masonry structures. As such there is an opportunity to complete some unique research which may lead to the identification of suitable application for ECC. One similar study by Afefy et al (Afefy & Mahmoud 2014) was found which was similar. In Afefy’s precast ECC strips were cast into the tension cover zone of a reinforcedconcrete girder during fabrication of the girder, this is dissimilar to a typical NSM system in that it is not a retrofitted system. However the arrangement of the system is similar in that it replaces concrete with a material which would perform better than concrete when loaded in tension. Afefy’s research was able to demonstrate that the ECC strips lead to improved performance of the affected girders in regard to both serviceability and strength.
Near-surfacemounted (NSM) fiber-reinforced polymer (FRP) reinforcement is a latest and most promising strengthening techniques for reinforcedconcrete (RC) structures. Issues raised by the use of NSM FRP reinforcement include the optimization of construction details, models for the bond behavior between NSM FRP and concrete, reliable design methods for flexural and shear strengthening. In line with this, a very important issue in the manufacture of composites is the selection of the optimum matrix (Resins) because the physical and thermal properties of the matrix significantly affect the final mechanical properties as well as the manufacturing process. In order to be able to exploit the full strength of the fibers, the matrix should be able to develop higher ultimate strain than the fibers. The matrix not only coats the fibers and protects them from mechanical abrasion and chemical attack, but also transfers stresses between the fibers .
The beams strengthened with 10 mm and 12 mm diameter bars showed an increase in load carrying capacity by 4.87 % and 7.31 % respectively when compared with control beam specimen. BD10G20 failed under flexure and no debonding failure at polyester–concrete interface or at bar polyester interface occurred and also cracking of polyester resin grout also did not occur. Similarly in the case of BD12G20 failed under flexure and cracking of polyester resin grout also did not occur whereas a slight debonding failure at polyester– concrete interface occurred near to the supports as shown in Fig -8. Due to this the increase in load carrying capacity of the beam BD12G20 is only 2.44 %. Table -4 shows the ultimate load carrying and the percentage increase in load carrying capacity.
Abstract: This paper reports and compares experimental studies on flexural performance of concretebeamsreinforced with hybrid fiber reinforced polymer (FRP) and steel HRB bars with this study and other literatures. The objective of this study is to examine the effect of hybrid FRPs on structural behavior of retrofitted RC beams and to investigate if different sequences of BFRP and GFRP bars of the hybrid FRPs have influences on improvement of strengthening RC beams, Total 3 steel reinforcedconcretebeams and 8 hybrid reinforcedbeams were designed using only HRB steel bars and hybrid G/BFRP-steel bars respectively. The flexural bearing capacity, the maximum crack width and the deflection of the test beams were obtained and analyzed. Results show that the ultimate bending moment of hybrid reinforced is slightly less than that of steel reinforcedconcrete beam with the same reinforcement ratio. It can be concluded that it is feasible to replace the corner steel bars of concrete members with FRPbars without reducing the flexural bearing capacity. However, the deflection and maximum crack of hybrid reinforcedconcretebeams are much higher than those of steel reinforcedconcretebeams at the same load levels. The theoretical calculation method can effectively predict the flexural bearing capacity, crack spacing, maximum crack width and deflection of hybrid reinforcedconcretebeams, which can be used in engineering design reference.
This paper presents an analytical study to verify the ACI 549-4R-16 code for experimentally tested ReinforcedConcrete (RC) beams, which were strengthened to enhance the flexural capacity using Fiber-Reinforced Cementitious Mortars (FRCM). Twelve RC beam specimens having 2500 mm length, 150 mm width, and 260 mm depth were prepared with two different reinforcement ratios (ρ_s^D12=0.72% and ρ_ s^D16=1.27%), and were then strengthened with two different FRCM systems, namely carbon and polyparaphenylene-benzobisoxazole (PBO) FRCM systems. Two RC beams were tested as control specimens. Six beams were externally reinforced using single, double and triple layers of carbon FRCM system, while the remaining four beams were repaired with one and two layers of PBO FRCM system. The strengthened RC beams were tested in flexural under four-point monotonic loading. The experimental results revealed that a reasonable gain in flexural strength was achieved for both FRCM systems, with up to 78% increase in flexural capacity for carbon FRCM systems and up to 27.5% for PBO FRCM system over that of their control specimens. Further, the results obtained from the theoretical approach using the ACI 549 code conform well with the experimental load- carrying capacities. Moreover, the values obtained for experimental to theoretical ratio are quite close to 1.00 which somewhat shows satisfactory computational results. Keywords: Fabric-reinforced cementitious mortar; Flexuralstrengthening; Reinforcedconcretebeams; Reinforcement ratios; FRCM systems
All beams strengthened with SB or UW FRP jackets failed in shear at an ultimate load substantially higher than that of the control beam; thus con ﬁ rming the effectiveness of FRP jacketing in shear strengthening of RC members. The peak load attained by specimens SB_R1, UW_R1, SB_R2 and UW_R2 was 105, 113.4, 124.5 and 126.2 kN, respectevily, which yields 103%, 119%, 140% and 143% increase in the shear capacity, respectively. In all these specimens failure occurred due to FRP debonding; the excellent bond between the resin and the concrete substrate resulted in peeling off of the FRP jackets with part of the concrete. It was observed that in specimens with SB jackets the part of concrete that peeled off was thinner with respect to the specimens with UW jackets (Fig. 8a and Fig. 8b). Debonding of FRP reinforcement was initiated from the point of load application and propagated instantly to the support (Fig. 8c). One layer of FW FRP jacket resulted in enhancing at least 2.8 times the shear capacity. Specimen FW_R1 reached its ultimate moment capacity at a load of 150.3 kN and failed due to concrete crushing after yielding of the tensile longitudinal reinforcement (at approximately 140 kN e Fig. 8d). This con ﬁ rmed the high effec- tiveness of closed FRP jackets. However, the use of closed jackets is not feasible in beams of typical RC buildings or bridge girders due to the presence of concrete slabs or decks, respectively.