Fiber Reinforced Polymer Rods Research Articles

XGBoost algorithm based estimation of near surface mounted FRP rod-to-concrete bond strength and failure mode

Using fiber-reinforced polymer (FRP) in reinforced concrete (RC) structures can mitigate the colossal repair costs due to reinforcing steel corrosion. Hence, FRP rod/bar is gaining wider applications in diverse RC structures as a partial or full replacement for steel rebar. The FRP rod-to-concrete interfacial bond is pivotal in transferring stresses from concrete to FRP rods. This study develops a novel prediction model to estimate the near surface mounted FRP rod-to-concrete bond strength as well as the failure type using five machine learning (ML) algorithms, namely, linear regression, decision tree, gradient boosting tree, random forest, and extreme gradient boosting (XGB). The performance of the developed models was compared with that of four bond strength design guidelines and one analytical model. A database comprising 416 experimental datasets was constructed and used for model training and validation. Based on statistical performance metrics, the precision of the XGB algorithm was superior to that of the other ML models, design guidelines, and analytical model. Feature importance analysis based on the SHapley Additive exPlanations theory and partial dependence plot was performed. The results show that the bond length had the most significant influence on the bond strength, followed by the tensile strength of the FRP composite, diameter of the FRP rod, compressive strength of concrete, and elastic modulus of the FRP composite. A graphical user interface was developed and offers a user friendly, free access, and simple tool for estimating the bond strength and failure type of FRP rods in concrete.

Experimental Investigation into the Flexural Behaviour of Basalt FRP Reinforced Concrete Beams

This study involved conducting four-point bending tests on three types of rebar-reinforced concrete beam: those reinforced with steel bars, those reinforced using basalt fiber-reinforced polymer rods, and hybrid reinforced concrete beams that used both Basalt fiber-reinforced plastic and reinforcing steel. Various reinforcement ratios and configurations were used to analyze mid-span deflection, flexural capacity, fracture distribution, and Basalt FRP bars strain. The results suggest that using a hybrid reinforcement system that combines Basalt fiber-reinforced plastic and reinforcing steel can improve the transverse rupture strength of rebar-reinforced concrete beam, reduce deflection and cracking, and use the high-strength characteristics of Basalt FRP bars.

Form-finding of elastic gridshell based on spatial elastica model

In engineering design, elastic gridshells, which are composed of a number of elastic rods, are advantageous because they are lightweight, easy to construct, and low-cost as well as have a long-span space. However, the form-finding of a gridshell is challenging owing to the large deformation and strong geometric-nonlinearity of the structure.In this paper, a new form-finding method based on spatial elastica model (FMSE) is proposed. The deformations of elastic rods, obtained via the elliptic integral solution of spatial elastica, is integrated into the overall deformation of the gridshell. A set of transcendental equations is solved using the quasi-Newton method to ensure that the deformation of the gridshell satisfies the given boundary conditions. To validate the proposed FMSE method, desktop experiments (designed using the theory of Chebyshev nets) are performed on gridshells made of glass fiber reinforced polymer rods. The predictions of the FMSE method agree well with the experimental results.Accordingly, the proposed FMSE method is expected to have potential applications in elastic gridshells, on the investigations of form-finding, load-bearing capability, non-local deformation behavior, and also stability of structures.

Full-Range fatigue behavior of NSM CFRP-to-Concrete bonded joints

The interfacial bond characteristics and failure mechanism of near-surface mounted (NSM) fiber reinforced polymer (FRP) composites in concrete under fatigue loading are less understood compared to their bond behavior under static loading. In this paper, degradation of the local bond strength of FRP-to-concrete bonded joints subjected to direct pull-out fatigue loading is presented for both carbon FRP (CFRP) rods and strips under different fatigue load ranges, i.e., 10–50%, 10–60%, and 10–70%, of the corresponding static load-carrying capacity. The interfacial debonding between FRP and adhesive was observed during fatigue cycles for CFRP rod specimens to different extents. Specimens using CFRP rods with sand-coated and spirally wound surface treatment presented a higher local bond strength and a slower degradation rate, as compared to the ones using CFRP rods with roughened or sand-coated treatment. Using epoxy adhesives with higher strengths benefitted the fatigue bond performance of the tested specimens in terms of local bond strength and stable behavior. Higher fatigue load ranges substantially accelerated the local bond degradation resulting in a much shorter fatigue life of the bonded joints.

Hydrothermal aging of carbon fiber reinforced polymer rods intended for cable applications in civil engineering

Carbon fiber reinforced polymer (CFRP) composites have become increasingly popular due to their high strength-to-weight ratio and excellent mechanical properties. However, CFRP composites are susceptible to hydrothermal aging when used as cable applications in civil engineering, which can cause irreversible damage to their service performance. In this study, the effects of water immersion (water@60 °C), constant temperature and humidity exposure (95%RH@60 °C), and alternating hydrothermal environment (12h_60 °C&12h_25 °C@95%RH) were investigated on the property degradation of the CFRP rods. In addition, the water absorption behavior, and thermal and mechanical properties of the CFRP rods were systematically analyzed and compared. We found that elevated temperature and humidity accelerated the water absorption process, resulting in to the higher equilibrium moisture content and diffusion coefficient. Hydrothermal exposure led to maximum degradation in the tensile strength, three-point bending strength and short-beam shear strength of CFRP rods, with values reaching 4.8%, 17.4% and 24.3% in the water@60 °C, 95%RH@60 °C, and 12h_60 °C&12h_25 °C@95%RH conditions, respectively. Among the three mechanical performance properties analyzed, the tensile strength degradation of the CFRP rods was least affected by the three environmental conditions, primarily due to the tensile direction along the carbon fibers. In addition, the three-point bending and short-beam shear strength values of the CFRP rods showed the greatest degradation in the 12h_60 °C&12h_25 °C@95%RH environment. The long-term effects of the water molecules against the CFRP rods in the hydrothermal environment caused resin hydrolysis and debonding of the fiber-matrix interface, leading to degradation in three-point bending and short-beam shear strength. Additionally, the temperature alternating factor accelerated the degradation of the mechanical properties of the CFRP rods, and the mechanical properties of the CFRP rods declined most noticeably with alternating temperatures under the same moisture content conditions.

Mechanical behavior of glued-in GFRP rod in glubam: Experimental and analytical study

Fiber reinforced polymer (FRP) rod is a reasonable alternative to steel rod used in glued-in rod engineered bamboo structures, mainly attributed to its significantly higher strength-weight ratio and excellent corrosion resistance, while this field of study is almost empty. To fill this research gap, a total of 95 glued laminated bamboo (glubam) joints with single glued-in glass FRP (GFRP) rod were tested in a pull-pull tension loading program, aiming to shed light on the influence of anchorage length, rod diameter, bonding length-diameter ratio, glue-line thickness and rod-to-grain angle on the mechanical behavior. Particular emphasis was placed on the initial stiffness analysis and the explanation of the bond-slip mechanism based on the strain distribution of GFRP rod. Approximately 30% and 65% of the glued-in glubam joints can be categorized as the pure bonding failure at the glubam-adhesive interface and the shear failure in the glubam, respectively. It is found that the shear strength and initial stiffness of glubam joint decrease with increasing of the bonding length, the bonding length-diameter ratio, and the glue-line thickness, but the two indexes increase with increasing of GFRP rod diameter. The shear strength and initial stiffness exhibit an initial upward and then downward trend when the rod-to-main fiber direction angle varied from 0° to 90°. The analysis results reveal that the distribution of the local slip stiffness is non-uniform along the bonding length, also meaning that the local bond-slip relationships are varied at different locations. Based on the single-parameter correlation analysis, a strength model and an initial stiffness model are proposed for predicting the mechanical performance of glubam joints with glued-in GFRP rod for a potential application in evaluating actual glubam joints.

Finite Element Analysis of Flexural Strengthening of Reinforced Concrete Beams Using Near-Surface Mounted CFRP Rebars

Most of the standing structures today have already deteriorated or are on the verge of deterioration due to an increase in their age and harsh environmental conditions. For this very reason, the structures are in need of being upgraded or replaced. Retrofitting using near-surface mounted (NSM) fiber-reinforced polymer (FRP) rods has now emerged as a promising technique for strengthening the reinforced concrete members by increasing their flexural strength. This study aims to numerically investigate the efficiency of the NSM technique for flexural strengthening of RC beams by using finite element (FE) software, ABAQUS, and also evaluate the impact of variables such as concrete strength, embedded length of FRP rods, filler material used for the FRP rods, and the number of FRP rods provided. Validation of the finite element model was confirmed by first making a comparison with the experimental study presented in the literature for an un-strengthened beam. Thereafter, the validated model was used to simulate reinforced concrete beams strengthened with the NSM technique. The numerical results of the cracking moment, steel yielding moment, ultimate bending moment, and deflection at failure were reported and the impact of the variables was evaluated. The FE analysis results indicated that for the RC beams strengthened with NSM FRP rods, the flexural capacity significantly increased compared to the control beam, while the mid-span deflections of strengthened beams at failure decreased compared to the control beam.

Design of concrete beam reinforced with GFRP bars as per ACI codal provisions

This document provides design principles for concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars per the ACI 440.1R-15 regulation. One of the main advantages of using glass fiber reinforced polymer rods instead of traditional steel reinforced rods is their lighter weight and higher corrosion resistance. However, the bending failure mode of FRP reinforced concrete (FRP-RC) beams is brittle rather than ductile because the elasticity of fiber reinforced polymer (FRP) bars is linear until failure and the elongation at break is small. For FRP-RC elements, concrete crushing compression failure, which gives various warnings before failure, is the preferred failure mode. In other words, unlike the usual design practice for reinforced concrete (steel-RC) beams, for FRP-RC beams, an over-reinforced structure is preferable to an under-reinforced structure. In addition, since the FRP RC member has low rigidity of the FRP rod, it bends more and cracks larger than the steel RC member. These factors limit the field of application of FRP. Here is a design example of a rectangular beam with tension reinforcement according to ACI regulations.

Behavior of FRP rods under uniaxial tensile strength with multiple materials as an alternative to steel rebar

Steel corrosion raises maintenance costs and reduces the durability of steel-reinforced concrete structures. Therefore, societies must create their own sustainable model based on finding new technologies that enable them to benefit from the available resources thus reducing their construction cost and maintenance burdens. Fiber Reinforced Polymer (FRP) introduces an innovative and alternative approach to replace traditional steel bars and strands. So, this paper investigates the behavior of synthetic and natural FRP of different fiber volume fractions (Vf) under uniaxial tensile load. To carry out this, four types of fiber are made by hand lay-up technique. Three of them are synthetic fibers which include glass fibers, nylon fibers, and polypropylene fibers, whereas jute is used as natural fibers. The results show hand lay-up technique of FRP gives resembles the results of the Pultrusion process. The tensile strength and the elasticity modulus increased by increasing the Vf, regardless of the type of fiber. The samples GFRP-3, PFRP-P2, NFRP-N2, and JFRP-J3 showed the highest tensile strength of 971.89 MPa, 130.74 MPa, 262.54 MPa, and 178.42 MPa respectively, that improve by 26.68 %, 19.57 %, 15.44 %, 26.55 %, while the modulus of elasticity showed improvement by 20.13 %, 42 %, 14 %, and 32.93 % compared with a reference sample of the same group respectively. Furthermore, Microscope images indicated good fiber distribution and resin-fiber impregnation across the FRP bars.

Development of a new anchorage system for carbon fiber–reinforced polymer rods using extrusion process

Carbon fiber–reinforced polymer (CFRP) rods have been considered as a candidate material for prestressed concrete applications because of their superior properties. For current applications, successful use of CFRP rods is linked to an efficient anchorage system design. This paper presents a newly developed anchorage system for CFRP rods and the design concept that the extrusion process is used to generate gripping force. The proposed anchorage system consists of a steel barrel and an aluminum sleeve, and an extrusion region is designed on the outside of barrel to generate a suitable contact pressure distribution on the CFRP rod. A mathematical model was proposed to estimate the contact pressure on the CFRP rod and the capacity of anchorage system. The simulation of extrusion and loading process was conducted with a three-dimensional (3D) finite-element (FE) model. The key design parameters of anchorage system were analyzed to obtain an optimized parameter combination. The experimental validation showed that the new anchorage system is capable of allowing the CFRP rod to attain the ultimate tensile strength.

Predicting failure modes and load-capacity of fiber-reinforced polymer rods in adhesively bonded anchorages based on numerical modeling

The tensile properties of fiber-reinforced polymer (FRP) rods in adhesively bonded anchorages are expected to be studied in detail. Therefore, the study aims to predict the failure modes and load-bearing capacity (load-capacity) of FRP rods subjected to direct tensile force. The cohesive zone models were employed to evaluate the interfacial bond between materials. Firstly, two representative volume element models of fibers and matrix were proposed to predict engineering constants and strengths of the FRP material in three dimensions. Then, the main simulation, including the FRP rod, filling material, and steel tube, was carried out to analyze FRP rods under the variation of cohesive zone model parameters. The load-capacity, failure modes, shear-lag effect were predicted based on the maximum stress criterion. The results revealed that the FRP material strengths enforce the failure in two modes associated with the transverse and longitudinal directions of FRP rods. In addition, diameter is a significant factor that increases the shear-lag effect and reduces the tensile strength of the FRP rods. The numerical simulation provided a new method to predict the load-capacity of FRP rods.

Strengthening of building structures of historical masonry buildings in Syria with carbon fiber reinforced polymer (CFRP) rods and stainless steel helical rods

The article presents the most innovative methods of strengthening and (or) seismic strengthening of masonry for use in historical buildings that are of architectural value, for example, in old mosques in Syria, which are architectural monuments. These methods are designed to protect such buildings, many of which are of architectural and cultural value and are on the UNESCO World Heritage List, from cracks of various sizes and directions and from the negative effects of earthquakes that can occur at any time. Carbon fiber reinforced polymer rods (CFRP) rods and stainless steel helical rods are considered. Two mosques in Syria are briefly described as examples of historical masonry buildings, which are architectural monuments and objects of cultural heritage. In the end conclusions are drawn.

Numerical investigation on RC T-beams strengthened in the negative moment region using NSM FRP rods at various depth of embedment

The application of Near Surface Mounted (NSM) method to strengthen reinforced concrete (RC) members in flexure through the use of Fiber Reinforced Polymer (FRP) rods has become a subject of interest to designers and researchers over the past few years. This technique has been extensively applied, and there is still a need for more experiments, analytical, and numerical studies to determine the effects of their parameters on the flexural performance of RC members. Therefore, a detailed 3D nonlinear finite element (FE) numerical model was developed in this study to predict the load-carrying capacity and the response of RC T-beams strengthened in the negative moment region accurately through the use of NSM FRP rods at different depth of embedment which are placed under three-point bending loading. The model was, however, designed with due consideration for the nonlinear constitutive material properties of concrete, yielding of steel reinforcement, NSM rods, and cohesive behaviors to simulate the contact between two neighboring materials. Moreover, the findings of the numerical simulations were compared with those from the experiments by other investigators which involve two specimens strengthened with NSM FRP rods added to one unstrengthened control specimen. The results, however, showed that the mid-span deflection responses of the predicted FE were in line with the corresponding data from the experiment for all the flexural loading stages. This was followed by the use of the validated FE models to analyze the effect of several properties of the FRP materials to provide more information than the limited experimental data available. It was discovered that the FE model developed is appropriate to be applied practically and economically with more focus on the parametric studies based on design to precisely model and analyze flexural negative moment strengthening for the RC members through the use of NSM FRP rods.

ASSESSING SHEAR-LAG EFFECT ON PULTRUDED FRP RODS BASED ON A NUMERICAL SIMULATION

Fiber reinforced polymer rods fabricated from unidirectional fibers and a polymer matrix strengthen effectively reinforced concrete structures, such as the use in near-surface mounted systems. This study focused on aramid fiber reinforced polymer (AFRP) and analytically assessed the shear-lag effect that significantly affects the tensile capacity of the rod. A representative volume element model was employed for predicting the transversely isotropic properties of AFRP rods. In addition, a finite element simulation for the tension test model was performed to assess the shear-lag effect of an AFRP rod with various diameters. The study proposed a procedure for calculating the stress distribution in any cross-section of a fiber reinforced polymer rod. The simulation results agreed well with the previous experimental study. The findings clearly indicated the position of the failure section and the unequal tensile stress distribution in it. The study revealed that the shear-lag effect varied by the rod diameter affects the stress distribution at the failure section and the tensile capacity. The paper shows that the ultimate tensile capacity of any pultruded FRP rod can be predicted by the proposed method.

Negative moment region flexural strengthening system of RC T-beams with half-embedded NSM FRP rods: a parametric analytical approach

ABSTRACT Fiber Reinforced Polymer (FRP) rods are considered to be the most effective in retrofitting to increase the strength of reinforced concrete (RC) structures through Near-Surface Mounted (NSM) technique. There are, however, frequent cases encountered by engineers where the embedment depth mandated by ACI 440.2 R-08 code is not achievable in the field implementation. It has also been discovered that it is more challenging to strengthen the negative moment region of concrete members in comparison with the positive region. This research was conducted to determine the behavior of RC T-beams strengthened in the negative moment region using half-embedded NSM FRP rods. The findings were associated with the Modified Compression Field Theory (MCFT) which was applied in the analytical models. The model proposed was validated through a comparison with previous experimental study that showed half-embedded NSM FRP was effective as another method in comparison with the conventional soffit strengthening systems in retrofitting RC T-beams in the negative moment region, and good agreement was obtained. After that, a parametric analysis was initiated to determine the influence of FRP rod diameters, the compressive strength of concretes, the ratio of steel reinforcement as well as the materials used for the FRP on the flexural behavior of strengthened beams.

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.