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Journal ArticleDOI

Investigation on Flexural Performance of RC Beams Flexurally Strengthened by Side-bonded CFRP Laminates

09 Mar 2012-The Open Civil Engineering Journal-Vol. 6, Iss: 1, pp 26-32

AbstractIt is an effective way to improve the flexural behavior of reinforced concrete (RC) members by externally bonded carbon fiber reinforcement polymer (CFRP) laminates on the soffit of the members. However, there is little investigation on flexural performance of RC beam flexurally strengthened by side-bonded FRP laminates. To investigate the flexural behavior of RC beams side-bonded CFRP laminates and the difference of RC beams strengthened by soffit-bonded and side-bonded CFRP laminates, a total of 8 CFRP-strengthened beams and 1 control beam were tested. The experimental results show that: 1) the first crack loads of RC beams strengthened by side-bonded CFRP laminates are much higher than that of RC beams strengthened by soffit-bonded CFRP laminates. The first crack loads of side-bonded CFRP laminates beams improved significantly; 2) Side-bonded and soffit-bonded CFRP laminates have almost the same effect on the flexural stiffness of RC beams strengthened with same quantity of CFRP laminates before tension rebar yielding. However, side-bonded CFRP laminates can affect crack width and crack pattern of the strengthened beams, and the pre-crack stage of RC beam by side- bonded CFRP laminates extended remarkably. 3) different to soffit-bonded CFRP laminates RC beams, side-bonded CFRP laminates cannot improve the first yielding and the ultimate load bearing capacity of RC beams.

Topics: Beam (structure) (51%), Flexural strength (50%)

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Citations
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Journal ArticleDOI
Abstract: The conventional method of strengthening reinforced concrete (RC) beams in flexure is via bonding carbon-fiber reinforcement polymer (CFRP) laminates to the beam’s soffit. However, the beam’s soffit could be narrow or inaccessible for strengthening. To overcome such obstacles, this paper explores the feasibility of strengthening RC beams in flexure by side-bonded CFRP composite sheets. Accordingly, a total of nine RC beams have been cast, eight of which were strengthened in flexure with different configurations of bottom-bonded and side-bonded CFRP sheets, and tested under four-point bending till failure. The load-deflection response curves, failure modes, and ductility of the tested specimens were recorded and compared. Overall, it is observed that specimens strengthened with similar amount of reinforcement are comparable with percent increase in the flexural strength over the control beam ranged from 62 to 92% for bottom-bonded and 39.7–93.4% for side-bonded strengthened beams. In addition, an analytical model based on ACI 440.2R-08 guidelines is developed and the predicted flexural strength was in good agreement with experimental results with differences ranging between 2.4% and 6.8%. It is concluded that the proposed side-bonded strengthening scheme is a valid alternative to the bottom-bonded scheme of strengthening of RC beams in flexure.

46 citations


Journal ArticleDOI
Abstract: Reinforced concrete (RC) beams are often strengthened through externally bonded (EB) fiber-reinforced polymer (FRP) systems. In such applications, improving the bending capacity of RC beams is of main interest and which is achieved via bonding EB-FRP systems to the soffit of beams. Access to soffit of beams can be restricted by existing structural members or limited (in case a RC beam span over neighboring compartments). In those scenarios, RC beams can still potentially be strengthened in flexure through longitudinal bonding of EB-FRP systems to the sides of beam's web. This paper examines critical parameters that influence the effectiveness of side bonded EB-FRP systems through a newly developed finite element (FE) model. This model utilizes state-of-art simulation techniques and is capable to trace the flexural behavior of RC beams externally strengthened with side-boned FRP laminates throughout all loading stages till failure. The model was validated by comparing with experimental data and the predicted and measured results were in good agreement. The validated model was then utilized to study the effect of concrete compressive strength, FRP material type, FRP size, and steel reinforcement ratio on the behavior of strengthened RC beams. Outcomes of this numerical investigation show the effectiveness of side-bonding FRP systems as an alternative to conventional soffit strengthening systems to improve the flexural capacity of RC beams.

33 citations


Cites background from "Investigation on Flexural Performan..."

  • ...[26] compared the performance of a number of RC cantilever beams strengthened with carbon based FRP (CFRP) laminates....

    [...]

  • ...4 In order to overcome some of these challenges, bonding of FRP strengthening systems to the sides of beam’s web in the longitudinal direction to enhance flexural capacity of RC beams has been identified as a possible solution [25-28]....

    [...]

  • ...[26], the RC beams strengthened with CFRP bars experienced less cracking than that with steel bars....

    [...]

  • ...[26] also reported that SB-FRP systems led to a lower crack width and reduced crack pattern in FRP-strengthened beams, which translated to a significant increase in the pre-crack stage of FRP-strengthened RC beams....

    [...]

  • ...While this procedure is proven effective in most loading scenarios, it may not be suitable or applicable in certain situations such as those associated with unique architectural arrangements, especially in beams with narrow/tapered geometric configurations such as double-tees, or in beams with limited working space/accessibility (attached to partition walls or spanning to multiple compartments) [25-27]....

    [...]


01 Jan 2000
Abstract: Very advanced design rules have already been developed at the University of Adelaide for adhesive bonding steel plates to reinforced concrete beams in order to prevent premature debonding by shear peeling or flexural peeling. The aim of the present study was to determine experimentally whether these design rules, which were developed for steel plated beams, could be applied to fibre reinforced plastic (FRP) plated beams. This paper compares, with the help of test results, the shear and flexural debonding mechanisms of steel and FRP plated beams.

30 citations


Journal ArticleDOI
Abstract: An experimental study is presented on the behaviour of reinforced concrete (RC) beams retrofitted externally with glass fibre reinforced polymer (GFRP) fabrics. Out of ten beams, one beam without GFRP and nine beams wrapped in various lay-up patterns with one, two, three and four layers of GFRP fabrics have been tested for flexure under two-point loading. Loads corresponding to the first crack/delamination and ultimate failure of the beams have been recorded and types of failure have also been observed. Load versus deflection graphs have been plotted at salient locations of beams. Thereafter, a critical discussion has been made with respect to increase in the flexural strength of retrofitted beams as compared to the control beam in order to explore the optimal use of GFRP fabrics for strengthening the RC beams. In addition, a design proposal has been developed in extension to IS: 456-2000 to predict the ultimate design strength of RC beams strengthened with fibre reinforced polymer (FRP) fabric sheets. Thereafter, the values of the experimental flexural strength of the strengthened RC beam have been compared with the corresponding values of design flexural strength computed from present formulation and ACI: 440-2R-08 for its validation. The results obtained from the present experimental study show that flexural strength of the strengthened RC beams increases with increase in number of layers for all lay-up patterns. However, the beams wrapped with two layers GFRP fabrics in the tension face and half of the both sides below neutral axis show superior performance with respect to flexural strength, ductility and economy.

25 citations


Journal ArticleDOI
Abstract: The strengthening reinforcement is glued to the soffit of the reinforced concrete (RC) beams in the mainstream externally bonded reinforcement (EBR) technique for flexural strengthening. However, the soffit of RC beams could be inaccessible for strengthening due to limited or no space at the soffit because of walls or doors, or the spalling of concrete. To overcome such difficulties, this paper investigates the feasibility of the flexural strengthening of lightweight non-pre-cracked and pre-cracked reinforced concrete (RC) beams using the side externally bonded reinforcement (S-EBR) technique with carbon fiber reinforced polymer (CFRP) fabric. A total of eight full-sized RC specimens were fabricated, strengthened, and tested under four-point loading until failure. The test variables were the internal reinforcement ratio, percentage of pre-cracking loads, and the effect of cracking loads on the flexural performance. The loads, deflection, and ultimate failure of the specimens were recorded and the types of modes of failure were also observed. The S-EBR strengthening technique with CFRP fabric significantly enhanced the flexural capacity of non-pre-cracked and pre-cracked lightweight RC beams compared to the control specimen. An analytical model in accordance with ACI 440.2R-08 was developed to verify the experimental results. The flexural capacity predicted by the model was in reasonable agreement with the experimental results.

6 citations


References
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Journal ArticleDOI
Abstract: Retrofitting by plating structures has been found to be very efficient. However, tests have shown that externally bonded longitudinal plates are prone to premature debonding. Furthermore, a comprehensive study of published research has also shown that there can be large discrepancies between debonding mathematical models and tests. To overcome this problem and to allow structural engineers to adhesively bond plates with safety and efficiently, a structural engineering approach is suggested whereby many of the debonding mechanisms can be prevented by judicious detailing; this approach can be applied to tension face plates, compression face plates, side plates, U-sectioned plates, and angle-sectioned plates. Four continuous reinforced concrete beams have been retrofitted with adhesively bonded longitudinal plates and tested in order to illustrate this design approach, to directly compare the performance of longitudinal side plates with longitudinal tension face plates, to compare FRP plating with steel plating, and in particular to illustrate the effect of debonding on the sectional ductility of longitudinally plated continuous RC beams.

63 citations


"Investigation on Flexural Performan..." refers background in this paper

  • ...To investigate the flexural behavior of RC beams side-bonded CFRP laminates and the difference of RC beams strengthened by soffit-bonded and side-bonded CFRP laminates, a total of 8 CFRP-strengthened beams and 1 control beam were tested....

    [...]


Journal ArticleDOI
Abstract: Eighteen reinforced concrete beams, including 16 beams strengthened with CFRP laminate at different levels of preload and 2 control beams, were tested to investigate the influence of preload level on flexural behavior of CFRP-strengthened RC beam. The experimental parameters include rebar ratios, number of plies of CFRP laminates and preload level at the time of strengthening. Theoretical analysis was also carried out to explain the experimental phenomena and results. The experimental and theoretical results indicated that the preload level has more influence on the stiffness and deflection of the strengthened beam, both at post-cracking and post-yielding stage, than that on the yielding and ultimate flexural strength of the strengthened beam. The main failure mode of CFRP-strengthened beam is the intermediate crack-induced debonding of CFRP laminates, provided that the development length of CFRP laminates and shear capacity of the beam are sufficient.

43 citations


01 Jan 2000
Abstract: Very advanced design rules have already been developed at the University of Adelaide for adhesive bonding steel plates to reinforced concrete beams in order to prevent premature debonding by shear peeling or flexural peeling. The aim of the present study was to determine experimentally whether these design rules, which were developed for steel plated beams, could be applied to fibre reinforced plastic (FRP) plated beams. This paper compares, with the help of test results, the shear and flexural debonding mechanisms of steel and FRP plated beams.

30 citations


Journal ArticleDOI
Abstract: Very advanced design rules have already been developed for adhesive bonding steel plates to reinforced concrete beams in order to prevent premature debonding by either shear peeling or flexural peeling. The aim of this study is to determine experimentally whether these design rules that were developed for steel plated beams and slabs, can be applied to fiber reinforced plastic (FRP) plated beams. This paper compares, with the help of test results, the shear and flexural debonding mechanisms of steel and FRP plated beams.

27 citations


"Investigation on Flexural Performan..." refers background in this paper

  • ...To investigate the flexural behavior of RC beams side-bonded CFRP laminates and the difference of RC beams strengthened by soffit-bonded and side-bonded CFRP laminates, a total of 8 CFRP-strengthened beams and 1 control beam were tested....

    [...]


01 Jan 2005
Abstract: To investigate the effects of externally bonded carbon fiber reinforced polymer(CFRP) sheets on the flexural performance of the beams strengthened at different levels of sustaining load, test of 16 RC beams retrofitted with CFRP sheets and 2 control beams was carried out The bearing capacity and stiffness of the beams were analyzed in detail The parameters of the test include the reinforcement ratio, quantities of CFRP sheets, and sustaining load level at the time of strengthening The experimental and analytical results led to the conclusions summarized as follows: 1) the stiffness of cracked beams retrofitted with CFRP sheets is greater than that of the control beams 2) the yielding load and ultimate bearing capacity of the beams are not affected by the value of the sustaining load at that load RC beams retrofitted with CFRP sheets, but affect the stiffness of the beams, especially the average tangent stiffness after rebar yielding The experimental and analytical results are valuable for authorizing codes and for practical engineering

1 citations