It is well known that the bond between concrete and CFRP is not stiff and due to shear strains external reinforcement may slip (Chen, Pan 2006; Pham, Al-Mahaidi 2007; Perera et al. 2004; Ueda, Jianguo 2005; Camli, Binici 2007; Lu et al. 2006; Casas, Pascual 2007; Schilde, Seim 2007; Iovinella et al. 2013; Ferracuti et al. 2007; Subramaniam et al. 2007; Mostofinejad, Shameli 2013; Wang et al. 2007; Freddi, Savoia 2008; Biolzi et al. 2013; Yuan et al. 2004; Ramos et al. 2004; Dai et al. 2005; Ramos et al. 2006; Pan, Leung 2007a; Saxena et al. 2008; Niu, Wu 2006; Pham et al. 2006; Pan, Leung 2007b; Ferrier et al. 2006; Mazzotti et al. 2008). So the deflection of the strengthened structure increases and the effect of strengthening decreases. The bond between concrete and CFRP is influenced by a few factors such as dimensions of concrete structure and CFRP, properties of the materials, and the way of anchoring external reinforcement. Only integrated performance of CFRP and strengthened structure can ensure effective strengthening. This can be reached by using additional anchoring of external reinforcement.
Abstract The objective of this study is to investigate the effectiveness of externally bonded CFRP sheets to increase the flexural strength of reinforced high strength concrete (HSC) beams. Four-point bending flexural tests to complete failure on six concretebeams, strengthened with different layouts of CFRP sheets were conducted. Three-dimensional nonlinear finite element (FE) models were adopted by ANSYS to examine the behavior of the test beams. More specifically, the strength and ductility of the beams is investigated, as the number of FRP layers and tensile reinforcement bar ratio changed. With the exception of the control beam, one to four layers of CFRP were applied to the specimens. The ductility characteristics of the test beams were evaluated in terms of the displacement, curvature and energy ductility index. It was found that for all the reported beams, the energy ductility value is about two times higher than the displacement ductility values. The crack patterns in the beams are also presented. The load deflection plots obtained from numerical study show good agreement with the experimental results.
Fiber-reinforced polymer (FRP) composite materials have been developed into economically and structurally viable construction materials for buildings and bridges over the last 25 years. They have been used in structural engineering in a variety of forms such as structural profiles, internal reinforcing bars for concrete members, strips and sheets for external strengthening of concrete and other structures. Externally bonded FRP composites are an increasingly adopted technology for the renewal of existing concrete structures [1-3]. For further use of such materials, a design code is needed that considers the inherent material variability of the FRP, as well as the variations introduced during field fabricate and environmental exposure while they are in service. There are several current guidelines for the use of FRP for strengthening reinforcedconcrete structures such as: ACI , ISIS  and FIB . The first design guideline
Carbon fibre has very high tensile strength and is also very lightweight. When it bonded to the exterior of a concrete column, beam, or slab, it can add significant strength without adding weight that would increase the load on foundations and other structural members. Carbon laminate is a stiff composite plate use to enhance the flexural and moment enhancement for structure. It is available in Rolls of 100 m, 150 m, or cut to size. An unwinding reel is available upon request. Special dimension upon Request. Its elastic modulus is 260 kn/mm 2 and tensile strength is 3900 n/mm 2 .
The test set-up for the deep beams is illustrated in Figure 3. All tested beams were loaded under three-point bending and supported as simply by two steel rollers located 200 mm from each end of the beams, which having various shear span to depth ratios of 0.8, 1 and 1.2. Steel bearing plates of 20 mm thick and 75 mm width were used and inserted between deep beam model and roller of testing machine to prevent the bearing failure at the supports. Another steel plate of 20 mm thick and 150 mm width was placed under the piston of the hydraulic jack at the loading location. The load was applied using a universal hydraulic machine with a maximum capacity of 3000kN. Mid-span deflection of the beams was measured by dial gauge.
The force-deflection relationships for the series of tested beams are depicted in Figure 13, and the main results are presented in Table V. It is observed that a double amount of the ultimate load of the corresponding reference beam was practically achieved. The increase on the load at the onset of yielding the steel reinforcement (yielding load) was also significant, varying from 32% to 47%. The displacement corresponding yielding and ultimate loads showed a minimum decrease of 45% and 47%, respectively regarding control beams. All the tested strengthenedbeams showed higher stiffness than their corresponding reference beams. The ultimate load for the strengthenedbeams was also increased attaining a maximum increase of 250%.
Abstract -This paper is focused on the nonlinear finite element analysis of the reinforced high strength concrete continuous beam strength with carbon fiber reinforced polymer sheet. Three full scale continuous beams are analyzed under two points load; the data of analysis are compared with the experimental data provided by Akbarzadeh and Maghsoudi . ANSYS V.11 program is used in FE analysis, the results obtained from analysis give good agreement with experimental result when compared load-deflection responses, ultimate strength, and the crack patterns. The results showed that with increasing the number of layers, the ultimate strength of beams are increase by amount reached (14%) for each layer. The failure mode different by increasing number of CFRP sheet layers when the beam strengthened by one layer of CFRP sheet failed by tensile rupture of CFRP sheet, and beam strengthened by more than one layer failed by intermediate crack (IC) debonding of CFRP sheet.
38 In this study, the twisting moment was applied through reversed point loads bending moment developed in the test span. Fiber orientations ±45 and 0/90 degrees were used. The CFRP material properties were the same as what was previously used by Norris et al. (1997). The thickness, 1mm/layer, was obtained from the Theoretical Moment Resistance by Andre (1995). In this study, concrete was modelled by a three dimensional (3D) structural RC Solid element, Solid65 (a finite element parameter). This element has eight nodes with three translational degrees of freedom at each node which made it capable of cracking in tension zones and crushing in compression zones. This element treated non- linearity in material properties very well. The reinforcements, on the other hand, were modelled by Link8 (a type of element used in FEA for modelling reinforcing bars), a 3D Spar element with eight nodes for which each node has three translational degrees of freedom. And for the FRP sheets, the Solid46 (a type of element used in FEA) was used to model them. The bond between steel reinforcements and concrete was assumed to be perfect with no bond loss (Kachlakev 2001; Fanning 2001) by connecting the Link8 and the Solid 65 elements at their nodes. Same concept was used for the bonding of CFRP with concrete. The program results closely follow the experimental results reported by Gesund (1964). The results show excellent conformance between the experimental and the analytical works as soon as the cracking stage in concrete started, as shown in the accompanying curve. For retrofitted RC beams, this was very interesting because the FRP effectively contributed to the strength after cracks began to form. Load-deflection curves of different twisting-to-bending moment ratios show that CFRP wrapping did not
section to cross sectional area of steel web) of 0.48 and 0.72. The requirements for applying CFRP on both or one side of web have been discussed. The ratio 0.48 is generated by using two strips of CFRP, and the ratio 0.72 is generated by using three e was surrounded by two stiffeners. The ratio of web height to shear span was 1.54 and web slenderness (web height to its thickness) was 19.7. The experimental work was consisted of five specimens. The first specimen was not strengthened. The ird specimens were strengthened by using CFRP strips on both sides of the web using CFRP ratio of 0.72 and 0.48, respectively. The fourth and the fifth specimens were strengthened by using CFRP strips only on one side of the web with CFRP ratio of 0.72 and 0.48, respectively. The experimental results revealed that using CFRP strips on the web as shear reinforcement of steel I- beams was a successful method for increasing the load capacity and decreasing the steel beam deformations. Two erved for the CFRP strips. The first failure mode was the longitudinal delamination of the CFRP strips which was more critical towards the point loads. The second failure mode was the debonding of the strips. It was also noted that, applying CFRP on the web decreased the vertical deflection of the beam, especially in the plastic region. The CFRP ratios of 0.72 and 0.48 on both sides of the web produced the same increment of load
Abstract: This paper presents an experimental investigation of flexural strength of pretensioned prestressed concretebeams with openings and strengthened with (CFRP) sheets, tested as simply supported span subjected under two-point loading. The experimental work includes testing of nine prestressed concretebeams specimens with dimensions (effective length 1800mm × depth 300mm × width 130mm), two of which were without openings as a control beams (one without and the other with strengthening by CFRP), three were with openings, and the remaining four with openings and strengthened with CFRP sheets. The opening was made at square shape (100×100) mm in flexure zone at mid span of beam. Several design parameters were varied such as: opening width, opening depth and strengthening of openings of beams by CFRP sheets at compression and tension zone. Experimental results showed that the presence of square opening (with ratio h/H= 0.333) and rectangular opening (with ratio h/H from 0.333-0.5) at mid span of beams decreased the ultimate load about (5.5)% and (5.5-33.1)% respectively when compared with beam without openings (control beam). The externally strengthened prestressed concretebeams with bonded CFRP sheets showed a significant increase at the ultimate load, this increase was about (10.9-28.8)% for flexure beams when compared with the unstrengthened beams. Moreover, the load-deflection curves for flexure beamsstrengthened with CFRP sheets were stiffer than the unstrengthened beams. Therefore, this results gave a good indication about using CFRP sheets in improvement of deflection.
Due to the presence of the CFRP plates, the stiffness of B1-RO was significantly increased in comparison with un-strengthened specimen B0. B1-RO exhibited a fairly linear trend up to a load of approximately 435 kN. Beyond this load level, there was evidence of the onset of plastic hinge formation in the top flange near the end of the CFRP plate. This is corroborated by the strain gauge output from FS1 (Figure 11a), which suggests onset of steel yielding (2000 microstrain), assuming strain compatibility between the CFRP and the steel. Lateral torsional buckling of the section between the central lateral restraints was observed to start at around 470 kN. At this point, debonding of the CFRP commenced in the top flange at the extreme edge away from the opening. Strain gauges FS2, 3 and 4 all recorded comparatively low strains indicating the CFRP strengthening in these locations was not working hard. The test was continued until a load level of 488kN, beyond this point the test was stopped due to excessive lateral deflection. The final deflected shape of the beam, including the plastic hinge location is shown in Figure 8b.The strain rosette readings from SS1 indicate that yielding did not take place in the web, Figure 12a.
and verified to have higher sensitivity than existing algorithms . Carbon Fibre Reinforced Polymer (CFRP) is fast becoming an extensively used material for externally bonded strengthening and repair of ReinforcedConcrete (RC) structures. Recent years have seen many researchers using Fibre Reinforced Polymer (FRP) sheets to strengthen and repair RC structures, accompanied by the examination of the parameters affecting the performance of the RC structure when strengthened and repaired with FRP material. Studies
The effect of the strengthening system on the post-elastic behavior of the beams was significant. Applying one, three and five layers of CFRP reduced the strain in the tension flange of the steel beam by 21 percent, 39 percent and 53 percent respectively as compared to the calculated strain in the tension flange of an unstrengthened steel beam at the same load level of 350 kN. As a result, the inelastic deformation of the beams and the measured residual deflections upon unloading were reduced. Increasing the number of layers of CFRP resulted in a decrease in the residual deflection upon unloading of the three different beams at equivalent load levels. This demonstrates that the use of externally bonded CFRP can reduce the permanent damage experienced by a structure subjected to overloading conditions. It should be noted, however, that due to the low modulus of elasticity of the CFRP large amounts of strengthening would be required to significantly reduce the residual deflections and the use of high modulus CFRP would be more efficient in this regard. Upon reloading the elastic stiffness’ of the beams were within 10 percent of their initial values. Hysteresis effects upon unloading and reloading were minimal.
Aslan 100 CFRP and GFRP rebars were used for the main flexural reinforcement of the beams and slabs. The surface treatment of these rebars is characterized by helically over-wound fibres and sand coating. The tensile properties were obtained by testing a representative number of samples in uni-axial tension, using resin filled steel tubes in the grips, and are shown in Table 1. Most of the bars failed away from the grips, so the results reflect the tensile strength of the composite. It should be noted that the strength of the larger diameter GRFP bars was similar to the strength of the smaller diameter bars, contrary to the manufacturer's supplied data. The steel rebars had a nominal diameter of 12 mm and a mean yield strength of 590 MPa and mean ultimate strength of 675 MPa.
In order to improve the structural performance of beams with openings, strengthening technique is introduced as it more economical and sustainable than reconstruction (Truog et al., 2017). There are many materials that can be used to strengthen concretebeams such as Carbon Fiber Reinforced Polymer (CFRP) laminates and plates (Salleh et al., 2017), Textile ReinforcedConcrete (TRC) wraps and steel pipes (Hauhuar et al., 2017; Jamellodin et al., 2016; Jamellodin et al., 2016). The application of CFRP to strengthen beams with large circular and square openings has been studied intensively (Chin et al., 2011; Chin et al., 2012). It was found that strengthening the opening at the flexure zone of beams significantly increased beam strength and reduced deflection and cracks compared to unstrengthened beams.
This study was aimed at increasing our understanding of the behaviour of the bond between the steel bar and the concrete along the lap splice region for structures subjected to cyclic loading. An additional aim of the study was to investigate the effect of fatigue loading on the bond between concrete and steel, and the ability of the new high and low modulus fiber- reinforced polymer (FRP) sheets to enhance the fatigue performance of a tension lap splice. Fifty three beams were cast and tested under monotonic and fatigue loading. The beams dimensions were 2200 mm in length, 350 mm in height and 250 mm in width. Each beam was reinforced with two 20M bars lap spliced in the constant moment region of the tension zone and two 10M bars in the compression zone outside the constant moment region. The test variables were the concrete cover, the presence or absence of FRP wrapping, the type of the FRP wrapping glass or carbon fiber-reinforced polymer (GFRP or CFRP), the type of loading and the fatigue load range. The minimum load applied was 10% of the static bond capacity of the specimen. The maximum load was varied to obtain fatigue lives between 1,000 and 1,000,000 cycles. The test frequency for all cyclic tests was 1.3 Hz.
McCurry 2000). Raghu et al. (2000) aimed at increasing the shear strength of reinforcedconcretebeams with T cross- section using carbon FRPs in the study they performed. For this purpose, they applied GFRP plates on all beam surfaces with and without anchorage (Raghu et al. 2000). Li et al. (2001) tested the beams with insufﬁcient shear reinforce- ment in the study they performed. The effect of the amount of GFRP used to strengthenedbeams on beam shear strength was researched (Li et al. 2001). Ali et al. (2001) studied on separation mechanisms in the reinforcement of the beams in terms of bending and shear in the study they performed. In the study, the steel plates used for reinforcement and FRP plates were compared (Ali et al. 2001). Khalifa and Nanni (2000) increased the shear strength of beams with a rectan- gular cross-section using GFRP plate in the study they per- formed. Diagana et al. (2003) aimed at reinforcing rectangular beams with insufﬁcient shear reinforcement against shear in the study they performed. GFRP plate was adhered on the surface of tested beams in 4 different forms. GFRP plates were adhered as perpendicular and 45° to the horizontal (Diagana et al. 2003). Wegian and Abdalla (2006) strength- ened beams against shear in the study they performed. GFRP, CFRP, and FRP were used on the specimens tested in the study (Wegian and Abdalla 2006). Riyadh and Riadh (2006) aimed at reinforcing the reinforcedconcretebeams against shear and bending with GFRP plates in the study they per- formed. Anıl (2006) studied on strengthening of reinforcedconcretebeams against shear using GFRP plates. GFRP plate width and method of application of plates were determined as experiment parameters (Anıl 2006). Bencardino et al. (2007) strengthenedbeams without shear reinforcement against shear using GFRP in the study they performed. Kang et al. (2014) used carbon ﬁbers (CF) and glass ﬁbers (GF) combined to strengthen concrete ﬂexural members. In their study, data of tensile tests of 94 hybrid carbon-glass FRP sheets and 47 carbon and GF rovings or sheets were thoroughly investigated in terms of tensile behavior (Kang et al. 2014). Kang and Ary (2012) used ﬁber-reinforced polymers (FRP) to enhance the behavior of structural components in either shear or ﬂexure. The research focused on the shear-strengthening of reinforced and pre-stressed concrete (PC) beams using FRP (Kang and Ary 2012). Ary and Kang (2012) experimentally evaluated the impact of carbon ﬁber-reinforced polymers (CFRP) amount and strip spacing on the shear behavior of PC beams and evaluated the applicability of existing analytical models of FRP shear capacity of PC beams shear-strengthened with CFRP. Kang et al. (2012) reviewed the debonding failure of FRP laminates externally attached to concrete. They also discussed the inﬂuences on bond strength and failure modes as well as the existing experimental research and developed equations (Kang et al. 2012).
the centres of the beams were cut (width of 5 mm and depth of 75 mm) with an electronic saw. These saw-cuts were planned to induce debonding failure in beams because the highest tensile stress can be fully transferred to FRP. After cutting, the beams were flexurally strengthened withone or two sheets of CFRP or GFRP, the sizes of which were 130 mm in width and 300 mm in length. All the beams were tested under three-point loading with an effective span of 450 mm. Mohammed Rashwan et al. (2015) examined thesize effect of reinforcedconcretebeamsstrengthened with CFRP and GFRP sheets in flexure. Two types of FRP sheets were considered in this study; Carbon and Glass fibre reinforced polymer sheets (CFRP and GFRP). FRP sheets were bonded to the soffit of the beams using a two-part epoxy. Tara Sen and Jaganatha Reddy (2013) investigated the flexural and tensile behavior of reinforcedconcretebeamsstrengthened using natural textile jute fibre and it was compared with CFRP and GFRP strengthening systems. A total of fourteen beams were cast in three groups. Among these three groups, the first group comprised of control specimens and the other two groups were strengthened RC beams. Rami Hawileh et al. (2014) studied the behavior of reinforcedconcretebeamsstrengthened with externally bonded hybrid fibre reinforced polymer systems. The experiment consisted of casting and testing five beams of size 120X240X1840 mm. One beam served as the control beam and four beams were strengthened in flexure with GFRP, CFRP and Hybrid FRP sheets. The beams were tested under four-point bending. The results were presented in terms of observed failure modes, load versus mid-span deflection and load versus FRP strain relationship at mid-span. Thomas Kang et al. (2014) examined the hybrid effects of FRP laminates
The midspan deflection of the 450mm specimen, as presented in Figure 5.44, remained unchanged for a shorter period than the uncorroded unpatched specimen. After 20 000 cycles the specimen exhibited a significant increase in stiffness degradation rate for 10 000 cycles. After the 30 000 cycle interval the stiffness degradation rate reduced and remained consistent until the 60 000 cycle interval, which marked the commencement of another increase in stiffness degradation. Evaluation of the composite material strains also showed an increase in compression concrete strain at the 60 000 cycle mark, which suggested that one of the tension steel bars may have ruptures at this point. Ultimate failure of the section was caused by rupturing of the second tension steel bar leading to CFRP delamination and ultimately crushing of compression concrete under the left load application point at 119 716 cycles. This indicated a relatively high post-fatigue life of 49.9%. In terms of the overall stiffness degradation, the 450mm specimen was found to have the second lowest stiffness as well as the second lowest fatigue life, where the rapid high stiffness reduction rate during the 20 000 to 30 000 cycles period contributed significantly to the overall stiffness reduction. Given its early occurrence during the fatigue life of the specimen, this initial increase in stiffness reduction rate was attributed to likely bond slippage induced stress redistribution, after which the specimen stiffness deteriorated at a much higher rate than the other specimens tested under the 60% stress range regime.
A paper presents a numerical analysis using ANSYS finite element program to develop a model for expecting the performance of seven lightweight aggregate reinforcedconcrete deep beams with 28 days compressive strength 26MPa and density of 1950Kg/m 3 strengthened in shear by externally bonded CFRP. All beams have same dimensions (150mm width, 400mm depth and 1400mm length), longitudinal steel reinforcement ratio ρ=0.0115 and shear steel reinforcing 5@100mm. CFRP strips 50mm width are used for strengthening. The effective variable parameters were: a/d ratio, CFRP spacing, orientation and number of layers. The results obtained from the ANSYS finite element model got good agreement when compared to the experimental results  which were done for the same deep beams with the same material properties, internal reinforcement and strengthening schemes. The results show that the ultimate load and deflection predicted by numerical analysis is less than experimental results by 9% and 5.7% in average respectively. By using CFRP strips in shear strengthening, the ultimate load has increased by 18%, 13.6%, 32% and 27.3% for vertical, horizontal, inclined and double vertical layers, respectively for a/d=1. For a/d =0.8 the increase is 10% for vertical strips. It is recommended that the CFRP is placed such that the principal fiber orientation is either normal to the longitudinal beams axis or normal to the line joining the applied load and supports (strut path) to resist higher tensile stresses and strains distributed along it.