Fiber Reinforced Polymer Rods Research Articles

Nonlinear 3D Model of Double Shear Lap Tests for the Bond of Near-surface Mounted FRP Rods in Concrete Considering Different Embedment Depth

The utilization of near-surface mounted Fiber Reinforced Polymer (FRP) reinforcement as a method of strengthening in reinforced concrete structures has increased considerably in recent years. Moreover, the application of double-shear lap tests for this rein-forcement method leads to the achievement of a local bond-slip behavior in a bonded joint. This research, therefore, focused on 3-D modeling of this type of test to suitably characterize the bond mechanics between FRP rods and concrete at various embedment depth. The use of different alternatives to represent the interface between the FRP rod and concrete were analyzed after which a comparison was drawn between the numerical finite element (FE) simulations and experimental measurements. The results showed the prediction of the load–slip corresponded with the data obtained from the experiment. Finally, the proposed model has the ability to express the relationship between the penalty stiffness parameters in shear direction Kss = (Ktt) and the embedment depth of FRP rods.

Development of Optimal Anchor for Basalt Fiber–Reinforced Polymer Rods

Basalt fiber–reinforced polymer (BFRP) has been the most recent fiber–reinforced polymer (FRP) composite material introduced as reinforcement and prestressing tendons for concrete. Measuring the mechanical properties of BFRP rod/tendon is challenging using the existing mechanical testing methods due to their relatively lower transverse direction strength. Hence, gripping of the BFRP rods using the conventional wedge-type anchors becomes unsuitable because it causes stress concentration and exerts localized high transverse pressure on the specimen, which results in premature failure at the grips, instead of the desired rupture of the gauge section. This study is focused on the development of a new anchor for the prestressing of the BFRP rods based on using expansive cement as a grout material. The goal is to ensure a uniform distribution of pressure around the BFRP rods to avoid their failure within the wedge during prestressing. Pull-out tests were conducted on several samples with different anchor dimensions to study the interaction between the expansive cement and the BFRP rod. The parameters affecting the gripping behavior were investigated, and the design of the anchor was optimized based on finite-element simulations using commercially available software.

Acoustic Emission Signal Entropy as a Means to Estimate Loads in Fiber Reinforced Polymer Rods

Fibre reinforced polymer (FRP) rods are widely used as corrosion-resistant reinforcing in civil structures. However, developing a method to determine the loads on in-service FRP rods remains a challenge. In this study, the entropy of acoustic emission (AE) emanating from FRP rods is used to estimate the applied loads. As loads increased, the fraction of AE hits with higher entropy also increased. High entropy AE hits are defined using the one-sided Chebyshev’s inequality with parameter k = 2 where the histogram of AE entropy up to 10–15% of ultimate load was used as a baseline. According to the one-sided Chebyshev’s inequality, when more than 20% (k = 2) of AE hits that fall further than two standard deviations away from the mean are classified as high entropy events, a new distribution of high entropy AE hits is assumed to exist. We have found that the fraction of high AE hits. In glass FRP and carbon FRP rods, a high entropy AE hit fraction of 20% was exceeded at approximately 40% and 50% of the ultimate load, respectively. This work demonstrates that monitoring high entropy AE hits may provide a useful means to estimate the loads on FRP rods.

Predicting multi-axial diffusion of water in laminated composite structural components

This study examines the diffusion of water in fiber-reinforced polymer (FRP) laminated composites, comprising epoxy resin and unidirectional glass fibers, at different material and structural scales. Experiments on the diffusion of neat resin, FRP laminas in the axial and transverse fiber directions, FRP laminated composites with different stacking sequences, and FRP plates, rods, and pipes are conducted to obtain the diffusion processes at different length scales. Simultaneously, a diffusion model for a laminated composite is formulated to mathematically describe the multi-axial diffusion processes in FRP composites at various length scales, i.e., single lamina, laminated stacking sequence, and component. The study shows that the diffusivity constants calibrated from neat epoxy resin and unidirectional laminas are adequate to predict the diffusion responses of laminated composite systems and structural components of larger sizes. This capability is useful in predicting the long-term diffusion responses of FRP composites of complex geometries and large sizes where conducting diffusion tests on such systems is not feasible.

GFRP Reinforcement Behaviour under Multi-Axial Stress - Experimental Study

This paper is focused on the design of concrete structures reinforced with modern composite material – Fibre Reinforced Polymer (FRP) reinforcement. It presents actual results from the testing of FRP rods under a simultaneous tensile and shear loading. The results were experimentally obtained on specimens of Glass Fibre Reinforced Polymer (GFRP) reinforcement. The text also points out that the widely used fib Bulletin no. 40 technical report does not provide sufficiently reliable formulas and may overestimate the load-bearing capacity of the element. Therefore, the conclusions formulated are primarily concerned with their practical use in the design of this modern material.

Evaluation of a new bond-type anchorage system with expansive grout for a single FRP rod

Prestressed concrete applications require a high strength prestressing material that could apply and maintain effective compressive force to concrete members. Although fiber reinforced polymer (FRP) materials, especially carbon FRP (CFRP), have the desired strength, no efficient system for its anchorage to concrete has been devised yet. This paper presents an experimental evaluation on a new bond-type anchorage system using an expansive grout as a filling material to anchor CFRP rods. A total of twelve specimens were fabricated and tested. Short-term and long-term pullout tests were performed. The CFRP rods were 0.375 in. (10 mm) and 0.50 in. (13 mm) in diameter. The parameters investigated were the bond length, rod diameter, and curing time of the expansive grout. The experimental results showed that 12 in. (305 mm) and 15 in. (381 mm) were adequate bond lengths to effectively anchor the 0.375 in. (10 mm) and 0.50 in. (13 mm) CFRP rods, respectively. The results also indicated that the anchor strength and stiffness were directly proportional to the bond length, and cross-sectional area ratio of CFRP rods to anchor borehole affected the stiffness and bonding capacity of the proposed anchor. Finally, a numerical analysis was carried out to predict the tensile behavior of FRP anchors. The numerical results had good agreement with the experimental results.

FE stress analysis and prediction of the pull-out of FRP rods glued into glulam timber

ABSTRACT This paper focuses on the FE analysis of the mechanical behavior of glued composite fiber-reinforced polymer (FRP) rods into glulam timber, using a 3D-continuum damage mechanics. The application of FRP to the glulam timber beams, despite the fact of limited investigations to date, offers an interesting and economic solution for strengthening in timber construction. In particular, the use of glued-in FRP rods for timber connections instead of steel is of great interest, due to the improved durability of the joint systems compared to their equivalent counterparts made of steel rods. For pull-out tests, the estimation of the mechanical response of glued FRP rods into glulam timber is very complex because of the combination of the three different materials: FRP rods, epoxy resin and glulam timber as well as the complexity of the expected brittle modes of failure of the timber. On the other hand, the existing prescriptive approaches (standard design codes) did not cover all the modes of failure expected within timber material and their predictivity is highly depending on the loading direction and on the rod material. There is, therefore, still a need to establish a general and predictive FE model to simulate accurately and cost-effectively the glued-in rod timber connections. In this study, a FE model combining 3D continuum damage mechanics (CDM) and cohesive zone modeling approaches is presented and its effectiveness was verified by comparison to experimental results available in the literature.

Development of finite element model for embedded carbon fiber–reinforced polymer rod in reinforced concrete frame joints

The stiffness and strength of joints are the main factors in providing stability and ductility of a structure during dynamic load such as earthquake. In the high-humidity areas, the reinforcement is exposed to corrosion, which commonly occurs in the joints, due to the presence of micro-cracks in the joints, shrinkage or other concrete casting issues. Therefore, one of the main failure mechanisms of building during an earthquake is caused by damage in the joints in humid areas. This is mainly caused by corroded steel reinforcement, which reduces functionality of the frame joints in transferring the loads. This study proposes a new design for reinforced beam–column joints with embedded carbon fiber–reinforced polymer rods, which possesses extremely high strength and resistance against corrosion and high stiffness. The finite element model for embedded carbon fiber–reinforced polymer in the joints was developed in order to evaluate the performance of the proposed joints during earthquake execution. The developed program was verified through an experimental test on reinforced concrete frame subjected to vibration using dynamic actuator. The finite element program was implemented for one-story reinforced concrete frame and two-story frame building with proposed joints and seismic analysis. The results demonstrated a significant improvement in the performance of the frames reinforced with embedded carbon fiber–reinforced polymer in joints in terms of lateral load resistance capacity and failure mechanism.

Strengthening of Reinforced Concrete Beams using Near-Surface Mounted Fiber Reinforced Polymer Rods

Strengthening of Reinforced Concrete Beams using Near-Surface Mounted Fiber Reinforced Polymer Rods

Iron-based shape memory alloy and fiber reinforced polymers rods for prestressed NSM strengthening of RC beams

Abstract The present study involves flexural strengthening of reinforced concrete (RC) beams by prestressed fiber reinforced polymers (FRP) and iron-based shape memory alloys (Fe-SMAs) using the near surface mounted (NSM) technique. ANSYS nonlinear finite element analysis (FEA) software was employed to model RC beams which were validated using the data from an existing experimental study in the literature. Parameters considered were rod length and NSM rod material type under three prestressing levels 20, 30 and 40%. The influence of these parameters on the beams’ load carrying capacity, midspan displacement, ductility index, and failure mode were determined. The results showed that at higher levels of rod prestressing, cracking, yielding, and ultimate load capacities of the beam were improved. However, the displacement was decreased and consequently, the ductility index reduced as prestressing level increased. Furthermore, the Fe-SMA material was able to provide significant ductility. The optimum prestressing level could be identified based on the primary RC beams’ design criteria to either improve load or displacement capacity or both.

Alkaline Attack on Cement or Lime Mortar and Glass Fiber-Reinforced Polymer Rods

Alkaline Attack on Cement or Lime Mortar and Glass Fiber-Reinforced Polymer Rods

Embedded carbon fiber-reinforced polymer rod in reinforced concrete frame and ultra-high-performance concrete frame joints

Beam–column joints play an important role in providing lateral stiffness and integrity of frames during dynamic loading such as earthquake. In the high humidity areas, during functioning of the building cracks occur, which leads to the corrosion of the reinforcement due to the environmental exposures. Therefore, one of the main failures mechanism of building during an earthquake is caused by easily yielding of corroded steel reinforcement, which leads to reduce functionality of the frame joints in transferring the loads. This study proposed a new design to reinforce the beam-column joints with embedded carbon fiber-reinforced polymer (CFRP) rods, due to their extremely high strength and stiffness, along with the fact that they will not rust or corrode and very light weight. CFRP rods are used in reinforced concrete (RC) frame and ultra-high-performance concrete (UHPC) frame subjected to dynamic load. The prototype of the proposed design is constructed as frame with conventional concrete and frame with UHPC material to conduct experiments Test as well as numerical analysis to evaluate the performance of the proposed joints under dynamic loads. The results showed improvement in the performance of the frames reinforced with embedded CFRP in joints in terms of lateral load resistance capacity, ductility behaviour, overall stiffness, and failure mechanism.

Numerical simulation of the debonding process in pull-out tests of near-surface mounted FRP rod in concrete

Purpose Near-surface mounted (NSM) fiber-reinforced polymer (FRP) rod is extensively applied in reinforced concrete (RC) structures. The mechanical performances of NSM FRP-strengthened RC structures depend on the bond behavior between NSM reinforcement and concrete. This behavior is typically studied by performing pull-out tests; however, the failure behavior, which is crucial to the local debonding process, is not yet sufficiently understood. Design/methodology/approach In this study, a three-dimensional meso-scale finite element method considering the cohesion and adhesion failures is presented to model the debonding failure process in pull-out tests of NSM FRP rod in concrete. The smeared crack model is used to capture the cohesion failures in the adhesive or concrete. The interfacial constitutive model is applied to simulate the adhesion failures on the FRP-adhesive and concrete-adhesive contact interfaces. Findings The present method is first validated by two simple examples and then applied to a practical NSM FRP system. This work studied in detail the debonding process, the bond failure types, the location of peak bond stress, the transmitting deformation in adhesive and the morphology of contact zone. The developed method provides a practical and convenient tool applicable for further investigations on the debonding mechanism for the NSM FRP rod in concrete. Originality/value A three-dimensional meso-scale finite element method considering the cohesion and adhesion failures is presented to model the debonding failure in NSM FRP-strengthened RC structures. The smeared crack model and the interfacial constitutive model are introduced to develop a convenient approach to analyze the failures in adhesive, concrete and related interfaces. The developed numerical method is applicable for studying the debonding process, the bond failure types, the location of peak bond stress, the transmitting deformation in adhesive and the morphology of contact zone in detail.

Experimental study of Z-pin fatigue; understanding of mode I and II coupon behaviour

Insertion of carbon fibre reinforced polymer rods (Z-pins), is an effective method for the through-thickness reinforcement (TTR) of laminated composites. Whilst Z-pins are primarily used to mitigate delamination under quasi-static loading and/or impact events, the effectiveness of TTR following long-term exposure to cyclic loads still needs to be properly understood. This paper aims to fill the aforementioned knowledge gap by addressing the effect of fatigue on the Z-pins themselves, both in mode I and mode II regimes. The fatigue tests considered here are carried out on single Z-pin coupons, as well as Double-Cantilever-Beam (DCB) and End-Loaded-Split (ELS) specimens. The results indicate that, for relatively small cyclic displacements, Z-pins tolerate fatigue well, exhibiting good residual performance post-fatigue. However, increasing the amplitude of the fatigue loads damages the Z-pins and, hence, it tends to reduce the TTR residual ability to mitigate delamination under further quasi-static or impact loading.

Experimental investigation on the ball burnishing of carbon fiber reinforced polymer

ABSTRACTThe polymer-based materials are generally used in all industrial applications. Even if polymer bars can be machined easily, they need surface finishing treatment after the machining process. The ductile properties make coarse roughness on the surface that causes the elastic structure of polymer materials. The carbon fiber reinforced composite materials differ from polymer-based materials by high strength and stiffness. Its structure exhibits similar performances such as metallic materials. The effect of ball burnishing on the surface quality of rod workpiece was investigated in this study. To enhance the surface quality of high strength carbon fiber reinforced polymer rod workpiece, burnishing process was performed in three different parameters (force, feed rate, number of passes) and under four different mediums (dry, wet, boron oil, and mineral oil) conditions. The results of the experiments were analyzed, and optimum burnishing parameters were determined and discussed in detail. The best surface roughness value of the CFRP material used in the experiments was obtained as burnishing force: 250 N, feed rate: 0.05 mm/rev, four passes and wet medium. According to the results of variance analysis, it was found that the CFRP workpiece is the important leading factor for surface roughness with a contribution ratio of 62.47%.

A Parametric Study on the Flexural Strengthening of Reinforced Concrete Beams with Near Surface Mounted FRP Bars

FRP rods as lightweight materials with extraordinary properties of high strength to weight ratio, corrosion resistance, potentially high overall durability, tailor ability and high specific attributes are one of the most favorable materials to strengthen existing reinforced structures. The present study aimed to identify the behavior of reinforced concrete flexural beams strengthened with fiber reinforced polymer (FRP) rods through near surface mounted method (NSM). The results of the current study were based on nonlinear finite element software ABAQUS which can accurately simulate the experimental investigations on flexural behavior of reinforced concrete beams strengthened with NSM FRP rods. Validation of the proposed model was confirmed first by making a comparison with the experimental study presented in the literature. A parametric analysis was conducted on validated specimens to investigate the effect of FRP rod diameters, rod arrangements, FRP materials, as well as rods groove intervals on flexural behavior of strengthened reinforced beams. The numerical results of mid-span bending moment deflection, ultimate bending moment, failure deflection and ductility index were reported. For the sake of simplicity to be used by engineers, the results of the current study were drawn in the form of design charts and tables.

Experimental study on RC beams strengthened with CFRP rod panels

Externally bonded (EB) fiber reinforced polymer (FRP) laminates and fabrics have become a mainstream method for retrofitting and upgrading concrete structures. Nevertheless, when strengthening long-span members or members with limited access, labor, traffic, and equipment demands may hinder the use of continuous EB FRP. The use of carbon FRP (CFRP) rod panels is a recent application of FRP material intended to overcome the above limitations. CFRP rod panels are developed from small diameter rods and are made continuous by means of a finger joint. This study leveraged four-point bending tests to determine whether spliced CFRP rod panels can effectively serve as flexural reinforcement for concrete members. Testing included a control beam and beams strengthened with the following FRP reinforcement layouts: (1) continuous rod panel, (2) spliced panel (two half-length panels with a 150 mm finger joint), (3) spliced panel anchored at ends with CFRP fabric, (4) continuous CFRP laminate, and (5) lap-spliced CFRP laminate system. Beams bonded with either continuous or spliced rod panels failed by concrete cover separation. The beam with spliced and anchored rod panel failed by intermediate crack-induced debonding of the panel. No local debonding or other signs of distress were observed at the finger joint for the two beams strengthened by spliced rod panels. For beams bonded with continuous and lap-spliced CFRP laminates, the failure was by laminate debonding. Compared to a control specimen, the maximum load increase of the strengthened beams was as follows: 112% for the continuous rod panel; 106% for spliced rod panel; 158% for the spliced/anchored rod panel; 49% for continuous laminate; and 31.8% for lap-spliced laminate.

A theoretical solution for the pullout properties of a single FRP rod embedded in a bond type anchorage

ABSTRACTThis paper proposes a theoretical solution for predicting the pullout properties of a single fiber-reinforced polymer (FRP) rod embedded in a bond type anchorage based on a trilinear bond–slip model. The radial variation of the shear stress and reaction of the steel sleeve are considered in the solution. Pullout procedure with elastic, elastic-softening, elastic-softening-debonding, pure softening, softening-debonding, and debonding stages, as well as the corresponding critical stages, are analyzed. In this theoretical solution, the maximum pullout load, shear stress along the rod–grout interface, axial tensile stress of the FRP rod, and load–slip relationship are derived with explicit formulations. Effective bond length of bond type anchorage is also discussed. The solution is validated against experimental results available in literature. The theoretical solution reveals that the anchorage may attain its maximum pullout load in the elastic-softening, pure softening, or elastic-softening-debonding stage. Moreover, the effects of embedded length, ultimate shear stress, and residual shear stress on maximum pullout load closely related with the stage in which the anchorage attains its maximum pullout load. However, the effect of radius of FRP rod on the maximum pullout load increases with the embedded length, no matter in which stage the anchorage attains its maximum pullout load.

Bond-shear Behavior of FRP Rods as a Function of Attachment Configuration

The use of external reinforcement to improve or enhances the flexural capacity of a member depends on the transfer capacity, and the failure behavior of the composite between the reinforcement, the epoxy resin and the concrete. The most influencing factor is the bond-shear capacity between the rod and the epoxy, and the epoxy to the concrete. Fiber Reinforced Polymer (FRP) rods are the latest alternate for fulfilling the external reinforcement scheme. In the field, the mandated embedment depth as outlined by the ACI 440 code, could customary not be achieved since factors such as the depth of the concrete cover, and presence of stirrups limits the space. This study is aimed to evaluate the effect of FRP rod configurations with respect to the concrete surface, to the effectiveness of external reinforcement. The study looked into the bond-shear capacity as well as the mode of failure, influence by the rod attachment depth. It was shown that the embedment depth significantly influenced the failure mode, and therefore the strain transfer capacity from the concrete to the rods.

Study of FRP bars under tension using acoustic emission detection technique

Acoustic emission (AE) signal has proved to be a useful tool for monitoring structures reinforced with FRP composites such as Fiber Reinforced Polymer (FRP) reinforced beams, carbon FRP (CFRP) sheets, or steel fiber reinforced concrete. This work focuses on studying the behavior of pultruded FRP bars, which have been manufactured using continuous fibers. Different configurations of CFRP and glass FRP (GFRP) bar specimens subjected to tensile load were monitored using AE technique. Several algorithms were used for signal processing to analyze AE signals in the time domain and in the time–frequency domain. The signal processing techniques extracted the amplitude, cumulative events, duration, energy, rise time, number of counts, cumulative counts, and frequency peaks of the acoustic signals. The frequency maxima were determined for different amplitude signals using short-time Fourier transform (STFT). Cumulative counts of AE signals showed significant changes in the slope during the tension test, while the stress–strain relationship of the FRP rods showed virtually no deviation from linearity. CFRP bars recorded higher amplitude signals and lower duration, than GFRP bars. The acoustic emission characteristics presented in this work show strong correlations with ultimate load and may prove useful for damage prediction.