Model For FRP-confined Concrete Research Articles

Compressive behavior of concrete jacketed in basalt TRM shell: Experiments and predictions

Compressive behavior of concrete jacketed in basalt TRM shell: Experiments and predictions

Experimental and model evaluation of cyclic compressive performance for RAC-filled BFRP tube composite columns

Experimental and model evaluation of cyclic compressive performance for RAC-filled BFRP tube composite columns

Reliability analysis of various modeling techniques for the prediction of axial strain of FRP-confined concrete

PurposeThe external confinement provided by the fiber-reinforced polymer (FRP) sheets leads to an improvement in the axial compressive strength (CS) and strain of reinforced concrete structural members. Many studies have proposed analytical models to predict the axial CS of concrete structural members, but the predictions for the axial compressive strain still need more investigation because the previous strain models are not accurate enough. Moreover, the previous strain models were proposed using small and noisy databases using simple modeling techniques. Therefore, a rigorous approach is needed to propose a more accurate strain model and compare its predictions with the previous models.Design/methodology/approachThe present work has endeavored to propose strain models for FRP-confined concrete members using three different techniques: analytical modeling, artificial neural network (ANN) modeling and finite element analysis (FEA) modeling based on a large database consisting of 570 sample points.FindingsThe assessment of the previous models using some statistical parameters revealed that the estimates of the newly recommended models were more accurate than the previous models. The estimates of the new models were validated using the experimental outcomes of compressive members confined with carbon-fiber-reinforced polymer (CFRP) wraps. The nonlinear FEA of the tested samples was performed using ABAQUS, and its estimates were equated with the calculations of the analytical and ANN models. The relative investigation of the estimates solidly substantiates the accuracy and applicability of the recommended analytical, ANN and FEA models for predicting the axial strain of CFRP-confined concrete compression members.Originality/valueThe research introduces innovative methods for understanding FRP confinement in concrete, presenting new models to estimate axial compressive strains. Utilizing a database of 570 experimental samples, the study employs ANNs and regression analysis to develop these models. Existing models for FRP-confined concrete's axial strains are also assessed using this database. Validation involves testing 18 cylindrical specimens confined with CFRP wraps and FE simulations using a concrete-damaged plastic (CDP) model. A comprehensive comparative analysis compares experimental results with estimates from ANNs, analytical and finite element models (FEMs), offering valuable insights and predictive tools for FRP confinement in concrete.

Load path dependence for passively and actively confined high-strength concrete

Load path dependence for passively and actively confined high-strength concrete

Confinement mechanism and modeling of basalt TRM confined concrete: Effect of mortar matrix grade

Confinement mechanism and modeling of basalt TRM confined concrete: Effect of mortar matrix grade

Ultimate Conditions Prediction and Stress–Strain Model for FRP-Confined Concrete Using Machine Learning

Ultimate Conditions Prediction and Stress–Strain Model for FRP-Confined Concrete Using Machine Learning

Transfer learning-based confinement strength prediction of concrete confined by FRP transverse reinforcements

Transfer learning-based confinement strength prediction of concrete confined by FRP transverse reinforcements

FRP spiral strip-confined concrete columns: Stress-strain behavior and size effect

FRP spiral strip-confined concrete columns: Stress-strain behavior and size effect

Axial stress–strain behaviour of bamboo composite tube-confined recycled aggregate concrete with different aggregate replacement ratios

ABSTRACT As an eco-friendly material, recycled aggregate concrete (RAC) has lower strength than natural aggregate concrete. To improve the compressive behaviour of RAC, a bamboo composite tube (BCT) is selected as the confining jacket. A total of 60 specimens were tested, which included 45 bamboo composite tube-confined recycled aggregate concrete (BTRAC) specimens and 15 unconfined RAC specimens. To investigate the influence of the replacement ratio of the recycled aggregate and thickness of BCT, a series of analysis were conducted on the failure modes, stress–strain response, dilation behaviour and effect of the replacement ratio. Test results showed that the axial stress–strain curves of the BTRAC specimens were approximately bilinear. The confinement ratio was found as the primary factor affecting the mechanical properties of the BTRAC column. Owing to a greater confinement stiffness in a thicker BCT, the slope of the second stage in the stress–strain curves increased correspondingly. Although the change in replacement ratio of recycle aggregate resulted in different dilation behaviours, the influence was regarded as limited on the BCT confinement effectiveness. Moreover, the ultimate stress, the ultimate strain, and the axial stress–axial strain curves of BTRAC specimens were calculated by the relevant models for FRP-confined concrete to evaluate their applicability.

Compressive Behavior of Concrete-Filled Filament-Wound FRP Tubes with Local Tube Damage

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are an emerging and attractive form of column for new constructions. Such a column consists of outer filament-wound FRP tubes that are filled with plain or steel-reinforced concrete. The fibers in the filament-wound FRP tube are predominantly in the hoop direction to confine the inner concrete, which leads to significantly enhanced strength and ductility in the confined concrete. Extensive studies have been conducted on the behavior of CFFTs that were subjected to various loading conditions, which confirmed the excellent performance of such members. As CFFTs become increasingly used in practice, there is a concern about the performance of CFFTs when the FRP tube is subjected to local damage that is caused by accidents, vandalism, or designed holes or cuts to accommodate connections with other structural components. Some studies have been carried out on the performance of CFFTs as flexural members with a locally damaged filament-wound FRP tube; however, the research on such CFFTs as columns remains limited. This paper presented the results of a comprehensive experimental program on the axial compressive behavior of CFFTs with a filament-wound FRP tube that was subjected to local tube damage. Two types of damage (i.e., holes and cuts) with different parameters were investigated. The test results showed that the compressive strength [i.e., peak stress (fcc′)] and the corresponding axial strain (ɛcc) of the damaged CFFTs were significantly reduced due to the local tube damage (e.g., fcc′ reduced from 12.2% to 64.8% and the corresponding ɛcc reduced from 35.2% to 77.2%). Finally, an existing model for FRP-confined concrete that considered the local FRP damage was evaluated which suggested the need for the recalibration of the model or the development of a new model for CFFTs with a locally damaged filament-wound FRP tube.

Cyclically loaded elliptical FRP-confined concrete: Behavioral characteristics and modeling

Cyclically loaded elliptical FRP-confined concrete: Behavioral characteristics and modeling

Hybrid FRP-concrete-steel double-skin tubular columns of varying slenderness ratios under eccentric compression

Hybrid FRP-concrete-steel double-skin tubular columns of varying slenderness ratios under eccentric compression

Behavior of large-scale hybrid FRP-concrete-steel double-skin tubular columns subjected to eccentric compression

Behavior of large-scale hybrid FRP-concrete-steel double-skin tubular columns subjected to eccentric compression

Stress-strain behavior of ECC-GFRP spiral confined concrete cylinders

This paper introduces a new confinement system that combines engineered cementitious composites (ECC) with glass fiber-reinforced polymer (GFRP) spiral as a protective cover to confine the concrete core. Meanwhile, the precast ECC-GFRP spiral cover also can serve as permanent formwork to improve construction efficiency and save construction costs. This study analyzed the confinement mechanism from the combination of ECC and GFRP spiral, and the effects of concrete strength and confinement stiffness on the stress-strain behavior of the confined concrete were investigated. The stress-strain behavior analyses confirm that the residual confining stress from ECC could enhance the ductility of the composite cylinder after GFRP rupture. Test results also indicate that an ECC-GFRP spiral layer has excellent crack control capability before peak loads, guaranteeing concrete cylinder durability. In addition, the model evaluation indicates that ultimate condition models for FRP-confined concrete are also applicable to ECC-GFRP spiral-confined concrete as long as the confining pressure from both ECC and GFRP spiral can be accurately predicted. A modified stress-strain model is proposed for this confinement form and performs well against test stress-strain curves.

Compressive behaviour of elliptical FRP tube-confined concrete columns

• A systematic experimental study on the compressive behaviour of elliptical FRP tube-confined concrete columns (EFCCCs) is presented. • The effects of the main column parameters, including the concrete strength, the thickness and fibre orientations of the FRP tube, and the aspect ratio of the cross-section, are clarified. • A new stiffness-based stress-strain model for the concrete in EFCCCs is proposed and shown to provide more accurate predictions than existing models. Elliptical FRP tube-confined concrete columns (EFCCCs) are an extension of circular FRP tube-confined concrete columns recently proposed at The Hong Kong Polytechnic University. Like their circular counterparts, EFCCCs are corrosion-resistant and can be used in situations where a column is subjected to substantially different loads in the two orthogonal lateral directions. The elliptical section of EFCCCs leads to more effective confinement of the concrete and an easier filament-winding fabrication process for the FRP tube compared with their rectangular counterparts. Existing studies on FRP-confined concrete in elliptical columns have been few. This paper first presents a systematic experimental study on the axial compressive behaviour of EFCCCs, with a focus on the stress-strain behaviour of the confined concrete. The test variables included the concrete strength, the thickness and fibre orientations of the FRP tube, and the aspect ratio of the cross-section. The test results showed that the confinement effectiveness of FRP tubes decreases with the aspect ratio and the concrete strength but increases with the FRP tube thickness. The orientations of fibres in the FRP tube were found to have a significant effect on its confinement effectiveness and the failure mode of EFCCCs. On the basis of the test results, existing stress-strain models for FRP-confined concrete in elliptical columns are evaluated. Furthermore, a new stress-strain model for the concrete in EFCCCs is proposed, which includes a more rigorous treatment of the confinement stiffness of EFCCCs and can provide more accurate predictions for the whole stress-strain curve than the existing models.

Analysis-oriented model for FRP tube-confined concrete: 3D interpretation of biaxial tube behaviour

Filament-wound fibre-reinforced polymer (FRP) tubes are an emerging FRP product employed in various FRP-concrete composite structures, such as concrete-filled FRP tubes (CFFTs). Due to the fibre orientations in the tube wall, the filament-wound FRP tube exhibits biaxial behaviour under simultaneous axial compression and hoop expansion, causing relaxation of the confining stress. Therefore, the conventional hoop tension test may result in overestimation of the confining stiffness. In this paper, the biaxial behaviour of FRP tubes is theoretically investigated using classical laminate theory in conjunction with an analysis-oriented model for FRP-confined concrete. The geometrical meaning of the biaxial tube behaviour is interpreted intuitively using the 3D geometrical approach previously proposed by the authors. For the convenience of analysis and design, this paper proposes a simplified approach to rectify the confining stiffness that considers both elastic and nonlinear biaxial effects. The predicted results show good agreement with the collected test data.

Probabilistic Calibration of Compressive Stress–Strain Models for FRP-Confined Concrete in Square Cross Section Members

The confinement effect of concrete by fiber-reinforced polymer (FRP) jackets may significantly enhance the axial compressive performance of concrete, although the results are variable. Therefore, rational calibration of deterministic models for compressive strength and the associated strain and stress–strain (SS) curves is required based on available experimental databases and selected probabilistic models. To improve the accuracy of the probabilistic model, second branch classifications for the stress–strain curve of FRP-confined concrete are identified within a series combination of uncertainties with computerized classification algorithms before probabilistic calibrations. The Bayesian theorem and Markov chain Monte Carlo (MCMC) approaches were used to update a probabilistic model that includes the critical variables that have been established in previous research. Furthermore, eight representative deterministic strength enhancement models, three strain enhancement models, and four stress–strain models were chosen for evaluation using credible intervals (CIs) and confidence levels (CLs) at different strain levels. Different types of FRPs were also analyzed individually to ensure the validity and reliability of the findings. The suggested probabilistic models can predict the properties of ultimate axial stress and related strain, thus offering an effective method for calibrating the confidence level and computational correctness of deterministic models previously published in the literature.

A versatile continuous model for predicting various post-peak patterns of FRP-confined concrete

• A continuous and integrable model is capable of describing all the post-peak patterns associated with diverse types of FRPs confined concrete. • The most comprehensive database to date, covering all categories of post-peak behaviours and types of FRPs. • The values of a strain efficiency factor for different types of FRPs have been determined. • The performance of some existing strength and strain models is evaluated. The utilization of fiber reinforced polymers (FRPs) is currently recognized as an effective solution against concrete deterioration. The external FRP not only provides strength and durability to the concrete structure but also propels the improvement of the internal concrete performance due to the confinement effect. To accurately predict the true response of the concrete core represented in various patterns caused by the confinement effect, a versatile continuous model is inevitable for analyzing the mechanical performance of confined concrete. To achieve this, in the present study, a comprehensive database has been established and reviewed. The confinement mechanisms and four post-peak patterns in terms of stress–strain relationship to the intensification of confinement effect are summarized. The ultimate state predictions and the mathematical expressions of stress–strain models are evaluated. Accordingly, the strain efficiency factors of different types of FRPs, and the methodology for four major coefficient parameters have been proposed to develop a versatile continuous model for FRP-confined concrete. Notably, the proposed model is a derivable, and integrable single-segment expression, which is capable of describing all the post-peak patterns associated with different types of FRPs.

Fiber-Reinforced Polymer-Confined Non-Circular Columns with Shape Modification: A Comprehensive Review.

The implementation of shape modification (SM) to reinforced concrete (RC) columns has been demonstrated to be effective when enhancing the effectiveness of the fiber-reinforced polymer (FRP) confinement of the columns, particularly for non-circular columns. The SM approach generally includes modifying a square section into a circular one, modifying a rectangular section into an elliptical/oval one and modifying a square/rectangular section into a curvilinearized square/rectangular section. In this paper, a state-of-the-art review of studies on FRP-confined non-circular columns with SM is conducted. The effects of key parameters on the effectiveness of FRP confinement are discussed, and different methods for the implementation of SM in real applications are briefly introduced. The findings of the review further confirm the effectiveness of the SM approach, and the test results demonstrate the effectiveness and advantages of section curvilinearization with a limited increase in cross-sectional area. Additionally, existing theoretical models for FRP-confined concrete in columns with SM are summarized. Further research opportunities associated with FRP-confined non-circular columns with SM are identified.

Behavior and design-oriented model for elliptical FRP-confined concrete under axial compression

• Elliptical FRP-confined high-strength concrete stub columns are axially loaded. • Increasing aspect ratio always has adverse effect on behavior of inner concrete. • Typical stress–strain curves of confined concrete are categorized into four types. • Threshold for sufficient confinement of elliptical FRP-confined concrete is given. • A design-oriented model for elliptical FRP-confined concrete is developed. Elliptical fiber-reinforced polymer (FRP)-confined concrete members have gained increasing attention due to their aesthetical characteristics and structural efficiency. This paper investigated the behavior of 24 elliptical FRP-confined concrete stub columns under axial compression. Effects of the amount of FRP confinement, the cross-sectional aspect ratio, and the use of high-strength concrete were discussed. The test results indicated that the stress and strain capacities of the confined concrete were enhanced with the increasing amount of FRP confinement. By contrast, the increasing sectional aspect ratio and the use of high-strength concrete had an adverse effect on the inner concrete’s axial behavior due to the increasingly non-uniform distribution of FRP confining pressure. In general, the typical stress–strain curves of elliptical FRP-confined concrete were categorized into four types. Furthermore, using the concept of equivalent diameter, the threshold for sufficient confinement of elliptical FRP-confined concrete was determined by the equivalent confinement stiffness ratio to ensure an overall ascending behavior. After addressing some key issues, a design-oriented model for elliptical FRP-confined concrete with a relatively wider range of concrete strength (from 32.6 to 72.4 MPa) was developed herein with more satisfactory accuracy than existing models. This model with a simple form could be naturally reduced to a widely accepted model for FRP-confined concrete with circular sections.