CFRP Sheets Research Articles

Structural Behavior of RC Beams Containing Unreinforced Drilled Openings with and without CFRP Strengthening.

Construction deficiencies can cause serious problems that significantly decrease the design strength of concrete structures, such as the unreinforced drilled openings. With the absence of sufficient reinforcement, the stress concentrations generated around the opening corners produce cracks in the beams. The size and location of the opening significantly affect the behavior of the beam under static and dynamic load. In this work, an experimental and numerical program was performed to investigate the behavior of drilled reinforced concrete beams with and without strengthening using CFRP sheets. Energy absorption and SDOF analyses were performed to preliminary assess the behavior of the beams under the dynamic load, such as blast. One control beam without any openings, six beams with tension-zone openings, and six beams with shear-zone openings were tested. It was found that the samples with tension-zone openings were slightly affected by the opening, where the reduction in the ultimate strength was approximately 7 to 14%. The beams were able to recover up to 46% of the lost strength by CFRP strengthening. On the other hand, the shear-zone opening significantly decreased the strength and energy absorption and increased the blast response. It can be concluded that it is not recommended to drill any opening at the shear zone as strength loss can reach 57% even with the strengthening, especially for blast resisting structure; in addition, the strength recovered from approximately 11.95 to 32.46% only. The finite element model was able to predict the strength of the beams. The results were closer in the case of tension-zone opening than those in the case of the shear-zone opening. Shear cracks were observed at the corners of the openings even if the opening exists at the tension zone. A reduction in the density of cracks can be observed after the strengthening, where the FRP sheet decreases the stress in the concrete.

Theoretical analysis and experimental research on the pressing force of robot drilling CFRP sheet

Theoretical analysis and experimental research on the pressing force of robot drilling CFRP sheet

Influence of Coarse Aggregate Size on the Bonding between CFRP Sheets and Metakaolin-Based Geopolymer Concrete and Ordinary Concrete

Influence of Coarse Aggregate Size on the Bonding between CFRP Sheets and Metakaolin-Based Geopolymer Concrete and Ordinary Concrete

The Effect of Rebar Embedment and CFRP Confinement on the Compressive Strength of Low-Strength Concrete

Low-strength concrete (LSC) elements are prone to several seismic and static loads and are one of the priorities to be considered for FRP strengthening. However, certain provisions should be taken into account according to provisions, as elements with considerably low compressive strength are not eligible for FRP confinement. This experimental study investigates (1) the effect of rebar planting on increasing the initial compressive strength of LSC to achieve allowable compressive strength for FRP strengthening, and (2) the effect of CFRP confinement on increasing the strength of rebar-embedded specimens and determining the most effective factor for strength improvement. For this purpose, 38 standard concrete cylinders were tested under compressive load. The variables of this study were rebar length and diameter, the compressive strength of concrete, and the number of CFRP sheets. Two initial compressive strengths below the designated compressive strength of 17 MPa (12.5 and 14.5 MPa) were selected. After determining rebar-reinforced specimens with compressive strength of more than 17 MPa, CFRP confinement and compressive tests of these cylinders were utilized. A statistical single-factor ANOVA analysis is performed to determine the most effective variable for ultimate strength and strain, individually. In the end, available models in the literature were utilized to predict experimental data. The results indicated the effectiveness of rebar planting for strength enhancement up to 53%, also showing that specimens with initial compressive strength of 14.77 MPa were suitable for CFRP confinement after rebar planting. The experimental and statistical ANOVA results demonstrated the CFRP confinement and its interaction with rebar embedment as the most effective factors with respect to increasing the load-bearing capacity of LSC concrete.

Re-evaluation of shear contribution of CFRP and GFRP sheets in concrete beams post-tensioned with unbonded tendons

Contemporary design guidelines for the shear resistance of post-tensioned concrete (PC) beams retrofitted with fibre reinforced polymer (FRP) sheets are developed from the results of reinforced concrete (RC) beams. The accuracy of these guidelines for calculating the shear resistance of PC beams wrapped with FRP sheets is still questionable due to the difference in the shear behaviour of RC vs PC beams. The effects of the essential factors (e.g. tendon profile and anchorage system) on the shear resistance of PC beams have not been sufficiently studied, particularly for unbonded post-tensioned concrete (UPC) beams. This study presents an experimental investigation on the shear behaviour of UPC T-beams and the shear contribution of CFRP/GFRP sheets. The experiment consisted of 26 large-scale UPC T-beams with various factors including the tendon profile (harped or straight), concrete strength, FRP anchors, CFRP vs GFRP sheets, and various wrapping configurations. The experimental results showed that CFRP/GFRP sheets increased the shear resistance of UPC beams by 4–26%, which was much lower than that in RC beams. In comparison with the UPC beams with straight tendons, those with harped tendons exhibited a reduction in the shear contribution of CFRP/GFRP sheets (approximately 40%) and showed a more ductile failure mode with an improvement of the beam deformation (up to 2.3 times). FRP anchorage systems significantly enhanced the FRP shear contribution and energy absorption increased by 88% and 42% regarding those without anchors, respectively. Besides, it was observed from the test data that the widely-used method to determine the experimental shear contribution of FRP sheets in PC beams based on the difference between the shear resistance of strengthened and unstrengthened beams was inappropriate because it failed to consider the interactions between FPR sheets and other shear components, i.e. concrete and stirrups. Meanwhile, the experimental shear contribution of FRP sheets is recommended to be determined from the actual strain data of the FRP sheets across the main shear crack.

Comparative Seismic Behavior the Retrofit of 60year Old Hospital between CFRP Materials and Concrete Walls by Nonlinear Static Analysis

The Casimiro Ulloa Hospital is a confined masonry structure more than 60 years old that does not satisfy the requirements of the Peruvian seismic code E.030 and it is located at high seismic zone. Therefore, this hospital is susceptible to collapse and becomes an essential deficient structure. Therefore, the present study is based on a comparative analysis between reinforced concrete wall and CFRP sheets through the nonlinear Push Over method in order to obtain which is the best reinforcement in structural capacity. The reinforcement with eight L-shaped concrete walls of 15 cm thick located at the corners of the structure, increased the strength of the hospital by 115% in longitudinal direction (Axis X) and 108% in transversal direction (Axis Y), and also increased the ductility by 3% and 117% in the directions respectively. The other reinforcement was carried out with CFRP sheets and anchors. The sheets were designed with a width of 9 inches and were placed in an X-shape in the masonry load-bearing walls and the anchors were implemented in the corners of the laminate walls in order to ensure adequate load transfer between the sheets and the surface. This reinforcement increased the strength of the structure by 345% in axis X and 150% in axis Y and increased the ductility by 59% in longitudinal direction and 331% in transversal direction.

Flexural behavior of beams reinforced by GFRP bars with CFRP sheets immersed in epoxy as shear

Corrosion in steel bars is considered a big problem because corrosion is mainly responsible of decrease virtual age of structures and many risks indicated by deterioration. In addition, corrosion increases the cost of maintenance, particularly structures exposed to harsh environmental condition. FRP bars (Fiber Reinforced Polymer) became an alternative material from traditional steel bars. FRP had properties made it used in civil engineering sectors which are lightweight, non-corrosive, non-conductive made it a preferred alternative from steel bars in aggressive environments. FRP bars don’t have yield made it con not bind outside its linear behavior to make ties, because of the brittle behavior of FRP bars up to failure. So that, the new innovative manner by using CFRP sheets stirrups immerged by sikadur330 for produce beams can resist the harsh condition and purely reinforced with FRP in a new manner can provide stirrups in full different sizes and with lower cost. Twelve beams reinforced with GFRP bars in three different ratios of tension reinforcement (four beams for each ratio). Three control beams with steel stirrups: two beams were designed to fail in shear. Whilst, the residual nine beams with shear reinforcement made from CFRP sheets strips, immerged by sikadur330. The main variable were studied is the change in type and amount of secondary reinforcement and change in amount of primary reinforcement. The test was conduct under four point loading and in simply supported conditions. The result of tested beams illustrated that, beams had a higher percentage of tension reinforcement and shear reinforcement displayed an increasing in ultimate load about 38.1% from related control beam. While, an equivalent amount of shear reinforcement displayed an increasing in carrying load capacity up to 10%. In maximum ratio of CFRP sheets immerged by sikadur330 stirrups convert failure mode from shear to flexural indicated by crushing in cover of concrete. In addition, increased energy absorption, changed cracks orientation, increased energy absorption, decrease principal strain and increased concrete tensile.

Rehabilitation of partially damaged high strength RC corbels by EB FRP composites and NSM steel bars

In this study, a comparison has been done between the efficiency of repairing of partially damaged high strength self-compacting RC corbels using two techniques, namely are NSM steel bars and CFRP sheets. The experimental program consists of testing eleven specimens, one of which acted as a control corbel (without repairing) and the other ten are upgraded using several configurations of alignment with two damage levels (45% and 65%). The response has been discussed in terms of the first cracking load, ultimate load, maximum deflection, failure mode, loading history, crack pattern, toughness value, and ductility index. Results revealed that the NSM steel bars technique could be adopted as an adequate method within the early levels of damage whereas the EB CFRP sheet is more suitable for largely damaged corbels. Moreover, results revealed that NSM technique with the inclined, horizontal, and combined alignment yielded enhancements in ultimate load capacity of 98.6%, 55.1% and 74.2%, respectively for a damage level of 45% and 24%, 50% and 19% for damage level of 65%, respectively. Whereas, the corresponding improvement using the CFRP sheet with damage level of 45% are 52% and 50% for specimens repaired using horizontal and diagonal CFRP sheet, respectively. The respective values are 71%, 38% for damage level of 65%.

Finite Element Analysis of Reinforced Concrete Beams Strengthened with Carbon Fiber Reinforced Polymer Sheets

This paper presents outcomes of extensive research conducted to study the behavior of reinforced concrete (RC) beams strengthened with CFRP sheets and subjected to shear and flexural loading. A 3-dimensional Finite Element(FE) modelling was carried out using ABAQUS software program to simulate the flexural and shearing behavior of a number of RC beams strengthen with CFRP. Moreover, the results of the numerical simulation were compared with actual results of experimental physical modelling of RC beams subjected to the same loading conditions for validation purpose.Appreciable number of sets of control RC beams and CFRP strengthened RC beams for flexural and shear were investigated. All beams were rectangular in cross section. To accurately describe the behavior of these tested RC beams, different material constitutive models were used in the simulation. Concrete damaged plasticity model was used to model concrete;a linear elastic perfectly plastic model was used to model both reinforcing steel and stirrups, while a linear elastic isotropic model was used to simulate the behavior of CFRP material. Moreover, the interface between concrete and CFRP material was accounted for and was simulated using a tie perfect bond model while steel reinforcement is bonded with concrete as anembedded element in ABAQUS. A careful comparison between the results of the experimental tests and those of the numerical simulation showed that the proposed FE model is able to describe the behavior of reinforcedconcrete beams strengthened with CFRP in terms of crack pattern and load deflection curves to an appreciable level of accuracy. Generally, the results demonstrate that numerical approach can be used to deeply investigate thebehavior of RC beams strengthened with CFRP sheets. It was also concluded that the numerical approach was able to capture significant aspects of structural behavior of the tested beams such as strain distribution in CFRP, which is often not easily captured experimentally or analytically.

Efficient bidirectional U-wrap system to anchor CFRP sheets bonded to reinforced concrete T-girders

Externally bonded fiber reinforced polymers (FRP) has been established to be an effective method for strengthening reinforced concrete beams, especially when it is properly anchored so that the premature debonding failure mode is avoided. In this study, five reinforced concrete T-girders were constructed, with the first girder being a control specimen. The remaining four girders were then strengthened with one CFRP sheet. One of them was tested without anchorage while the other three beams had the CFRP sheet anchored with various configurations and amounts of ± 45° bidirectional glass FRP U-wraps. The goal of the experimental program was to evaluate the performance of the anchorage systems in order to compare the flexural strength to that of the unanchored and control specimens. Also, the comparison of the different U-wrap configurations was determined to address the most effective layout. The experimental program allowed concluding that the three anchored girders showed increase in flexural strength when they were compared to the control and unanchored girders. Furthermore, the anchored girders reached similar capacities so the configuration with the lowest amount of ± 45° bidirectional glass FRP U-wraps was the most efficient.

Experimental investigation on the behaviour of flexural strengthening of beams using carbon fibre reinforced polymer sheet

Externally bonded fibre reinforced polymer sheets have been proven to be useful for strengthening and repairing RCC beams. The use of carbon fibre unidirectional fabric to strengthen RC cube, cylinder, and flexural beams is being tested. Externally reinforced concrete beams with epoxy-bonded fabric were put to the test to failure using a symmetrical one point focused static loading method. The concrete mix grade was M30, and the steel grade was Fe500. 12 cubes, a cylinder, and four RC beams have been casted. The beam is meant to be doubly reinforced, with a dimension of 1000 * 150 * 150 mm and tension and compression steel of 10 mm. Stirrups are made of 8 mm diameter bars. It comprises of one control beam and three 75 percent ultimate load preloading in the control beam. Following the testing process, the beams will be strengthened with CFRP sheet in various amounts. The pre-damaged beams and the CFRP sheet are joined together using epoxy resin. Flexural tests were run on the strengthened beams to ascertain their ultimate load carrying capacity. Using experimental data, it was determined how many CFRP layers affected each beam's load, deflection, and failure modes.

Cyclic performance of exterior R.C beam-column strengthened with different thicknesses of CFRP sheets

The recent ground motion results indicated that the RC buildings are required to be retrofitted by different strengthening techniques. Nowadays, the external strengthening gain interest since its easy, cost effective and not required redesign of buildings. The CFRP sheets are suitable solution and utilized by a number of researchers. However, the numerical cyclic performance of connection strengthened with different thicknesses of CFRP need to be well investigated. This study assessed the performance of RC exterior beam column connection strengthened with CFRP sheets First, two grades of concrete are utilized to be control specimens, normal concrete compressive strength (C20) and high concrete compressive strength (C50) then, the specimens are retrofitted with different thicknesses (1.2, 2.4, 3.6mm) of CFRP sheets. The stresses and damage states showed the importance of connection retrofitting. The CFRP shift the plastic hinge zone away from the panel zone. Furthermore, the results demonstrated that by increase of CFRP thickness the connection resistance will be improved. The comparison between the hysteresis curves demonstrated that the yield and ultimate loading were enhanced for strengthened connection for both concrete grades and the incremental in thicknesses also increase them. The outputs also exhibited that the stiffness and ductility has increased for retrofitted specimens indicating that the CFRP comprehensively overcome the applied cyclic loading and the beam column connection is able to resist such type of loading.

Shear Behavior of Reinforced Concrete Beams Repaired Using a Hybrid Scheme with Stainless Steel Rebars and Cfrp Sheets

Shear Behavior of Reinforced Concrete Beams Repaired Using a Hybrid Scheme with Stainless Steel Rebars and Cfrp Sheets

Novel Method for Strengthening Insufficient Steel Reinforcement Splice Using CFRP Sheets

Novel Method for Strengthening Insufficient Steel Reinforcement Splice Using CFRP Sheets

Numerical Analysis of Tensile Performance of Central Cracked Steel Plates Repaired with CFRP Sheets

Numerical Analysis of Tensile Performance of Central Cracked Steel Plates Repaired with CFRP Sheets

Nonlinear seismic analysis of composite coupled shear walls strengthened by CFRP sheets

Nonlinear seismic analysis of composite coupled shear walls strengthened by CFRP sheets

Strengthening of RC Beams using Steel Plate-Fiber Concrete Composite Jackets (Finite Element Simulation and Experimental Investigation)

In this research, steel plate-fiber concrete composite jackets (SPFCJ) was used to strengthen the RC beams. The accuracy of the analysis method was evaluated by modeling RC beams fabricated in the laboratory, and a good agreement was observed. Variables in the finite element method (FEM) analysis include the strength class of concrete used in the main beam (15, 20, and 25 MPa), the beam length (1.4 and 2.8 m), the type of jackets (RC jacket, SPFCJ, and CFRP sheet), and jacket thickness (40, 60 and 80 mm). SPFCJ is effective for all three concrete grades and increased the energy absorption capacity by 1.88, 2.07, and 2.25 times, respectively. The bearing capacity of the strengthened beam with 60 mm composite jackets increased by 79 and 20% more than the values corresponding to jackets with 40 and 80 mm thickness. The jacket thickness parameter significantly influences the response of strengthened beams with the proposed composite jackets. Depending on the dimensions and geometric characteristics of the beam, the appropriate thickness for the jacket should be considered, and increasing the thickness can not always improve the beam bearing capacity.

Rehabilitation of Hybrid RC-I Beams with Openings Using CFRP Sheets

This research presents an experimental investigation of the rehabilitation efficiency of the damaged hybrid reinforced concrete beams with openings in the shear region. The study investigates the difference in retrofitting ability of hybrid beams compared to traditional beams and the effect of two openings compared with one opening equalized to two holes in the area. Five RC beams classified into two groups, A and B, were primarily tested to full-failure under two-point loads. The first group (A) contained beams with normal weight concrete. The second group (hybrid) included beams with lightweight concrete for web and bottom flange, whereas the top flange was made from normal concrete. Two types of openings were considered in this study, rectangular, with dimensions of 100×200 mm, and two square openings with a side dimension of 100 mm. A full wrapping configuration system for the shear region (failure zone) was adopted in this research. Based on the test results, the repaired beams managed to recover their load carrying capacity, stiffness, and structural performance in different degrees. The normal concrete beam regains its total capacity for all types of openings, while the hybrid beams gain 84% of their strength. The strength of hybrid concrete members compared with normal concrete is 81 and 88% for beams of one opening and two openings, respectively. Doi: 10.28991/CEJ-2022-08-01-012 Full Text: PDF

Novel method for strengthening insufficient steel reinforcement splice using CFRP sheets

Novel method for strengthening insufficient steel reinforcement splice using CFRP sheets

Study on strengthening effect of prestressed cfrp sheet on steel box girder

The finite element software Abaqus is used to simulate the reinforcement of the steel box girder with CFRP sheets. The wave anchor anchorage system clamps the carbon fiber (CFRP) sheets and anchors them in the tensile zone at the bottom of the steel box girder. The temperature method is used to simulate the prestress applied to the steel box girder in the actual project, and the stress of the steel box girder in the project example is compared to analyze the mid span deflection of the steel box girder; With the change of stress and strain, the mid span deflection of prestressed CFRP sheet to steel box girder is analyzed; Stress; The improvement of strain sum shows that prestressed CFRP has good reinforcement effect for flexural members.