• Computers and Concrete
• /
• v.30 no.6
• /
• pp.377-391
• /
• 2022

The use of carbon fiber-reinforced polymers (CFRP) has widely increased due to its enhancement in the ultimate strength and ductility of the reinforced concrete (RC) structures. This study presents a prediction model for the axial compressive strength and strain of normal-strength concrete cylinders confined with CFRP. Besides, soft computing approaches have been extensively used to model in many areas of civil engineering applications. Therefore, the genetic expression programming (GEP) models to predict axial compressive strength and strain of CFRP-confined concrete specimens were used in this study. For this purpose, the parameters of 283 CFRP-confined concrete specimens collected from 38 experimental studies in the literature were taken into account as input variables to predict GEP based models. Then, the results of GEP models were statistically compared with those of models proposed by various researchers. The values of R² for strength and strain of CFRP-confined concrete were obtained as 0.897 and 0.713, respectively. The results of the comparison reveal that the proposed GEP-based models for CFRP-confined concrete have the best efficiency among the existing models and provide the best performance.

• Structural Engineering and Mechanics
• /
• v.26 no.2
• /
• pp.127-150
• /
• 2007

The objective of this paper is to develop a finite element procedure for predicting the compressive strength and ultimate axial strain of Carbon Fiber Reinforced Plastics (CFRP) confined circular concrete columns and to study the effective parameters of confinement efficiency for helping design of CFRP retrofit technology. The behavior of concrete confined with CFRP is studied using the nonlinear finite element method. In this paper, effects of column size, CFRP volumetric ratio and plain concrete strength are studied. The confined concrete nonlinear constitutive relation, concrete failure criterion and stiffness reduction methodology after concrete cracking or crushing are adopted. First, the finite element model is verified by comparing the numerical solutions of confined concrete with experimental results. Then the effects of column size, CFRP volumetric ratio and plain concrete strength on the peak strength and ductility of the confined concrete are considered. The results of parametric study indicate that the normalized column axial strength increases with increasing CFRP volumetric ratio, but without size effect for columns with the same CFRP volumetric ratio. As the same, the increase in column ductility depends on CFRP volumetric ratio but without size effect for columns with the same CFRP volumetric ratio.

• Computers and Concrete
• /
• v.8 no.5
• /
• pp.597-616
• /
• 2011

With respect to rehabilitation, strengthening and retrofitting of existing and deteriorated columns in buildings and bridges, CFRP sheets have been found effective in enhancing the performance of existing RC columns by wrapping and bonding CFRP sheets externally around the concrete. Concrete columns and piers that are confined by both lateral steel reinforcement and CFRP are sometimes referred to as "hybrid" concrete columns. With the availability of experimental data on concrete columns confined by steel reinforcement and/or CFRP, the study presents modeling using artificial neural networks (ANNs) to predict the compressive strength of hybrid circular RC columns. The prediction of the ultimate confined compressive strength of RC columns is very important especially when this value is used in estimating the capacity of structures. The present ANN model used as parameters for the confining materials the lateral steel ratio (${\rho}_s$) and the FRP volumetric ratio (${\rho}_{FRP}$). The model gave good predictions for three types of confined columns: (a) columns confined with steel reinforcement only, (b) CFRP confined columns, and (c) hybrid columns confined by both steel and CFRP. The model may be used for predicting the compressive strength of existing circular RC columns confined with steel only that will be strengthened or retrofitted using CFRP.

• Structural Engineering and Mechanics
• /
• v.18 no.2
• /
• pp.167-194
• /
• 2004

In this paper axial loading tests on low strength concrete members, which were confined with various thickness of carbon fiber reinforced polymer (CFRP) composite sheets are described. Totally 46 specimens with circular, square and rectangular cross-sections with unconfined concrete compressive strengths between 6 and 10 MPa were included in the test program. During the tests, a photogrammetrical deformation measurement technique was also used, as well as conventional measurement techniques. The contribution of external confinement with CFRP composite sheets to the compressive behavior of the specimens with low strength concrete is evaluated quantitatively, in terms of strength, longitudinal and lateral deformability and energy dissipation. The effects of width/depth ratios and the corner radius of the specimens with rectangular cross-section on the axial behavior were also examined. It was seen that the effectiveness of the external confinement with CFRP composite sheets is much more pronounced, when the unconfined concrete compressive strength is relatively lower. It was also found that the available analytical expressions proposed for normal or high strength concrete confined by CFRP sheets could not predict the strength and deformability of CFRP confined low strength concrete accurately. New expressions are proposed for the compressive strength and the ultimate axial strain of CFRP confined low strength concrete.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.5
• /
• pp.10-21
• /
• 2015

Many studies have been carried out on carbon fiber-reinforced plastic sheet(hereafter CFRP sheet)-confined concrete specimens for improve structural performance of concrete structures. To complement the existing studies, a parametric study is conducted to examine the effect of various design parameters such as layers of CFRP sheet, size and aspect ratio of specimens, and overlap length. The behavior of CFRP-confined concrete is compared using stress-strain curves of each specimen. And the strengthening effect of CFRP sheet is examined by maximum compressive strength. As the layers of CFRP sheet increases, structural performance of CFRP-confined concrete is significant increased. If the overlap length is more than 5% of circumstance, strengthening effect is not affected. In addition, a test database assembled from test results and existing studies is presented. Using these test database, accuracy and reliability of the existing strength models for CFRP-confined concrete are verified.

• International Journal of Concrete Structures and Materials
• /
• v.5 no.1
• /
• pp.49-55
• /
• 2011

The main objective of this investigation is to study size effect on compressive strength of CFRP confined concrete cylinders subjected to axial compressive loading. In total 24 concrete cylinders with different sizes were tested, small specimens with a diameter of 100 mm and a height of 200 mm, medium specimens with a diameter of 200 mm and a height of 400 mm, and big specimens with a diameter of 300 mm and a height of 600 mm. The lateral confining pressure of each specimen is the same and from that hypothesis the small specimens were confined with one layer of CFRP, medium and big specimens were performed by two and three layers of CFRP respectively. Test results indicate a significant enhancement in compressive strength for all confined specimens, and moreover, the compressive strengths of small and medium specimens are almost the same while a bit lower for big specimens. These results permit to conclude that there is no size effect on compressive strength of confined specimens regardless of cylinder dimension.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.5
• /
• pp.287-297
• /
• 2022

This paper presents experimental and analytical studies on the lateral cyclic behavior of RC columns actively confined with iron-based shape memory alloy (Fe-SMA) strips. Based on the Anexperimental study, we investigated the effectiveness of active confinement through compression testings of concrete cylinders confined by Fe SMA strips and carbon fiber-reinforced polymer (CFRP) sheets. The test results showed that the specimens confined with Fe SMA strips significantly increased the deformation capacity of the concrete, even under lower confining pressures, compared to those specimensconfined with CFRP sheets. The experimental results were used to develop finite-element models of RC columns confined with Fe SMA or CFRP in their plastic-hinge region. After validating the proposed analytical model through comparison with the results from a previous RC column test, a series of lateral cyclic load analyses were carried out for the RC columns confined with Fe SMA and CFRP. The analytical results revealed that the lateral cyclic behavior of the Fe SMA-confined column was greatly enhanced in terms of deformation and energy dissipation capacities compared with tothat of the as-built and CFRP-confined columns.

• Computers and Concrete
• /
• v.19 no.3
• /
• pp.233-241
• /
• 2017

During the last two decades, CFRP have been extensively used for repair and rehabilitation of existing structures as well as in new construction applications. For rehabilitation purposes CFRP are currently used to increase the load and the energy absorption capacities and also the shear strength of concrete columns. Thus, the effect of CFRP confinement on the strength and deformation capacity of concrete columns has been extensively studied. However, the majority of such studies consider empirical relationships based on correlation analysis due to the fact that until today there is no general law describing such a hugely complex phenomenon. Moreover, these studies have been focused on the performance of circular cross section columns and the data available for square or rectangular cross sections are still scarce. Therefore, the existing relationships may not be sufficiently accurate to provide satisfactory results. That is why intelligent models with the ability to learn from examples can and must be tested, trying to evaluate their accuracy for composite compressive strength prediction. In this study the forecasting of wrapped CFRP confined concrete strength was carried out using different Data Mining techniques to predict CFRP confined concrete compressive strength taking into account the specimens' cross section: circular or rectangular. Based on the results obtained, CFRP confined concrete compressive strength can be accurately predicted for circular cross sections using SVM with five and six input parameters without spending too much time. The results for rectangular sections were not as good as those obtained for circular sections. It seems that the prediction can only be obtained with reasonable accuracy for certain values of the lateral confinement coefficient due to less efficiency of lateral confinement for rectangular cross sections.

• Steel and Composite Structures
• /
• v.21 no.2
• /
• pp.411-427
• /
• 2016

While the cyclic behaviour of fiber-reinforced polymer (FRP)-confined columns is studied rather extensively, the cyclic response especially the energy dissipation of FRP-confined damaged and undamaged square RC columns is not yet fully understood. In this paper, an experimental and numerical investigation was conducted to study the cyclic behavior of two different types of Carbon FRP (CFRP)-confined square RC columns: strengthened and repaired. The main variables investigated are initial damage, confinement of CFRP, longitudinal steel reinforcement ratio. The experimental results show that lower initial damage, added confinement with CFRP and longitudinal reinforcement enhance the ductility, energy dissipation capacity and strength of the columns, decrease the stiffness and strength degradation rates of all CFRP-confined square RC columns. Two hysteretic constitutive models were developed for confined damaged and undamaged concrete and cast into the non-linear beam-column fiber-based models in the software Open System for Earthquake Engineering Simulation (OpenSees) to analyze the cyclic behavior of CFRP-confined damaged and undamaged columns. The results of the numerical models are in good agreement with the experiments.

• Earthquakes and Structures
• /
• v.8 no.5
• /
• pp.1171-1190
• /
• 2015

Enhancement of strength and ductility is the main reason for the extensive use of FRP jackets to provide external confinement to reinforced concrete columns especially in seismic areas. Therefore, numerous researches have been carried out in order to provide a better description of the behavior of FRP-confined concrete for practical design purposes. This study presents a new approach to obtain strength enhancement of CFRP (carbon fiber reinforced polymer) confined concrete cylinders by applying artificial neural networks (ANNs). The proposed ANN model is based on experimental results collected from literature. It represents the ultimate strength of concrete cylinders after CFRP confinement which is also given in explicit form in terms of geometrical and mechanical parameters. The accuracy of the proposed ANN model is quite satisfactory when compared to experimental results. Moreover, the results of the proposed ANN model are compared with five important theoretical models proposed by researchers so far and considered to be in good agreement.