CFRP Mechanical Anchorage for Externally Strengthened RC Beams under Flexure (original) (raw)
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De-bonding of carbon fiber reinforced polymers (CFRP) sheets and plates from the concrete substrate is one of the major reasons behind premature failures of beams that are externally strengthened with such CFRP materials. To delay or prevent de-bonding and therefore enhancing the load carrying capacity of strengthened beams, several anchorage systems were developed and used. This paper investigates the use of CFRP mechanical anchorage of CFRP sheets and plates used to externally strengthen reinforced concrete beams under flexure. The pin-and-fan shape CFRP anchor, which is custom-made from typical rolled fiber sheets and bundles of loose fiber is used. Several reinforced concrete beams were casted and tested in standard four-point bending scheme to study the effectiveness of this anchorage system. The beams were externally strengthened in flexure with bonded CFRP sheets and plates and then fastened to the soffit of the beams' using various patterns of CFRP anchors. It is observed that the CFRP plates begins to separate from the beams as soon as de-bonding occurs in specimens without CFRP anchors, while in beams with CFRP anchors de-bonding was delayed leading to increase in the load carrying capacity over the un-anchored strengthened beams.
Engineering Structures, 2020
This paper investigates the behavior of reinforced concrete beams strengthened in flexure using externally bonded carbon fiber reinforced polymer (CFRP) rod panels (CRPs) fabricated using 4 mm rods spaced at 9.5 mm. The experimental program consisted of a control beam and three beams strengthened with either a continuous CRP, a spliced CRP with two half-length CRPs spliced through a 150 mm finger joint, or a spliced and end-anchored CRP. Spliced panel performed similar to the continuous one, with no debonding observed at finger joint. They resulted in a comparable strength increase relative to the non-strengthened control beam of 95 and 104%, respectively, and failed by concrete cover separation (CCS) at CRP end. When the spliced CRP was end-anchored, the increase in strength was 195% relative to the control beam, with the finger-joint still intact, and the failure mode changed to intermediate crack-induced debonding (ICID). The analytical model, developed from sectional analysis and strength models for debonding failures, is capable of predicting the load-deflection response and ultimate loads, including the two observed debonding failures. For CCS failure, two models are presented, one is based on the concrete tooth model, and the other on the shear capacity model. The ICID failure was based on limiting the CFRP strain in accordance with ACI 440.2R-17 design guide. Results showed a good correlation between analytical predictions and test data.
Fibers, 2015
This research program is intended to verify the influence of using distributed external U-wrap CFRP anchorage to shift the failure mode from overall debonding to sectional flexural failure for concrete beams externally bonded with CFRP sheets. Premature cover delamination and FRP debonding are predominant failure modes in FRP flexural strengthening that may be delayed or prevented by using FRP anchorage. The present experimental study aims to comparatively prove that proper anchorage of flexural strengthening is anticipated to yield a classical flexural failure by FRP rupture or concrete crushing. Once the cohesion of concrete and/or the adhesion with the FRP is exhausted, the U-wraps are engaged to provide anchorage to the flexural FRP through shear friction. Accordingly, three identical T beams and three identical rectangular beams were designed and constructed to examine the capacity improvement by preventing premature debonding failure. The first specimen in each series was tested as a control beam. The second specimen in each series was strengthened using five layers of flexural CFRP in order to admit a debonding failure. The third specimen in each series was strengthened with the same five layers of flexural CFRP plus additional transverse CFRP U-wraps. This study proved that it is possible to quantify the higher flexural capacity of CFRP strengthened beams using external anchorage. OPEN ACCESS Fibers 2015, 3 540
Influence of Anchorage on the Behavior of CFRP RC Beams in Flexure
Engineering and Technology Journal
This research study involves experimental and theoretical investigations of the behavior of flexural debonding of carbon fiber reinforced polymer (CFRP) laminates with steel anchorages. A total of nine reinforced concrete beam specimens with cross section of (150mm width by 250mm height and 2000mm length) were investigated in this study to observe the flexural strength of each one. Eight beam specimens were strengthened with CFRP laminates and one beam specimen was tested without strengthening. The experimental results showed that the use of CFRP strips as external strengthening has significant positive effect on ultimate loads, crack patterns and deflections. The percent of increasing of the ultimate load capacity can be increased by about 65% when using two layers of CFRP strips instead of one layer. The ultimate load is increased by about 118% for the beams strengthened with bonded CFRP and external anchorage with respect to the reference beam. Three-dimensional nonlinear finite element analysis (i.e. ANSYS-version 9.0 computer program) is used to investigate the performance of reinforced concrete beams strengthened with CFRP. The comparison between the numerical and the experimental results asserted that good validity of the numerical analysis and the methodology developed in this study.
Role of U-shaped anchorages on performance of RC beams strengthened by CFRP plates
2008
Use of Carbon Fiber Reinforced Polymer (CFRP) Plates, as externally bonded reinforcement, is a practically efficient and technically sound method of strengthening and upgrading structurally inadequate or otherwise damaged or deteriorating Reinforced Concrete (RC) members. The ultimate capacity of the strengthened beam is controlled by either compression crushing of concrete, rupture of the composite plate, local failure of concrete at the plate end due to stress concentrations and flexural shear crack-induced debonding of Concrete-CFRP interface. Another factor that could affect the ultimate strength and mode of failure is the shear span. Beams with U-shaped anchorages were tested in four-point bending to determine the ultimate load carrying capacities and modes of failure of the beams. Properly placed U-shaped anchorages at plate cut-off points and along the span were shown to be effective in improving the performance of CFRP strengthened RC beams in flexure and shear by optimizing...
Flexural Behavior of RC Beams Strengthned with CFRP Sheets Using Different Strengthening Techniques
The Journal of Engineering Research, 2019
Due to the advantages of Fiber Reinforced Polymer (FRP) materials, they have been utilized to strengthen several reinforced concrete (RC) elements such as slabs, beams and columns. In this paper, five RC beams (200 mm width, 300 mm height, and 2750 mm length) were constructed. Four of these beams were strengthened with CFRP sheets whereas the last beam was used as a reference. Test parameters include the amount of FRP and the strengthening technique. Three strengthening techniques were used including the externally bonded technique (EB), the near surface mounted (NSM) technique using folded CFRP sheets inserted in near surface grooves, and a hybrid technique. All beams were tested under four point bending setup until failure. The control beam failed by the yielding of the tension steel followed by concrete crushing. The strengthened beams failed by steel yielding followed by either rupture or debonding of CFRP sheets at higher loads compared to the reference one. The stiffness after steel yielding and the ultimate capacity increased as the amount of CFRP increased. The strengthening technique affected the ultimate capacity of the strengthened beams. The NSM beam showed the lowest increase in the ultimate capacity (25.2%) whereas the hybrid beam showed the best performance with the highest increase in the ultimate capacity (58%) compared to the reference beam.
Influence of End Anchorage on Shear Strengthening of Reinforced Concrete Beams Using CFRP Composites
Current Science, 2017
The article presents an experimental study on the influence of various end anchorage systems on the shear strengthening of reinforced concrete (RC) T-beams using externally bonded fibre reinforced polymer (EB-FRP) composites. Two different end anchorage techniques namely self-end anchorage (SEA) and sandwich anchorage (SWA) were used. This study mainly focussed on evaluating the effectiveness of these anchorages to eliminate the conventional fibre reinforced polymer (FRP) debonding failure. A total of twelve R.C. T-beams with different strengthening techniques using CFRP including control beams were used. The test results show improved shear strength and better energy dissipation over conventional technique; this authenticates the influence of end anchorage and its effectiveness in improving shear resistance. Also, the enhanced FRP strain at failure proves that the anchorage employed improves the efficacy of FRP strengthening in terms of ductility and damage tolerance.
Flexural performance of CFRP strengthened RC beams with different degrees of strengthening schemes
2011
Externally bonded carbon fiber reinforced polymer (CFRP) composite laminates have been successfully applied to reinforced concrete (RC) beams and other structural elements for the purpose of increase load carrying capacity of such elements. This paper presents the experimental results on the flexural strengthening of reinforced concrete beams by CFRP laminates attached to the tensile soffit of the beams by epoxy adhesive.
Flexural Behavior of R/C Beams Strengthened with CFRP Sheets or Fabric
2002
The resistance to electro-chemical corrosion, high-strength to weight ratio, larger creep strain, fatigue resistance, nonmagnetic and non-metallic properties of carbon fiber reinforced polymer (CFRP) composites offer a viable alternative to bonding of steel plates in repair and rehabilitation of reinforced concrete structures. The objective of this investigation is to study the effectiveness of externally bonded CFRP sheets or fabric in increasing the flexural strength of concrete beams. Four-point bending flexural tests are conducted up to failure on nine concrete beams strengthened with different layouts of CFRP sheets and fabric, and three beams with different layouts of anchored CFRP sheets. An analytical procedure, based on compatibility of deformations and equilibrium of forces, is presented to predict the flexural behavior of beams strengthened with FRP sheets and fabric. Comparisons are made between the test results and the analytical calculations. Results of the testing showed that the flexural strength is increased up to 40% on beams strengthened with two layers of CFRP fabric, 49% for beams strengthened with two 1.42 mm thick CFRP sheets, and 58% on beams strengthened with two anchored 4.78 mm CFRP sheets.
Flexural strengthening for R.C. beams using CFRP sheets with different bonding schemes
Concrete Solutions 2014, 2014
An experimental program was performed through this research to assess the flexural strengthening capacity of reinforced concrete beams strengthened using CFRP sheets with variable end anchorage systems to enhance the bond between the CFRP sheets and concrete. Four point bending tests were performed on five R.C. beams, a control beam without strengthening, two beams strengthened with one and three layers of CFRP and bonded using only epoxy, and two beams strengthened with three layers of CFRP sheets using two different end anchorage systems. The proposed end anchorage systems increased the load carrying capacity of the beams by around 14% compared to the conventional bonding with epoxy, and changed the failure mode from debonding of the sheets to rupture of the sheets. The bottom reinforcement and the CFRP sheets showed a close load-strain behaviour, which indicates perfect bonding between the concrete substrate and the FRP sheets.