The failure modes of reinforced concrete (RC) beamsstrengthened in shear with fiber reinforced polymer (FRP) sheets or strips are not well understood as much as those of RCbeams reinforced with steel stirrups. When the beams are strengthened in shear with FRP composites, beams may fail due to crushing of the concrete before the FRP reaches its rupture strain. Therefore, the effectivestrain of the FRP plays an important role in predicting the shear strength of such beams. This paper presents the results of an analytical and experimental study on the performance of reinforced concrete beamsstrengthened in shear with FRP composites and internally reinforced with conventional steel stirrups. Ten RCbeamsstrengthened with varying FRP reinforcement ratio, the type of fiber material (carbon or glass) and configuration (continuous sheets or strips) were tested. Comparisons between the observed and calculated effective strains of the FRP in the tested beams failing in shear showed reasonable agreement.
The first study in shear strengthening of RCbeams with FRP was performed by Berset . He tested some RCbeams in both of control specimens and FRP-strengthened specimens type and developed a simple analytical model for shear contribution of FRP composite, which in this model, FRP treated similar to steel stirrups. Uji  tested RCbeamsstrengthened by FRP with bonding FRP on their side faces either vertical or inclined. In this study, Uji focused on debonding shear stress. In another work, Veilhaber and Limberger  tested some large scale RCbeams, and the test results indicated that even small amounts of external reinforcement could avoid brittle shear failure. Chajes et al.  tested 12 beams, four as control specimens and eight as strengthenedRCbeams with aramid, E-glass, and graphite fibers. The tests results indicated that FRP composite increases in the ultimate strength of about 60 to 150 percent. Sato et al.  tested some
Abstract. One of the most common options for structural strengthening and rehabil- itation is the use of FRP sheets for shear-torsion strengthening of Reinforced Concrete Beams (RCBs). Their widespread use owes much to their ease of application in addition to many other advantages. The availability of technical references and construction codes today makes it easy to calculate the shear and torsion capacities of strengthenedbeams. Practically, however, it is combined shear and torsion rather than pure torsion that develops in beams. The present article investigates the use of FRP sheets in strengthening RCbeams. For the purposes of this study, 14 RCbeams were used that were classied into three dierent sets: one set consisted of 5 non-strengthened (plain) beams and two sets (one with 5 and the other with 4 beams) consisted of RCbeamsstrengthened with CFRP sheets in two dierent strengthening patterns. The shear-torsion interaction curves were derived for them by loading the beams under a variety of eccentricities ranging from 0 (pure shear) to innity (pure torsion). The supports were constructed with exure and torsion rigidity. Laboratory tests revealed that the shear-torsion interaction curves for all the three sets of beams were close to straight lines.
 Alex L., Assih J., and Delmas Y. (2001), “Shear Strengthening of RCBeams with externally bonded CFRP sheets”, Journal of Structural Engineering, Vol. 127, No. 4, Paper No. 20516.  Balamuralikrishnan R., and Jeyasehar C. A. (2009), “Flexural behaviour of RCbeamsstrengthened with Carbon Fiber Reinforced Polymer (CFRP) fabrics”, The Open Civil Engineering Journal, 3, 102-109.
UHPC strengthening system is an alternative approach to rehabilitate or restore the deteriorated concrete mem- bers or to retrofit or strengthen the sound concrete members. It has exceptional advantages over traditional methods such as steel plate-bonding (Altin et al. 2005), fiber reinforced polymer (FRP) strengthening (Chen and Teng 2003), section enlargement, etc. For example, FRP possesses desired properties such as high strength, corro- sion resistance, ease to apply, and without much change in the size of the structural member. However, FRP sys- tem has some shortcomings, which are mainly related to bonding, compatibility and fire-resistance problems. On the other hand, UHPC can be used as a strengthen- ing material for existing structures having either sound or deteriorated concrete surfaces. Therefore, for repair- ing or rehabilitating of concrete structures, UHPC can be considered as a good option which can enhance the structural performance and durability of substrate con- crete (Li 2004).
onto wet surfaces or in low temperatures, low fire resistance, low glass transition temperature, and lack of vapor permeability, which are associated with the use of organic matrix, have prompted the development of new innovative composite strengthening materials. One promising material is fiber reinforced cementitious matrix (FRCM) composites. FRCM composites avoid the toxicity of the epoxy resin and overcome some of the aforementioned limitations of using FRP strengthening material. FRCM composite material is comprised of continuous fibers in an inorganic mortar matrix that is more compatible with concrete and masonry substrates, can be applied onto wet surfaces, and has better heat resistance than FRP composites. Because the matrix is a mortar, the resulting thickness of FRCM composites is generally larger than that of FRP composites (on the order of 5 times). Different types of fibers including carbon, glass, aramid, basalt, steel, and polyparaphenylene benzobisoxazole ( PBO) have been used in FRCM composites. FRCM composites have been studied for flexural strengthening [e.g., 19- 23], shear strengthening [e.g., 24-28], and confinement applications [e.g., 29-30] for RC members, but studies in the technical literature on their use for torsional strengthening are extremely limited .
The use of fiber reinforced polymer (FRP) as a strengthening material is one of the applied strengthening techniques of reinforced concrete beams. This results from a number of advantages, such as excellent strength to self-weight ratio, high tensile strength, large fatigue resistance capacity, and high durability,  and . Reinforced concrete (RC) beamsstrengthened with carbon and glass fiber-reinforced polymer (CFRP and GFRP) composites introduces a promising solution to improve shear and flexural capacities and ductility, as well as altering the mode of rupture, [3-6].
Siddiqui (2009) has studied the experimental investigation of RCbeamsstrengthened with externally bonded fiber reinforced polymer (FRP) composites. Use of externally bonded FRP sheets/strips/plates is a modern and convenient way for strengthening of RCbeams. Although in the past substantial research has been conducted on FRPstrengthenedRCbeams, but the behaviour of FRPstrengthenedbeams under different schemes of strengthening is not well established. In this study, practical FRP schemes for flexure and shear strengthening of RCbeams has been studied. For this purpose, 6 RCbeams were cast in two groups, each group containing 3 beams. The specimens of first group were designed to be weak in flexure and strong in shear, whereas specimens of second group were designed just in an opposite manner i.e. they were made weak in shear and strong in flexure. In each group, out of the three beams, one beam was taken as a control specimen and the remaining two beams were strengthened using two different carbon fiber reinforced polymer (CFRP) strengthening schemes. All the beams of two groups were tested under similar loading. The response of control and strengthenedbeams 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 faces of RCbeams are very effective in improving the shear capacity of beams. He concluded that for shear strengthening, externally bonded inclined CFRP-strips show a far better performance than vertical CFRP-strips as specimen strengthened using inclined strips gives higher shear and deformation capacity than specimen strengthened using vertical strips. Also the inclined CFRP-strips arrest the propagating cracks more effectively than the vertical CFRP-strips.
Abstract: Transverse reinforcement plays a key role in the response behavior of reinforced concrete beams. Therefore, corrosion of steel stirrups may change the failure mode of elements from bending to shear, leading to a brittle and catastrophic crisis. It is important to strengthen reinforced concrete beams with corroded stirrups to enhance the shear resistance. This paper presents a formulation, based on the modified compression field theory, to estimate the ultimate shear of reinforced concrete beamsstrengthened with FRP, because of stirrup corrosion. The detrimental effect of corrosion on steel stirrup yield strength was taken into account by introducing an empirical decay law. The effectivestrain of FRP reinforcement was adequately evaluated by considering both debonding and tensile stress rupture. The proposed model was validated against collected experimental results, showing a good ability to evaluate shear strength. Moreover, a numerical analysis was carried out to highlight the role of the key parameters predicting the ultimate shear.
Abstract: Numerous investigations of RCbeamsstrengthened in shear with externally-bonded (EB) ﬁbre-reinforced polymer (FRP) sheets, plates and strips have been successfully conducted in recent years. These valuable studies have highlighted a number of inﬂuencing parameters that are not captured by the design guidelines. The objective of this study was: (1) to highlight experimentally and analytically the inﬂuential parameters on the shear contribution of FRP to RCbeamsstrengthened in shear using EB FRP sheets and strips; and (2) to develop a set of transparent, coherent, and evolutionary design equations to calculate the shear resistance of RCbeamsstrengthened in shear. In the experimental part of this study, 12 tests were performed on 4,520-mm- long T-beams. The specimens were strengthened in shear using carbon FRP (CFRP) strips and sheets. The test variables were: (1) the presence or absence of internal transverse-steel reinforcement; (2) use of FRP sheets versus FRP strips; and (3) the axial rigidity of the EB FRP reinforcement. In the analytical part of this study, new design equations were proposed to consider the effect of transverse-steel in addition to other inﬂuential parameters on the shear contribution of FRP. The accuracy of the proposed equations has been veriﬁed in this study by predicting the FRPshear contribution of experimentally tested RCbeams.
All beams were tested in a four-point bending, because it gives constant maximum moment and zero shear in the section between the loads. The loading was applied as dis- placement-controlled monotonic or quasi-static cyclic load- ing history by a reversible two-point loading system located at 275 mm on either sides of the mid-span. Monotonic loading was applied with a constant rate of 0.1 mm/s, until the beam failed. During cyclic loading, the beams were loaded at a constant rate of 0.1 mm/sec and unloaded at 0.5 mm/s, according to the loading protocol shown in Fig. 3. Quasi-static cyclic loading history consisted of two phases. The ﬁrst phase was force-control and the second phase was displacement-control. The ﬁrst phase of loading was com- prised of two cycles which imposed a force corresponding to 50 % of the theoretical strength of the test specimen. At the early stage of the second phase of loading, one fully reversed cycle with equal amplitude of 100 % of the yield displace- ment was applied. This phase was followed by several subsequent parts, each containing two fully reversed cycles of equal amplitude, corresponding to 200, 300, 400 and 600 % of the yield displacement.
In the last few decades, many studies have been conducted on the flexural strengthening of reinforced concrete (RC) beams using different strengthening techniques such as concrete, steel and artificial fiber reinforced polymer composites (FRP) -. Among artificial FRPs, mainly glass, carbon and aramid fibers have been considered extensively -. Attari et al., 2012 conducted strengthening of concrete beams using glass FRP sheets, carbon FRP sheets and hybrid FRP sheets. In their study, a total of seven RCbeams were constructed and tested in simply supported manner. All the beams have the same dimensions and the same flexural and shear reinforcements. Two 10-mm diameter steel bars, with a steel ratio of 1.6%, are used for flexural reinforcement at the bottom. Two 8-mm bars are used at the top. Transverse steel consisting of 6-mm diameter stirrups spaced out every 120 mm is used as shear reinforcement. The testing rig is limited to a length of 1500 mm, which imposes to make rectangular beam specimens 160 mm in height and 100 mm in width. The specimen overall
In this paper a series of tests on one-way spanning simply supported RC slabs which have been strengthened in flexure with tension face bonded FRP composites and anchored with different arrangements of FRP anchors are conducted. The load–deflection responses of all slab tests are plotted, in addition to selected strain results. The behaviours of the specimens including the failure modes are also discussed. The test results showed that the increase in strength and deflection recorded, over the unanchored but strengthened control counterparts, was 30% and 110%, respectively. In addition, the usable strain in the FRP plates was increased from 45% of the capacity of unanchored but strengthened control slab to almost 80% of optimally designed anchorage schemes. Anchors positioned in the shear span were found to be most effective. Closer spaced anchors were found to reduce the rate of debonding crack propagation and also enabled higher deflections to be achieved. Anchors spaced far apart led to gains in deflection capacity but limited gains in strength .
A comprehensive three dimensional (3D) finite element (FE) models of RCbeams, flexurally strengthened with CFRP rod panels (CRP’s), were developed. The models consider the nonlinearity of concrete material, including: concrete nonlinear stress-strain behaviour in compression. The structural behaviour of CRP’s, especially the overlap region, was explicitly captured by modelling CFRP rods as discrete reinforcement embedded inside the adhesive layer. The CRP are externally adhered to the bottom of beam surface for strengthening it in flexure. Attachment of CRP onto a structural substrate can be summarized as such: (1) a uniform layer of adhesive is applied onto the substrate. (2) CRP is then brought to its correct position and pressed gently, forcing the adhesive to flow around the rods and fill completely between the rods. Adhesive thickness will approximately be 2-to-3 millimeters greater than rod diameter. Neighbouring panels are brought together and made continuous by overlapping the rods. The overlap length, conservatively selected based on preliminary double- lap shear tests. The CRP adhered to RC beam is shown in figure.2.The configurations are as shown in figure 3 and 4 4.1Analytical modelling
was calculated to be 128 mm. However, as seen in Fig. 6, maximum spacing of 350 mm was used for specimens BS2-O2-CPL, which exceeded the 128 mm calculated from Eq. (6). Therefore, buckling occurred for plates of specimen BS2-O2-CPL. In brief, plate buckling could have been mitigated by the use of either lesser rod spac- ing (not exceeding 128 mm) or plates with larger thick- ness. The validated FE modeling was utilized to study the effect of steel plate parameters on performance of strengthenedRCbeams with web opening located in the zone of high flexure with high shear (case of center-point loading). In this regard, four new strengthening schemes (scheme-3 to scheme-6) were numerically investigated. Details of proposed schemes are shown in Figs. 16 and 17 for beams with 450 and 900 mm opening, respectively. It is clear that scheme-3 is the same as scheme-2 but with reduced rod spacing (maximum spacing of 125 mm was provided as seen in Figs. 16a and 17a). As depicted from Figs. 16b and 17b, strengthening scheme-4 is the same as scheme-2 but with larger plate thickness of 6.0 mm and reduced rod spacing (maximum spacing of 150 mm was (6) smax = πt p
Fiber-Reinforced Polymer (FRP) materials have being widely used in civil engineering applications for more than three decades. Well established analytical models are already available for FRPstrengthenedbeams and columns under flexural and axial loadings. However, the behavior of such members under shear stress field is still under investigation due to the high level of complexity associated with the shear behavior (Zararis 2003). Most of the available analytical models for predicting the shear behavior of FRPRC members resulted in relatively large discrepancies when compared to experimental results (Belarbi et al. 2011). The most important reason for this is the lack of accurate stress strain relationships for FRPRC elements. In the previous developed models and design codes, the shear contributions of concrete, internal steel reinforcements and externally bonded FRP reinforcements were derived independently. However, the high level of interaction between these materials should be considered (Bousselham and Chaallal 2008; Chen et al. 2010). To accurately predict the behavior of FRPRC elements in shear, the stress - strain relationships of each component and the interactions among them have to be carefully investigated.
strengthenedRC plane stress structures Two uniaxial material models for concrete and steel in FRP-strengthenedRC, namely ConcreteF01 and SteelF01 are created and implemented into OpenSees based on the ConcreteZ01 and SteelZ01 material models developed by Zhong (2005). The material model of ConcreteF01 needs five input parameters: the ultimate compressive strength f c , the compressive strain 0 corresponding to f c , FRP reinforcement ratio f , FRP Young’s modulus E f , and the parameter “ c” of concrete in tension,. An object of SteelF01 needs the following parameters: yield stress f y , Young’s modulus E s , concrete compressive strength f c , and effective steel reinforcement ratio se .
Seven full-scale rectangular shearbeams bonded externally using bi-directional discrete CFF strips were tested under three and four point bending systems at the Abstract: This paper presents the experimental and finite element (FE) results of Reinforced Concrete (RC) rectangular beams in shear bonded externally using Carbon Fibre Fabric (CFF) reinforcement. In the experimental study, all, except control, beams were strengthened/repaired with CFF reinforcement at laboratory environment. These beams were tested under four point bending system for failure. Moreover, to validate the obtained experimental results, the study used two-dimensional model to simulate the shear behaviour of the CFF repaired/strengthenedbeams using LUSAS finite element analysis software. The experimental results confirm that the CFF repaired and initially strengthenedbeams attained a gain of 37.28% - 77.95% and 60.71% - 77.34% for shear span to effective depth ratio of 2.5 and 4.0, respectively. The results of FE prediction were compared against the experimental results obtained from the experimental investigation. It was generally found that the comparison between the predicted FE and experimental results show satisfactory correlation in terms of load- displacement profile.
During the tests on side A, several shear cracks developed on side B but crack opening was effectively controlled (maximum width=0.01 mm) by the post-tensioned steel strapping around the latter side. During the tests on side B, the flexural and shear cracks developed during the tests in side A propagated and penetrated deeper towards the loading point as the applied load increased. After the formation of diagonal cracks, the strain recorded in the shear stirrups increased rapidly and, eventually, failure occurred. As expected, all beams with stirrups were dominated by a shear diagonal failure. This was accompanied by stirrup rupture and concrete spalling at the beams’ soffit (Fig. 4b,c). The measured ultimate capacities of the beams with stirrups ranged between 77 and 134 kN.
4. The load carrying capacity of beam SB3, which was strengthened by two layers of U-wrap of length 88 cm in positive moment zone and two layers of U-wrap of length 44 cm over first two layers, was 415 KN which was nearer to the load capacity of beam SB6. The percentage increase of load carrying capacity was 59.61 % , from which it can be concluded that applying FRP in the flexure zone is quite effective method to enhance the load carrying capacity.