Fiber Reinforced Polymer Beams Research Articles

Prediction of flexural strength in FRP bar reinforced concrete beams through a machine learning approach

PurposeThe purpose of this study is to assess the incorporation of fiber reinforced polymer (FRP) bars in concrete as a reinforcement enhances the corrosion resistance in a concrete structure. However, FRP bars are not practically used due to a lack of standard codes. Various codes, including ACI-440-17 and CSA S806-12, have been established to provide guidelines for the incorporation of FRP bars in concrete as reinforcement. The application of these codes may result in over-reinforcement. Therefore, this research presents the use of a machine learning approach to predict the accurate flexural strength of the FRP beams with the use of 408 experimental results.Design/methodology/approachIn this research, the input parameters are the width of the beam, effective depth of the beam, concrete compressive strength, FRP bar elastic modulus and FRP bar tensile strength. Three machine learning algorithms, namely, gene expression programming, multi-expression programming and artificial neural networks, are developed. The accuracy of the developed models was judged by R2, root means squared and mean absolute error. Finally, the study conducts prismatic analysis by considering different parameters. including depth and percentage of bottom reinforcement.FindingsThe artificial neural networks model result is the most accurate prediction (99%), with the lowest root mean squared error (2.66) and lowest mean absolute error (1.38). In addition, the result of SHapley Additive exPlanation analysis depicts that the effective depth and percentage of bottom reinforcement are the most influential parameters of FRP bars reinforced concrete beam. Therefore, the findings recommend that special attention should be given to the effective depth and percentage of bottom reinforcement.Originality/valuePrevious studies revealed that the flexural strength of concrete beams reinforced with FRP bars is significantly influenced by factors such as beam width, effective depth, concrete compressive strength, FRP bars’ elastic modulus and FRP bar tensile strength. Therefore, a substantial database comprising 408 experimental results considered for these parameters was compiled, and a simple and reliable model was proposed. The model developed in this research was compared with traditional codes, and it can be noted that the model developed in this study is much more accurate than the traditional codes.

Vibration-based detection of non-overlapping delaminations in FRP beams using frequency shifts

Extensive research has been carried out on the detection of single delamination in fibre-reinforced polymer (FRP) structures using different structural health monitoring (SHM) approaches, including the vibration-based assessment methods. However, there are limited studies that on the detection of multiple delaminations, which could occur in many real-world scenarios. To address this research gap, this paper aims at developing a vibration-based method to assess the two non-overlapping delaminations in FRP beams based on changes in natural frequencies. A theoretical model of vibrating FRP beams with two non-overlapping delaminations was constructed and used for generating the multiple frequencies of the delaminated beams. By analysing the frequency shifts of the FRP beams before and after the occurrence of damage, the delamination characteristics (location and severity) can be inversely predicted using optimisation algorithms. The accuracy and efficiency of the frequency-based inverse algorithm were verified experimentally by modal testing on FRP beam specimens with one and two non-overlapping delaminations. It is interesting to observe that using the proposed vibration-based method, the single delamination in FRP specimens can also be predicted as two non-overlapping delaminations, with a major one matching the original single delamination and a minor one that can be neglected. Thus, the current vibration-based delamination assessment approach is flexible in identifying the prediction of either single or double non-overlapping delaminations in FRP beams, and therefore, it potentially has wider applicability than the existing single delamination detection methods.

Vibration-based prediction of residual fatigue life for composite laminates through frequency measurements

Fiber reinforced polymer (FRP) structures may experience cumulative fatigue damage during their service life which can lead to structural failure. This paper focuses on predicting the residual fatigue life of FRP structures using vibration parameters. The relationship between residual fatigue life and natural frequencies is examined through modal testing and fatigue measurements on FRP beam specimens. Two prediction methods; semi-empirical models and machine learning (ML) algorithms, are utilized. The semi-empirical models are derived from existing “residual stiffness” models based on the relationship between bending stiffness and flexural frequencies. ML algorithms Support Vector Machine (SVM) and Artificial Neural Network (ANN), are developed for fatigue life prediction. Experimental validation is performed using measured frequencies during fatigue testing of FRP beams. The ML algorithms can use multimode frequencies unlike single mode of semi-empirical models. The verification results show that the ML algorithms can be used to predict the residual fatigue life with the selection of the appropriate mode of frequency. The results show that ML algorithms outperform single-mode frequency inputs, and the use of higher modes of measured frequencies improves the precision of fatigue life prediction. An inverse algorithm based on SVM exhibits higher prediction accuracy and stability, even with limited training samples.

Changes in fracture energy at FRP-concrete interfaces following indoor and outdoor exposure with sustained loading

Small-scale plain concrete precracked beams strengthened with carbon and glass fiber reinforced polymer (FRP) sheets were tested in 3-point flexure to evaluate changes in the FRP-concrete Mode II interfacial fracture energy following sustained loading for 6 and 13 years in indoor and outdoor environments. Mode II fracture energy of the interfacial region, GF, was calculated using strain profiles along the length of the FRP sheet, which were measured using digital image correlation and photoelastic techniques. In the post-conditioned experiments, larger GF values were measured as the debonded zone progressed from the sustained shear stress transfer region to the unstressed portion of the interfacial region far from the notch, particularly in beams with outdoor conditioning. In the interfacial region near the notch, the carbon FRP beams showed no reduction in GF in the indoor environment but reduction in the outdoor environment, while glass FRP showed reductions in both environments. In outdoor beams with glass FRP sheets, GF was not additionally degraded when the FRP was exposed to direct sunlight, in comparison to beams with the FRP exposed to indirect sunlight.

Shear Strength Prediction of Concrete Beams Reinforced with FRP Bars and Stirrups Using Gene Expression Programming

Existing reinforced concrete (RC) structures in humid regions suffer from deterioration due to the corrosion of ordinary reinforcement bars damaging the whole system. The deterioration of the transverse reinforcement leads to shear failure, which is one of the most dangerous failure modes. Therefore, researchers suggested using fiber-reinforced polymer (FRP) bars as a replacement for reinforcement bars in humid regions to integrate sustainability and improve their serviceability and durability. A simple model that can accurately estimate the shear strength of concrete beams designed with FRP longitudinal bars and stirrups is lacking. This research proposed a simplified Gene expression programming (GEP) based model to estimate the shear strength of FRP concrete beams. Seven parameters that principally dominate the shear behavior of FRP beams were utilized to create the GEP model. The parameters are the beam width, beam depth, concrete compressive strength, FRP tensile longitudinal reinforcement ratio, area of stirrups, spacing between the stirrups, and the ultimate FRP strength of stirrups. A comparison was made between the GEP and ACI-440 models; the R2 values of the total database were 92% and 54% for the GEP and ACI models, respectively. The R2 of the GEP model is considerably higher than that measured for the ACI model, and the errors of the GEP model are low, which affirms that the GEP is superior to the ACI model in estimating the shear strength of FRP beams. The trends of the GEP and ACI-440 models and the empirical results are similar, confirming the GEP model’s consistency. Using the GEP model to estimate the shear strength of concrete beams designed with FRP longitudinal bars and stirrups is recommended.

Reinforced Concrete Beams Strengthened with Externally Bonded Hybrid FRP Sheets

Fiber Reinforced Polymer (FRP) is commonly used in structural repair and strengthening due to its high tensile strength, non-corrosive and lightweight. On the other side FRP is relatively brittle compared to steel. This study used hybrid FRP consisting of GFRP and CFRP, by combining two type of FRP with different characteristic it is to be expected that the more brittle FRP will fail first followed by the more elastic one, therefore creating a sequential failure. However CFRP have a higher tensile strength in comparison to GFRP, therefore it’s necessary to reduce its tensile strength by reducing its volume. This study is divided into two topics, hybrid FRP tensile strength test and beam flexural test. For the hybrid FRP tensile strength test, a total of three variation of hybrid FRP will be compared (GC30, GC40, and GC50). The variation that shown a sequential failure behaviour, will then be applied to a reinforced concrete beam and tested under monotonic point load device. The test result shown that sequential failure occur on GC30 and GC40. However GC40 had a higher ultimate load at 24.86 kN. For the beam flexural test, there will be two variation, i.e. control beam (CB) and beam strengthened with hybrid FRP (BGC). When compared, BGC had a 40.0% increase in yield strength and 55.43% increase for ultimate load.

Flexural Behavior of Reinforced Concrete Beams with FRP Bars Exposed to Elevated Temperature

The present study aims to evaluate the performance of concrete beams with different Fiber Reinforced Polymer (FRP) and steel bars exposed to elevated temperatures through a detailed experimental investigation. Flexural behavior of beams is analyzed with Carbon Fiber Reinforced Polymer bars (CFRP), Basalt Fiber Reinforced Polymer bars (BFRP), Glass Fiber Reinforced Polymer bars (GFRP), and steel bars tests. Beams were exposed to elevated temperature 925 °C (1 hr) following standard fire curve, and subsequently cooled by either natural or forced water spraying. After the cooling, beam specimens were tested under four-point loading up to the failure load. Ultimate load and deflection profile of heated and unheated beams are evaluated. At higher temperatures (925 °C), the steel and GFRP specimens show a higher strength loss of about 60–80% with higher deformation values. The load carrying capacity of CFRP beams is found to be higher as compared to other types of beams. Specimens cooled by water shows higher strength loss of about 7–12% than air cooled specimens. The failure pattern of beams with FRP and steel beams are different, and it is based on heating cooling regime.

The influence of delamination parameters on the wavelet based damage index in CFRP structures

This study performs a substantial statistical analysis on the effects of damage characteristics, such as position and severity, on a specific damage metric composed of coefficients obtained from the discrete wavelet transform. The results of the analysis serve as the basis for developing more sophisticated and optimized damage-identifying methods in structural health monitoring. For the methodological procedure, a carbon fiber reinforced polymer beam was numerically modeled using the finite element method where the damage was induced considering a local reduction of stiffness in different positions and levels of severity. The numerical methodology was validated with modal experimental tests. Results obtained through analysis of variance and design of experiments indicated the sensitivity of each factor and the response surface provided the best combination of factors for each response. Knowing the sensitivity and interaction of these parameters is essential for the correct formulation of damage indexes or other techniques in damage identification. The results obtained in this paper can be used as a guideline for engineers when developing new wavelet transform-based strategies for structural health monitoring.

A Review on Strengthening of Timber Beams Using Fiber Reinforced Polymers

Fiber reinforced polymer (FRP) has been used in the construction industry because of its advantages such as high strength, light weight, corrosion resistance, low density and high elasticity. This paper presents a review of bonding techniques adopted to strengthen timber beams using FRP to achieve larger spans. Different methods of bonding between FRP and timber beams have been summarized with a focus on the influencing factors and their effects as well as relevant bond-slip models proposed for fundamental understanding. Experimental investigations to evaluate the flexural performance of timber beams strengthened by FRP bars, sheets and wraps have also been critically reviewed to identify key influencing parameters. Limited research available on the shear performance of FRP reinforced timber beams have been analyzed to determine the influencing factors of the shear performance in timber-FRP beams. The paper finally presents an overall summary of the current-state-of-the-art and proposes some future research directions in the field.

Influence of graphene fillers on vibration characteristics of tapered hybrid GFRP composite beams under elevated temperature condition: Numerical and experimental study

In this study, numerically and experimentally the dynamic characteristics of graphene-reinforced glass fiber–reinforced polymer hybrid uniform and thickness tapered laminated composite beams were investigated. First, the graphene-epoxy nanocomposite solution without and with 0.25, 0.50, and 0.75 wt.% of graphene reinforcement is prepared by the heat shearing technique and then used for the fabrication of glass fiber–reinforced polymer hybrid uniform and thickness tapered composite beams using the hand lay-up method. The elastic properties of the hybrid beams were evaluated using the impulse excitation of vibration technique (ASTM E1876-15) under elevated temperature. Further, the numerical and experimental modal analysis of the hybrid beams with uniform and tapered configurations were conducted with variation in wt.% of graphene particles under fixed-fixed and fixed–free end supports. The results reveal that the natural frequencies of the glass fiber–reinforced polymer hybrid uniform and tapered configurations with 0.25 wt.% of graphene are greater than those of the glass fiber–reinforced polymer beams without graphene reinforcement and observed lesser for 0.5 and 0.75 wt.% of graphene under fixed-fixed and fixed-free end supports, respectively, due to unavoidable agglomeration effects. Furthermore, the parametric study was performed with the influence of weight fraction of graphene and temperature on the transverse response of the tapered composite beam. Hence, it can be concluded that the use of graphene filler in the glass fiber–reinforced polymer composites in the tapered composite beams improves the bending natural frequencies significantly when the weight fraction of the graphene is used lesser as agglomeration is unavoidable in practical condition. Therefore, the comprehensive numerical and experimental work presented in this study will be useful to the designers while using graphene fillers to improve the bending characteristics of the tapered composite beams.

Study on the anti-collision performance of basalt fiber reinforced polymer beam–column guardrail

In view of poor performance and short service life of conventional bridge guardrails against vehicle collision in practice, a continuous basalt fiber reinforced polymer (BFRP) guardrail was proposed. The quasi-static bending test of BFRP pipe was carried out and simulated by nonlinear explicit dynamics software LS-DYNA, and then the new guardrail was evaluated using LS-DYNA. Results revealed that the vehicles do not appear to cross, ride across, and pass through the guardrails, implying that the BFRP guardrail has a good guiding performance. The vertical and horizontal acceleration values at the seat position during the collision are all less than 200 m/s2 in the specification, indicating that the BFRP guardrail has a good cushioning function for the vehicle. Compared with the steel guardrails, the BFRP guardrail can better reduce the acceleration of the vehicle, and the energy absorption of the BFRP guardrail is higher than that of the steel guardrail. Therefore, the anti-collision performance of the BFRP guardrail is better than that of the steel guardrail.

Bayesian damage localization and identification based on a transient wave propagation model for composite beam structures

This paper proposes the use of a physics-based Bayesian framework for the localization and identification of damage in composite beam structures using ultrasonic guided-waves. The methodology relies on a transient wave propagation model based on wave and finite element scheme that efficiently provides time-domain signals that are compared with the ultrasonic measurements within a multilevel Bayesian framework. As a key contribution, the proposed methodology enables the localization and identification of damage using just the signals without any baseline comparison or further transformation, hence reducing additional sources of uncertainty. The proposed Bayesian approach allows (1) the localization of the defect, and (2) the identification of different candidate damage hypotheses and their ranking based on probabilities that measure their relative degree of belief. The methodology is illustrated in carbon fiber reinforced polymer beams with different layups. An investigation into how the measurement noise can impact the identified damage properties is also provided. The results show the effectiveness and efficiency of the proposed approach in reconstructing and identifying different types of damage in long and complex composite beams at a relatively low computational cost.

Experimental investigation on concrete beams reinforced with basalt fiber reinforced polymer bars

Abstract This paper dealt with the flexural behaviour study on reinforced concrete beams with conventional steel and basalt rebar using Portland Pozzolana Cement. Conventional steel bars are vulnerable to various environmental attacks and aggressive attacks such as corrosion. Basalt rebar can effectively overcome this problem due to the enhanced properties like inhibiting corrosion, high tensile strength, low young’s modulus, lightweight and resist electrical conductivity. In this paper, flexural behaviour of conventional Steel Reinforced Beam (SRB) and Basalt Fiber Reinforced Polymer beam (BFRB) were investigated experimentally and test results arrived were elaborately discussed. It has been noticed that BRB shows significant greater deflection when compared to SRB due to lower elastic modulus, whereas flexural load carrying capacity of BRB increases due to enriched tensile strength property in basalt rebar, significant increase of tensile strength in BRB. The results revealed that basalt rebar can be effectively used in construction as a replacement of conventional steel reinforcement for sustainable development.

Lateral-Torsional Buckling Strength of Two-Span Glass Fiber Reinforced Polymer Beams

This paper presents the outcome of a study of two-span glass fiber reinforced polymer (GFRP) I-section beams susceptible to lateral-torsional buckling when subjected to gradually increasing concentrated vertical load(s) in the presence of two different types of lateral bracing schemes. It is found that loading one span results in a smaller buckling load as compared with the cases with loading in both spans regardless of the type of bracing scheme used. Also, the study shows that the addition of midspan braces for the GFRP beams results in up to 5.5 times increase in the buckling load capacity.

Lateral-Torsional Buckling Strength of Two-Span Glass Fiber Reinforced Polymer Beams

This paper presents the outcome of a study of two-span glass fiber reinforced polymer (GFRP) I-section beams susceptible to lateral-torsional buckling when subjected to gradually increasing concentrated vertical load(s) in the presence of two different types of lateral bracing schemes. It is found that loading one span results in a smaller buckling load as compared with the cases with loading in both spans regardless of the type of bracing scheme used. Also, the study shows that the addition of midspan braces for the GFRP beams results in up to 5.5 times increase in the buckling load capacity.

A Numerical Method to Model Non-linear Damping Behaviour of Martensitic Shape Memory Alloys.

This article investigates the efficiency of hybridizing composites with thin layers of martensitic shape memory alloys for improvement of damping. The non-linear damping behaviour of martensitic shape memory alloys is simulated using a modified version of Masing’s rules. The model was implemented in a user subroutine of a finite element code, and validated by a numerical simulation of experimental hysteresis loops at different maximum strain amplitudes. The experimental free decay of hybridized glass fiber reinforced polymer beams was simulated using the finite element model, including the validated model of the investigated materials. The amplitude-dependent damping of the hybrid beams in free decay was reproduced successfully in the numerical analysis and it was proven that the hybridization technique is efficient for improvement of damping.

Bonded Sleeve Connections for Joining Tubular Glass Fiber–Reinforced Polymer Beams and Columns: Experimental and Numerical Studies

AbstractA bonded sleeve connection was developed for joining tubular glass fiber–reinforced polymer (GFRP) beams and columns. It utilizes a sleeve connector made by welding a steel tube to a steel ...

Vibration-based assessment of delaminations in FRP composite plates

Delamination is a frequently occurring type of damage in laminated fibre reinforced polymer (FRP) composites and causes substantial loss in structural stiffness and usable service life. The detection of delaminations in FRP composites is critical for the safe and reliable use of these materials in aeronautical and other industries. Structural Health Monitoring (SHM) techniques based on vibration measurements have proven to be promising towards this end. There have been comprehensive studies of FRP beams with through-width delaminations, but the damage assessment of FRP plates with embedded delaminations using frequency-based detection has not been extensively studied. To solve the inverse problem of determining size and location of delamination from changes in the natural frequencies, this paper presents a new surrogate assisted optimisation (SAO) method for predicting the location and size of delaminations in fibre reinforced composite plates using natural frequency shifts as indicative parameters. The proposed frequency-based delamination assessment method is validated using finite element models of FRP plates with embedded delaminations and by experimental modal analysis. Modal testing was conducted using scanning laser vibrometer on carbon/epoxy and glass/epoxy FRP plates that were manufactured with artificially induced delaminations. The proposed SAO algorithm was compared to an Artificial Neural Network (ANN) method in terms of database size, prediction accuracy and sensitivity to noisy data. The results show that the proposed inverse algorithm can predict the delamination parameters of location and size with good accuracy for numerically simulated frequency shift data but the prediction accuracy was reduced with experimental data. A comparison of the two inverse algorithms show that the SAO method has significant advantages compared to the ANN algorithm for delamination prediction.

Delamination Identification for FRP Composites with Emphasis on Frequency-Based Vibration Monitoring-A Review

Fibre reinforced polymer (FRP) composite laminates are now commonly used in many structural applications, especially in the aerospace industry, where margins of safety are kept low in order to minimise weight. Timely detection and assessment of damage (in particular delaminations) in composite laminates are therefore critical, as they can cause loss of structural integrity affecting the safe operation of the composite structures. The current trend is towards implementation of structural health monitoring (SHM) systems which can monitor the structures in situ without down time. In this paper, first, the current available SHM techniques for delamination detection in FRP composites are briefly reviewed, including acoustic emission, fibre optic sensors, Lamb wave-, impedance- and vibration-based methods. Among different vibration-based methods, frequency monitoring is the simplest to implement, requiring only single point measurement, and is relatively accurate and reliable, thus it becomes the main focus of present paper. A comprehensive review of frequency-based vibration monitoring is conducted in terms of the various aspects of delamination identification in FRPs through frequency shifts, including review of theoretical models for free vibration of delaminated FRP beams, survey of finite element modelling of delaminated composite structures, summary of experimental modal analyses on FRP composites with delaminations, and inverse algorithms for frequency-based delamination assessment. This paper aims to help the readers to get an overview of the available SHM techniques for monitoring the integrity of FRP composites, with a special emphasis on delamination assessment through frequency-based vibration monitoring.

An investigation of material characterization of pultruded FRP H- and I-beams

ABSTRACTThis study presents the material characterization of pultruded fiber-reinforced polymer beams of different sizes using experimental and analytical methods. Various tests were performed to determine the material properties such as Young's and shear moduli using tensile and bending tests of coupons and beams. The stiffness measured from the four-point bending test of both beams is in close agreement with analytical methods. It is shown that the numerically obtained flexural response of the beam using ABAQUS software with material properties obtained from the four-point beam bending test is close to the experimental response.