International Journal of Civil Engineering and Technology (IJCIET) Volume 10, Issue 01, January 2019, pp. 22-36, Article ID: IJCIET_10_01_003 Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=01 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication Scopus Indexed EXPERIMENTAL STUDY OF CONTINUOUS RC BEAMS STRENGTHENED WITH CFRP FABRICS UNDER TORSION Saad Khalaf Mohaisen* Civil Engineering Department, Al-Mustansiriyah University, Iraq. *corresponding author ABSTRACT In the last ten years or a little more, CFRP strips and fabrics have been successfully externally bonded to rehabilitate the concrete structures. Most of the previous research focused on the use of CFRP as an enhanced material to improve flexural, shear, ductility and ductility behaviour and confinement of concrete structural members, while limited attention was paid to the investigation of strengthened reinforced concrete (RC) members against torsion, particularly continuous concrete beams. This study aims to detect experimentally the CFRP strengthening technique for continuous RC beams exposed to pure torsion. The experimental program includes investigation of two groups of beams; the first group was composed of twelve un-strengthened beam specimens and the second one includes a total of twelve strengthened beam specimens; all were experienced under pure torsion. Factors considered in the testing program included the effects of concrete compressive strength and the angel of a twist. The angle of twist at each level of force applications, torque at first crack, ultimate torque was to be in comparison with for control and strengthened beams. The outcomes of the tests indicated that all beams wrapped with CFRP fabrics resulted in improvement in tensional resistance as compared with the reference specimens. Key words: Torsion; Composite construction; Continuous beams; Concrete; CFRP sheets. Cite this Article: Saad Khalaf Mohaisen, Experimental Study of Continuous RC Beams Strengthened with CFRP Fabrics Under Torsion., International Journal of Civil Engineering and Technology, 10(01), 2019, pp. 22β36 http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=01 1. INTRODUCTION It is well known that the deterioration of concrete structural elements is a major issue and that it threatens the world in general. Many structural elements and bridges undergo large torsional moments that seriously affect design and may therefore require futher reinforcement. As a safe, http://www.iaeme.com/IJCIET/index.asp 22 editor@iaeme.com Saad Khalaf Mohaisen economical and reasonable concept, it is appropriate to make some repairing and strengthening the existing reinforced concrete structures with fiber reinforced polymer (FRP) which is better than other processes, like reinforcing by steel plates. Such a rehabilitation method also proved previously to be useful in gaining and upgrading the capacity of carrying load carrying for the existing members of reinforced concrete (RC). Most of the structures that already existing were designed under older code provisions which inopportunely do not obey the requirements of recent periods. There is therefore a necessity to find a modern way to increase the capacity of these structures in order to satisfy the new requirement. This reinforcement and repair are usually conducted by FRP bonded sheets for reinforced concrete members. These FRP sheets can be made of carbon, glass or other materials with a similar fiber characteristic. Enhancement with these materials provides many advantages due to its excellent properties, a high tensile strength of high hardness ratio, corrosion resistance, excellent fatigue behavior, and durable. In addition to these unique features, FRP fabrics can be easily installed and applied in situ without specialized equipment. There is a lack of research on the promotion of RC members who are subject to sprains with FRP compounds. Unfortunately, design guidelines are rarely available in [1, 2, 3, and 4]. This absence of experimental testing and studies combined with full interest in the use of FRP materials in the retrofit of the concrete structure that failed to sprain was directed through this study of continuous RC beams subject to twisting and reinforcement with CFRP fabrics. Retrofitting of RC elements against torsional moments using FRP was less of a concern than researchers [5, 6, 7]. Reinforcing RC members with FRP increases load capacity in bending, shear, and succession as well as changing failure patterns [8]. In practice, it is rarely able to wrap the cross section of the RC beams completely because of the presence of floorboards or edges. Therefore, most researches conducted on FRP had reinforced RC members studying rectangular sections completely wrapping by FRP [2, 8, 9, and 10] and only a few studies have studied T-beams with U jackets [11]. The research tool pointed out that the deformation of the RC beams strengthened against torsion is similar to that which has not been strengthened; however, the external bonding inhibits the formation of cracks, reproduction, and expansion to limit the gap between the cracks [10, 11]. The few studies related to the enhancement of FRP sprain have shown that continuous rounding is more effective than tape use [12, 13, 14 and 15]. A spiral wrap at an angle of 45 ° is more effective than a vertical wrap [13, 16]. The final resistance strength of the package is supported by full-length fabrics higher than the strength of the three-sided beam, also called U-wrap [14, 16]. In addition, the use of anchors greatly increases the torsional capacity of RC members [16]. However, FRP bonded externally limited the spread of cracks and widened the gap between the cracks, as well as increased concrete involvement to resist sprains [15-19]. The structural members under torsional forces may be cracked if they are not steel reinforcement distributed correctly. Furthermore, the changes in loading values, loading distribution or deterioration of the overall structural members cause defects in resistance to torsion. Also, in the last earthquake, it was seen that incorrect designed structural members were failed or severely damaged and even collapse in some cases. Such behavior that may cause disasters that indicate the need for retrofitting of poor structures due to seismic effects. Reinforcement of structural elements allowed to give resistance for the strength increases demands which predicted by the structural analysis, without recognizable changing in the overall behavior of the structure under loadings. Fiber reinforced polymers composites can effectively be used as an additional external reinforcement for increasing loads carrying capacity of deficient reinforced concrete structures [20]. Ghobarah, et.al. [14] studied the efficiency of FRP supporting for both of columns and beams exposed to torsional forces. They http://www.iaeme.com/IJCIET/index.asp 23 editor@iaeme.com Experimental Study of Continuous RC Beams Strengthened with CFRP Fabrics Under Torsion have tested 11 beams wrapped with a different angle of orientations of carbon fiber reinforcements polymers (CFRP) and glass fiber reinforcement polymers (GFRP). Fully wrapping the zone of torsion forces of RC beams was found to have considerable positive effects. FRP fibers oriented by 45° showed the further efficacy of the material. Santhakumar, et.al. [20] Prepared a numerical research on unstrengthened and strengthened concrete beams under both effects of torsion and bending and by the finite element method (FEM). They stated the enhancement in the behavior by applying of CFRP laminates being very efficient only after the first cracking of the RC beams, but there is no considerable influence on the unstrengthened stiffness of the beam. The laminates oriented with an angle ±45 degree were more efficient for higher twisting magnitudes to bending moment proportion. Performance and strengthened concrete element behavior that strengthened with externa GFRP sheets bond exposed to pure torsion were studied by Panchacharam and Belarbi [15]. Eight beams were tested and investigated in the study, and various GFRP orientations were used. The involvement of FRP sheets in both of the longitudinal direction of the beam and accompanied with fully wrapped laminates displayed an enhancement in both the ultimate load carrying capacity and ductility of the strengthened beam. An experimental and numerical study was carried by Ameli, et.al. [18] on a twelve rectangular RC beams reinforced by CFRP fabrics / GFRP fabrics fully wrapping with various orientations and configurations. The strengthened beam with FRP was modeled numerically by ANSYS software. Considerable enhancement in the ductility of RC beams was spotted wrapping with GFRP fabrics as comparison with CFRP fabrics. An analytical technique for assessing the torsional capacity for carrying FRP supported RC beams was mentioned by Ameli and Ronagh [21] by taking the concrete interaction with steel and FRP composite. The technique developed by them was in close agreement with experimental results of fully wrapped RC rectangular beams. Chalioris [16] assessed the effectiveness applying epoxybonded CFRP fabrics as an external transverse supporting reinforcement to an under-reinforced beam with rectangular cross-section have flanges exposed to pure torsional forces. A total of 14 RC rectangular cross-sections and T-section experimental models with 1.6m span length were tested under external torsion forces only. A considerable number of studies were conducted on the shear and bending strengthening of RC rectangular beams with outwardly bonded reinforcement (EBR) using CFRP composites. However, in reference to shear and bending, still there are several enquiries concerning the difficulty and the nature of mechanism failure for RC beams supported in torsion by CFRP fabrics, especially for continuous RC beams. Accordingly, the current study aims to discover the development in the resistance of continuous RC beams against torsion force with various angles of a twist, experimentally. The behavior and performance of RC members that supported with EBR CFRP sheets exposed to torsion is existing in the current paper. A total of 16 datasets of continuous concrete beams (8 as references and 8 CFRPstrengthened beams) were calmed from this study to discover the performance of RC continuous beams under pure torsion. Developing the resistance of RC beams against torsion force by using EBR CFRP fabrics was illustrated to be effective. The results indicated that an enhancement in the torsional capacity carrying CFRP-strengthened beams comparison with the reference beams. 2. THE SIGNIFICANCE OF THE PRESENT INVESTIGATION Research into the use of EBR CFRP composites is very advanced developed in flexural, and shear reinforce as an external bonded reinforcement. On the other hand, a literature survey http://www.iaeme.com/IJCIET/index.asp 24 editor@iaeme.com Saad Khalaf Mohaisen carried out by the author who observed that there are a limited experiments and researches on torsional concrete beams reinforced with CFRP sheets, especially for continuous concrete beams. Thus, this study tries to bridge this mentioned gap in the literature by studying the performance of continuous concrete beams reinforced by CFRP sheets under pure torsion. 3. LIMITATIONS The present study has been conducted on rectangular beams. Only four groups of beamspecimens have been studied. These groups differ from each other regarding the concrete compressive strength and the eccentricities. The longitudinal and shear reinforcements are kept constant for all types of beams. Similarly, the results are limited to the pure torque applied and no effect of shear force and bending moment has been considered. 4. AN EXPERIMENTAL PROGRAM 4.1. RC beams details and material characteristics Sixteen concrete test beam samples (sorted into four groups) were cast and evaluated in the present study. Eight of them were strengthened with CFRP sheets. Each of those samples has a clear span of 2000 mm and has a rectangular cross sectional with (width and depth) which (100 and 200)mm respectively. Four deformed steel bars of D10 mm were using as longitudinal reinforcement, while for the web reinforcement D8 mm deformed steel bars spaced 100 mm were utilized. Beams cross-sectional dimensions, rebar layouts, and the preparation of the CFRP fabrics are shown in Figure 1. The sample beam designation system is shown in Figure 2 which considers codes for concrete compressive strengths and eccentricities. For the case of longitudinal reinforcements, a ratio of 0.08 was used for all specimens. The layout of reinforcement was designed to be a little bit under the lowest torsional carrying required capacity in present design standards. This was to simulate RC beams that were deficient under torsional forces. Uniform level (20 mm) of the cover of concrete that used for all specimens. The specimens were casting by a ready concrete mix. The compressive strength of concrete mix was 30 MPa and 60 MPa, when using 2 cm of coarse aggregate as a maximum size for all specimens. The concrete compressive strength is done with the aid of concrete cylinders (height of the cylinder 300mm and its diameter is 150 mm). Cylinders of concrete were casting with the same specimens batch of concrete mixture, and all of them were undergone to the ame curing conditions. Standard CFRP coupon tensile tests were applied to find the mechanical features of the steel reinforcing. The longitudinal shear reinforcements and yield strengths were tested and they were 430 and 484 MPa respectively. Details of concrete mixes are given in Table 1 showing their properties. Table 1 Features of concrete mixture. The CFRP fabrics used in this experimental work were supplied from the Chemical Company (BASF) by commercial name "MBrace CF 130". The sheet of CFRP has a one-way arrangement of fibers, with a thickness of 0.166 mm/ply for every layer. The weight of the http://www.iaeme.com/IJCIET/index.asp 25 editor@iaeme.com Experimental Study of Continuous RC Beams Strengthened with CFRP Fabrics Under Torsion CFRP is also 300 g / m2. The adhesive, was brought from the same company which commercial called "MBrace saturant 2525" to use it as a binding agent. This adhesive material contains a two essential components which is resin and fermenting material. And the mixing proportion of 3: 1 and must be used within 30 minutes after starting the mixing. The manufacturing company gave the physical characteristics of the materials that provided, which are summarized in Table 2. The adhesive is expected to be always environmentally friendly to have a durable and resistance against environment. This will allow and enhance the strengthening of the reinforced member of concrete to ensure the life expectancy of the structure is guaranteed. The strengthening by CFRP was performed in the third week after the process of casting the beam. Depending on the surrounding temperature, the process of curing was performed for minimum two days because it is required to strengthen the CFRP for each technical datasheet. A 0.75D of CFRP strip spacing was used, D is all depth of the beam. Also 10 cm overlapping length was used in the direction of the longitudinal fibers. Figure 1 RC beams depth dimensions, the reinforcement layout and scheme CFRP that used in the study Figure 2 The system of designation of the sample Table 2 typical properties of CFRP sheets and epoxy http://www.iaeme.com/IJCIET/index.asp 26 editor@iaeme.com Saad Khalaf Mohaisen 4.2. Test procedure and instrument Torque was applied at different eccentricities within the zone of test via the arm lever of a 3000kN hydraulic capacity for a world-wide machine for testing (MFL system) actuator as illustrated in Figure 3. Where the cells of loading were put under a rounded seat and the actuator of hydraulic to gauge the applying torque. Linear variable displacement transducers (LVDTs) were applied for determining the exact amount of deflection and hence the angle of twist. Placing of a singular supporting status which allowed to rotate on longitudinal axis, and arms of lever are fixed to the sample to provide a torsion moment as indicated in Figure 4. When the lever arm position corresponding with the support arm, the sample undergoes to a twisting alone. So as to applying various torsion moment, a lever arm length and position could be adjusted. The using of three dial gauges, where two of those three were used to measure the displacements below the arm of lever, and the final one was put at the beam centre for measuring the displacement at this position. Distances of (30, 40, 50, and 60) cm were kept between the face of supporting and lever arm for producing torsion. Figure 5 display the schematic diagram of the test setup. The load is transferred from the hydraulic arm to the sample via a package distributed at the end of the crane attached to the sample. Therefore, half the load which applied will work at each lever arm end. When the load located at the lever arm ends is away from the longitudinal axis of the beam and away from supporting of the sample, it will result in torsion. 100 mm 60 cm 50 cm 40 cm 30 cm Figure 3 Different distances of the applied load. Two members of steel produced from structural steel clips were fixed around the two ends of the concrete beams to work as arms of lever for applying the torsion moment. These arms of lever are fixed around the beam as demonstrated in Figure 5. A long steel I-beam with wide flange was laid down diagonally to rest on hinged at the supported end on top of the arms of lever. Where I-beam had been loaded at the centre of this beam. The benefit of setting up this test is to apply a singular vertical load, thus the mid-section of the RC beam between loads is undergone to torsion force alone. So as to avoiding the crushing concrete locally near to supporting points, where the pads of neoprene are put between the steel plate and the beams sides for the arms of twisting.. The medium of twist angle per unit of beam length was estimated by two measurements of LVDTs at high resolution. These two LVDTs, measure the corresponding deformation of each sample during rotation. http://www.iaeme.com/IJCIET/index.asp 27 editor@iaeme.com Experimental Study of Continuous RC Beams Strengthened with CFRP Fabrics Under Torsion Figure 4 Photo of the setting up of the test Figure 5 Graphical outline for the setting up of torsion test Figure 6 demonstrates the internal forces in the beam model when exposed to the torsion by means of opposite external loads. Torque is produced in the central part of the sample by a load at the end of the arm of lever (half the load applied) multiplying by the length of the arm of lever from the centre of the sample. The twist angle was found in each arm of lever of the vertical displacement and lever arm length. The overall angle of twit in the middle part (central) is the total twist angle in the two arms of lever the arm. http://www.iaeme.com/IJCIET/index.asp 28 editor@iaeme.com Saad Khalaf Mohaisen Figure 6 The diagram of internal force for the sample subject to pure torsion. 5. DISCUSSION OF RESULTS In this research the pure torsion was applied on sixteen beams samples to test them and study the impact of various parameters which take into the consideration. Eight samples were unstrengthened concrete beams. In this section, the results of the tests will be discussed depending on the behaviour of torqueβtwist, the CFRP impact on ultimate torque, modes of failure and cracking. The ultimate load, load of cracking and the angle of twisting at ultimate load for all beams which had been tested as listed in Table 3. Table 3 Cracking and ultimate load also twist angle for the current experimental program at ultimate load. Group No. 1 2 3 4 f'c Mpa Eccentricity (cm) Cracking Load (kN) Ultimate Load (kN) π΅π β πΜπ 30 β π1 π΅π β πΜπ 30 β π2 30 30 55 72.5 Twist Angle at Ultimate Load (degree) 8.18 30 40 40 56.5 9.63 π΅π β πΜπ 30 β π3 π΅π β πΜπ 30 β π4 30 50 30 47.5 10.82 30 60 20 36.5 11.98 π΅π β πΜπ 60 β π1 π΅π β πΜπ 60 β π2 60 30 85 107.5 6.17 60 40 70 90 7.33 π΅π β πΜπ 60 β π3 π΅π β πΜπ 60 β π4 60 50 55 74 8.59 60 60 45 67.5 9.59 π΅πΉ β πΜπ 30 β π1 π΅πΉ β πΜπ 30 β π2 30 30 60 78 6.92 30 40 45 63 8.56 π΅πΉ β πΜπ 30 β π3 π΅πΉ β πΜπ 30 β π4 30 50 35 52 8.6 30 60 20 41 9.84 π΅πΉ β πΜπ 60 β π1 π΅πΉ β πΜπ 60 β π2 60 30 110 125 1.19 60 40 110 123 1.34 π΅πΉ β πΜπ 60 β π3 π΅πΉ β πΜπ 60 β π4 60 50 90 100 1.22 60 60 65 80 0.96 Beam ID http://www.iaeme.com/IJCIET/index.asp 29 editor@iaeme.com Experimental Study of Continuous RC Beams Strengthened with CFRP Fabrics Under Torsion 5.1. Crack Behaviour and Modes of Failure The modes of failure for unstrengthening and CFRP-strengthened reinforced concrete beam specimens exposed to torsion are presented in Figure7. However, the appearing of the first vertical cracks of the unstrengthening beams was at mid of the vertical forces. Where the initiation of the tension cracks which diagonally inclined and propagated in spiral patterns shape. Then the cracks are gradually enlarged with increasing of the load for the segments of the two beams that rotating relatively one to another one on the RC beams centroid axis. In some strengthened beam specimens, debonding failure of CFRP sheets is noticed at different places, as seen in Figure 7. Initially, vertical cracks were noticed at the bottom of specimen side faces. The cracks of torsion that take a diagonal shape were taken placed and expanded in the concrete parts that unwrapped and between the strips of the four sides of the tested beams. The failure is partially delayed comparison with unstrengthening samples. Failure of CFRP fabric started by tearing off the bottom corner longitudinal strip as demonstrated in Figure 7. Figure 7. The failure shape of the tested samples under torsion. 5.2. A comparison of Cracking and Ultimate Torque Figure 8 demonstrated a comparison with moment at the ultimate torque and first crack for unstrengthened beam specimens and beams strengthened with CFRP strips tested in torsion. For 30 MPa tested beams with eccentricity (30, 40, 50, and 60) cm exhibited maxima of (10.9, 17.5, 20, and 20) % increase in cracking torque and maxima of (7.6, 11.5, 9.5, 12.3) % increasing in ultimate torque amongst all the tested strengthened beams. Moreover, compared to unstrengthened beam specimens, there were increases in cracking and ultimate torque of (29.4, 57.1, 63.6, and 44.4) % and (16.3, 36.7, 35.1, and 18.5) %, for 60 MPa concrete compressive strength. To conclude, the torsional RC beams wrapped with CFRP sheets displayed a great increasing in the crack, ultimate deformations of twist and ultimate strength for all wrapped beams by CFRP sheet. It could be concluded by that wrapped beams have generally an improving in the capacity of the torsional moment significantly by up to 64%. http://www.iaeme.com/IJCIET/index.asp 30 editor@iaeme.com Saad Khalaf Mohaisen 30 MPa Torque, kN.m 35 30 25 20 15 10 5 Beam ID Cracking torque Utimate torque 60 MPa 65 Torque, kN.m 55 45 35 25 15 5 Beam ID Cracking torque Utimate torque Figure 8 The comparison the tested beams between the ultimate torque and cracking torque 5.3. Torque-Twist Comparison 5.3.1. Unstrengthened concrete beams Eight unstrengthened continuous beam specimens with different load eccentricities (300, 400, 500, and 600) mm were tested and evaluated. Torque-Twist curves of unstrengthened beams that tested under a torsional force are presented in Figure. 9for all of the investigated different concrete compressive strengths values. All the tested beams showed the same behaviour for twist angle and torque. Specimens π΅π β πΜπ 30 β π1andπ΅π β πΜπ 60 β π1displayed better ductility comparison with other specimens. Least angle of twist was recognized in the case of http://www.iaeme.com/IJCIET/index.asp 31 editor@iaeme.com Experimental Study of Continuous RC Beams Strengthened with CFRP Fabrics Under Torsion the unstrengthened specimen. For different concrete compressive strengths, the results showed considerable increment in torque of specimens for all the eccentricities. The ultimate torque capacity increased by approximately (86.9%and133%) for 30 and 60 MPa, as shown in Figure 9. Moreover, the angle of twist increased (46% and 55.6%) for the different concrete compressive strengths. 80 Torque, kN.m 70 60 BR-fc30-e1 50 BR-fc30-e2 40 BR-fc30-e3 30 BR-fc30-e4 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Angle of twist, deg/m (a) 30 MPa 140 Torque, kN.m 120 100 BR-fc60-e1 80 BR-fc60-e2 60 BR-fc60-e3 40 BR-fc60-e4 20 0 0 1 2 3 4 5 6 7 8 9 10 11 Angle of twist, deg/m (b) 60 MPa Figure 9 Torsional behavior of unstrengthened beam specimens under different eccentricities for (a) 30 MPa and (b) 60 MPa. 5.3.2. CFRP-strengthened concrete beams As described in the last subsection, eight CRP-strengthened beam specimens with different load eccentricities (300, 400, 500, and 600) mm were tested and evaluated. Two grade of concrete namely (30MPaand 60MPa), were used in this experimental program. The torque and twist behavior of CRP-strengthened beams subject to torsion force is shown in Figure. 10, for different concrete compressive strengths. All the tested beams showed similar behavior for torque and twist angle. Specimens π΅πΉ β πΜπ 30 β π1and π΅πΉ β πΜπ 60 β π1 displayed better ductility compared to other specimens. For different concrete compressive strengths, the results displayed a considerable increase in torque capacity of specimens corresponding to all http://www.iaeme.com/IJCIET/index.asp 32 editor@iaeme.com Saad Khalaf Mohaisen eccentricities. The ultimate torque capacity increased by approximately 7.3% and26.5% for 30 and 60 MPa, respectively. This was shown in Figure 10. Moreover, the angle of twist increased by42.2% and 246%for the different concrete compressive strength. BR-fc30-e3 BR-fc60-e3 Torque, kN.m 120 100 80 60 40 20 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Angle of twist, deg/m BR-fc30-e4 BR-fc60-e4 140 Torque, kN.m 120 100 80 60 40 20 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Angle of twist, deg/m Figure 10 Torsional behaviour of CFRP-strengthened beam specimens under different compressive strength. 5.3.3. Comparison between unstrengthened and CFRP-strengthened concrete beams All samples wrapped with CFRP showed higher torque resistance comparison with the unstrengthened beam specimens. As described in Figure 11a, the results showed that the http://www.iaeme.com/IJCIET/index.asp 33 editor@iaeme.com Experimental Study of Continuous RC Beams Strengthened with CFRP Fabrics Under Torsion cracking torque capacity increased by approximately (11% - 20%) for 30 and (29.4% - 64%) for 60 MPa. Moreover, the ultimate torque capacity increased by (7% -11%) and (14% -27%) for (30MPa and 60MPa) concrete compressive strength. CFRP Contribution, % 70 60 50 40 30 20 10 0 30 40 50 60 Eccentricity, cm 30 Mpa 60 Mpa (a) CFRP Contribution, % 30 25 20 15 10 5 0 30 40 50 60 Eccentricity, cm 30 Mpa 60 Mpa (b) Figure 11 CFRP contribution for (a) cracking torque and (b) ultimate torque. 6. CONCLUSIONS An experimental program comprised of sixteen reinforced concrete beams was carried out to find the behaviour of torsional of reference and continuous concrete beams strengthened by CFRP against to different eccentricity values. Depending on the experimental results which had been obtained, so the following conclusions are investigated: ο· The improvement by epoxy that bonded by strips of CFRP is a practical technique for strengthening of continuous concrete beams subject to torsion force. The beam that strengthening by CFRP strips as an external transverse reinforcement showed http://www.iaeme.com/IJCIET/index.asp 34 editor@iaeme.com Saad Khalaf Mohaisen ο· ο· ο· overall a better performance for torsional comparison with unstrengthen beams by up to 64%, as indicated in BR-fc60-e3. The results which had been obtained indicated an increasing in the ultimate capacity of torque by approximately 7.3% and26.5%for 30 and 60 MPa, respectively. Moreover, an increase in the angle of twist of 42.2% and 246% was observed corresponding to the different concrete compressive strength. The beams that wrapped by CFRP strips had been delayed the failure partially comparison with the failure of the reference samples which is due to the existence of CFRP which prevent the initial cracking. However, eventually the diagonal torsional cracks appeared and widened in the beams of concrete that unwrapped while fiber deboning has been noticed for some specimens. All the tested beams had the same torque behaviour and twist angle. Specimens (π΅π β πΜπ 30 β π1 πππ π΅π β πΜπ 60 β π1) for unstrengthening and (π΅πΉ β πΜπ 30 β π1andπ΅πΉ β πΜπ 60 β π1) for beams strengthened with CFRP strips displayed better ductility compared to other specimens. 7. AREA OF FUTURE STUDIES For this work the following recommendations had been summarized to help in the future works: ο· The person needs to realise the results limitations which related to each parameter like (1) CFRP layers number, (2) geometry and type of the device of anchoring, (3) complexity and scale of the samples of spandrel-beam. As well as more researches are required to identify the effect of these parameters. ο· The current research was answered the questions and problems of the behavior of pure torsion for the concrete continuous beams that strengthened by strips of CFRP. However, there are other issues for detailing which need an addressing that relating to the rate of the longitudinal reinforcement, and the influence of the combination of loading (bending, torsion and shear). ο· The improvement of the analytical model of rigorous for analysing the RC beam that strengthened by different CFRP failure modes. REFERENCES [1] [2] [3] [4] P.R. Salom, J. Gergely, D.T. 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