Strain Of FRP-confined Concrete Research Articles

Simulation of the ultimate conditions of fibre-reinforced polymer confined concrete using hybrid intelligence models

Fibre Reinforced Polymer (FRP) composites can provide efficient enhancements in terms of strength and deformability for concrete structures, in which accurate predictions of FRP confined concrete ultimate conditions is highly essential to maintain safety levels, further structural analysis and members design. In this paper, three novel hybrid intelligence models were proposed based on the hybridization of Support Vector Regression (SVR) model with three bio-inspired optimization algorithms as genetic algorithm (GA), particle swarm optimization (PSO) and Whale optimization algorithm (WOA) for predicting the ultimate conditions of FRP-confined concrete. Moreover, 15 existing empirical relations for the prediction of the ultimate strength and strain of FRP-confined concrete have been comprehensively reviewed. The performances of the empirical models and the proposed hybrid models as SVR-GA, SVR-PSO and SVR-WOA are evaluated and compared based on a large database, including 780 circular FRP-confined concrete specimens, which are collected from the open-source published experiments. By comparing the predicted results based on several statistical indicators, the proposed hybrid SVR-models are generally outperforming the existing empirical relations in terms of accuracy and agreement with the experimental database. SVR-WOA provides superior performances than SVR-PSO, SVR-GA and all existed empirical models. The root mean square error is improved using SVR-WOA by 0.9%, 14.9 % and 37% for the ultimate strain capacity, and 2.7%, 4.6% and 17.3% for the ultimate strength compared to SVR-PSO, SVR-GA and the best empirical relation, respectively.

Prediction of Properties of FRP-Confined Concrete Cylinders Based on Artificial Neural Networks

Recently, the use of fiber-reinforced polymers (FRP)-confinement has increased due to its various favorable effects on concrete structures, such as an increase in strength and ductility. Therefore, researchers have been attracted to exploring the behavior and efficiency of FRP-confinement for concrete structural elements further. The current study investigates improved strength and strain models for FRP confined concrete cylindrical elements. Two new physical methods are proposed for use on a large preliminary evaluated database of 708 specimens for strength and 572 specimens for strain from previous experiments. The first approach is employing artificial neural networks (ANNs), and the second is using the general regression analysis technique for both axial strength and strain of FRP-confined concrete. The accuracy of the newly proposed strain models is quite satisfactory in comparison with previous experimental results. Moreover, the predictions of the proposed ANN models are better than the predictions of previously proposed models based on various statistical indices, such as the correlation coefficient (R) and mean square error (MSE), and can be used to assess the members at the ultimate limit state.

Nonlinear modeling of ultimate strength and strain of FRP-confined concrete using chaos control method

It is now well known that the confinement of concrete with fiber-reinforced polymer (FRP) composites can increase its strength and deformability. This paper presents a general nonlinear regression model to predict the ultimate conditions of FRP-confined concrete based on an iterative chaos control method (CCM). A dynamic chaos control factor is also proposed using the logistic map and a self-adaptive step size to achieve stabilization of the iterative chaos control method. To this end, a large database of axial compression tests on 769 circular FRP-confined concrete specimens was compiled from the published literature. Using the iterative method and the database, three nonlinear design-oriented models are developed and one of them is proposed for design applications. The results of this study show that the chaos control method can be successfully applied in the development of nonlinear models to predict the ultimate strength and strain of FRP-confined concrete.

Modeling the behavior of FRP-confined concrete using dynamic harmony search algorithm

The accurate prediction of ultimate conditions for fiber reinforced polymer (FRP)-confined concrete is essential for the reliable structural analysis and design of resulting structural members. Nonlinear mathematical models can be used for accurate calibration of strength and strain enhancement ratios of FRP-confined concrete. In this paper, a new procedure is proposed to calibrate the nonlinear mathematical functions, which involved the use of a dynamic harmony search (DHS) algorithm. The harmony memory is dynamically adjusted based on a novel pitch generation scheme using a dynamic bandwidth and random number with normal standard distribution in DHS. A new design-oriented confinement model is proposed based on three influential factors of FRP area ratio ($$ \rho_{a} $$źa), lateral confinement stiffness ratio ($$ \rho_{E} $$źE), and strain ratio ($$ \rho_{\varepsilon } $$źź). Five nonlinear mathematical design-oriented models are regressed on approximately 1000 axial compression tests of FRP-confined concrete in circular sections based on the proposed DHS algorithm. The proposed models for the prediction of the ultimate axial stress and strain of FRP-confined concrete are compared with the existing models. It has been shown that the DHS algorithm offers the best performance in terms of both accuracy and fast convergence rate in comparison with the other modified versions of harmony search algorithms for optimization problems. The proposed design-oriented model provides improved accuracy over the existing models.

Probabilistic Design Models for Ultimate Strength and Strain of FRP-Confined Concrete

AbstractThis paper presents a probabilistic procedure for deriving design models for the ultimate strength and strain of fiber–reinforced-polymer (FRP)-confined concrete. First, a large database of axial compression tests performed on circular FRP-confined concrete specimens is collected for calibrating an ultimate strength model, based on the Drucker-Prager criterion, and an ultimate strain model, based on the ultimate dilation rate. The database is also employed for deriving a probabilistic model for the FRP strain efficiency factor. The calibrated models, though simple, show superior performance over some of the models in the literature. Then, using the Central Limit Theorem and considering uncertainty in the mechanical properties of the concrete and FRP material as well as their correlation, analytical probabilistic design models for the ultimate strength and strain of FRP-confined concrete are derived. These models can be used in the design and reliability analysis of FRP-confined columns.

Stress–strain behavior of actively and passively confined concrete under cyclic axial load

Monotonic stress–strain relationship of actively-confined concrete has been used as the base model to establish analysis-oriented stress–strain model of fiber reinforced polymer (FRP) confined concrete. This approach is based on the assumption that the axial stress and strain of FRP-confined concrete are the same as those of actively confined concrete under the same confinement pressure and lateral strain. In this study, an experiment was conducted to verify this assumption for concrete subjected to cyclic loading. A total of 31 actively confined and FRP-confined concrete cylinders were tested. The results indicate that this assumption is not applicable to concrete under cyclic loading; a gap was found between the envelop curves of the two types of confined concrete. In addition, the test results also reveal that confinement pressure significantly affects both reloading modulus and plastic strain which are the main factors controlling cyclic behavior of confined concrete.

Stress-Strain Model for Fiber-Reinforced Polymer-Confined Concrete

The design of fiber-reinforced polymer (FRP)-confined concrete members requires accurate evaluation of the performance enhancement due to the confinement provided by FRP composite jackets. A strain ductility-based model is developed for predicting the compressive behavior of normal strength concrete confined with FRP composite jackets. The model is applicable to both bonded and nonbonded FRP-confined concrete and can be separated into two components: a strain-softening component, which accounts for unrestrained internal crack propagation in the concrete core, and a strain-hardening component, which accounts for strength increase due to confinement provided by the FRP composite jacket. A variable strain ductility ratio described in a companion paper is used to develop the proposed stress-strain model. Equilibrium and strain compatibility are used to obtain the ultimate compressive strength and strain of FRP-confined concrete as a function of the confining stiffness and ultimate strain of the FRP jacket.