Confinement Of Concrete Columns Research Articles

Experimental investigation on behaviour of RC circular and square columns confined with natural fabrics

In this paper natural fibers are confined with short circular and square columns for strengthening purpose with conventional wrapping technology. The substitution of natural fibres for synthetic fibres is a new approach to achieve sustainable construction. The most commonly used fibers are Glass, Carbon, Aramid, etc., but the fibers are costly and considered to be slightly uneconomical. Hence natural fibers namely Jute, Kenaf and Flax are utilized in this research. An experimental study reports the efficacy of the use of Jute, Kenaf, and Flax fabrics as external confinement for concrete columns furthermore, the outcomes propose that a huge improvement in the quality properties. Circular columns of 100mm diameter and 600mm height have been constructed and are tested under axial compression. The test outcomes show that the axial load carrying limit of FRP wrapped is increased than the control columns by a significant percentage. In these three natural fibers, Flax FRP wrapped columns offer more strength than Jute and Kenaf fiber wrapped columns. Natural fibers not only increase the strength it is cost-effective and environmental friendly as they are 100% bio-degradable.

Deformations of a plastic tube with concrete-infill under direct load

Confinement of concrete columns can be an effective means of enhancing structural members' deformation—alternative materials such as uPVC tube show elastic-plastic behavior with considerable elongations at failure. The material ductility features significant deformations that usually considered to be belonging to the set of mechanical properties. The tube can be applied for encasing concrete, thereby influencing the deformability capacity of a column. The current work aims to evaluate the axial strain of plastic tubes with concrete-infill (PTCI) specimens tested under uniaxial compression load. A strain model was developed for PTCI specimens using a normalized confinement stiffness procedure, based on a database of experimental results from recent studies 2019-2020 and those of the present study. Five existing FRP-confined concrete models and the developed model were employed to predict PTCI columns' strain, and the predictions were compared with experimental results in the database. Three statistical indexes were used to evaluate the proposed and the three existing FRP-confined concrete strain models' performance. The indexes included: Average absolute relative error (AAE), Normalized root-mean-square error (NRMSE), and coefficient of correlation (R2). The comparison shows the proposed model to give more close prediction to the experimental test data and the comprehensive database to yield the lowest average absolute error (AAE). The root means square error (RMSE) compared with other models in the present study.

Compressive Strength of FRP-Reinforced and Confined Concrete Columns

Nowadays, the practice of fiber-reinforced polymers (FRPs) as an internal reinforcement and external wrapping has been expanded in the construction industry. No theoretical model for estimating the compressive strength (CS) of FRP bars reinforced concrete (RC) columns wrapped with FRP sheets (FRCFS columns) has been found in the literature. The main goal of the current research work is to recommend a new theoretical model for estimating the CS of FRCFS columns. To secure the aims of the present work, the previous research works were employed to construct two different records. The first record consists of 500 sample points of FRP-wrapped concrete specimens, and the second record consists of 269 sample points of FRP bars RC columns. Some initial assessments were carried out on the collected records to select the most suitable forms of the recommended models for FRP-wrapping and CS of FRP bars RC columns. The estimations of these models presented higher accuracy as compared with the previously recommended models. Finally, a new theoretical model was recommended for the CS of FRCFS columns. Then, an extensive parametric study of 216 specimens of FRCFS columns was carried out using the recommended theoretical model.

Compressive strength of concrete confined with fabric reinforced cementitious matrix (FRCM): Analytical models

Composite materials employing cement-based mortars, usually known as fabric-reinforced cementitious matrix (FRCM) composites, have recently emerged as an attractive solution for the repairing and strengthening of reinforced concrete or masonry members. They represent a promising alternative to the use of Fiber Reinforced Polymer (FRP) composites when there is a need to overcome some of the drawbacks related to the epoxy resin, such as moderate matrix heat and fire resistance, difficulty of application at low temperatures, impossibility of application on wet surfaces, and lack of vapor permeability. This paper presents an analytical study on the confinement of concrete columns with FRCM composites with the twofold objective to: (a) propose new models for the estimate of the compressive strength, and (b) assess existing models available in the literature and in some international guidelines.To this purpose, a wide database including results of compression tests performed on over 290 concrete cylinders externally wrapped with FRCM was assembled from the literature. The collected results were employed to perform an overall analysis of the efficiency of the FRCM confinement by varying some of the relevant parameters, such as: type of fiber (glass, carbon, steel, PBO or basalt) and geometry of the mesh, number of employed layers, mechanical properties of the inorganic matrix and compressive strength of the unconfined concrete. Relationships for estimating the compression strength of the FRCM confined concrete were then developed through best-fit analyses, and comparisons with some formulations available in the literature and in some international guidelines were performed.

Analytical model of large-scale circular concrete columns confined by pre-stressed carbon fibre reinforced polymer composites under axial compression

In recent years, for the reinforcement of concrete structures, fibre-reinforced polymers have been extensively employed, thus enhancing the structural properties of the reinforced materials. This paper presents a pre-stressing strengthening method for the confinement of large-scale circular concrete columns. The axial compressive behaviour of confined columns was tested and analysed. The experimental and analytical results indicated that the stiffness, ductility, and bearing capacity of reinforced concrete (RC) columns strengthened with pre-stressed carbon fibre-reinforced polymer (CFRP) composites were significantly higher than those of non-prestressed columns. A theoretical relationship between the peak strength and bearing capacity of large-scale RC columns actively confined by pre-stressed CFRP composites was proposed. A tri-linear stress-strain model for the actively confined large-scale concrete columns was presented and compared with the experimental results. Moreover, the model is sufficiently simple for use in design. The results of the proposed model were compared with the experimental results of small-scale columns, and the influence of size was found to be critical to the analysis of RC columns confined by pre-stressed CFRP composites.

Nonlinear finite element modelling of concrete columns confined with textile reinforced mortar

Textile reinforced mortar (TRM) is an innovative material developed to overcome the limitations of fibre reinforced polymer (FRP). It consists of high strength textile fibre mesh embedded in cementitious binder which is organic in nature and compatible with concrete substrate. This paper presents the development of a finite element model for confinement of concrete columns using TRM. Concrete damaged plasticity model was used to represent the behaviour of TRM. The model accounts for nonlinear material behaviour in concrete core and mortar. The model was validated against experimental result from literature. Maximum divergence between experimental and numerical results was 5%. Following the validation, the developed model was used to carry out parametric studies on circular and square column confinement. The thickness of mortar layer, cross section shape of the core and corner radius of square column were considered in the study to gain a profound knowledge of the confinement and to study its influence on the behaviour of confined concrete column.

Reliability analysis of proposed capacity equation for predicting the behavior of steel-tube concrete columns confined with CFRP sheets

Due to higher stiffness to weight, higher corrosion resistance, higher strength to weight ratios and good durability, concrete composite structures provide many advantages as compared with conventional materials. Thus, they have wide applications in the field of concrete construction. This research focuses on the structural behavior of steel-tube CFRP confined concrete (STCCC) columns under axial concentric loading. A nonlinear finite element analysis (NLFEA) model of STCCC columns was simulated using ABAQUS which was then, calibrated for different material and geometric models of concrete, steel tube and CFRP material using the experimental results from the literature. The comparative study of the NLFEA predictions and the experimental results indicated that the proposed constitutive NLFEA model can accurately predict the structural performance of STCCC columns. After the calibration of NLFEA model, an extensive parametric study was performed to examine the effects of different critical parameters of composite columns such as; (i) unconfined concrete strength, (ii) number of CFRP layers, (iii) thickness of steel tube and (iv) concrete core diameter, on the axial load capacity. Furthermore, a large database of axial strength of 700 confined concrete compression members was developed from the previous researches togive an analytical model that predicts the ultimate axial strength of composite columns accurately. The comparison of the predictions of the proposed analytical model was done with the predictions of 216 NLFEA models from the parametric study. A close agreement was represented by the predictions of the proposed constitutive NLFEA model and the analytical model.

Test and simulation of circular steel tube confined concrete (STCC) columns made of plain UHPC

This study presents experimental and numerical investigations on circular steel tube confined ultra high performance concrete (UHPC) columns under axial compression. The plain UHPC without fibers was designed to achieve a compressive strength ranged between 150 MPa and 200 MPa. Test results revealed that loading on only the UHPC core can generate a significant confinement effect for the UHPC core, thus leading to an increase in both strength and ductility of columns, and restricting the inherent brittleness of unconfined UHPC. All tested columns failed by shear plane failure of the UHPC core, this causes a softening stage in the axial load versus axial strain curves. In addition, an increase in the steel tube thickness or the confinement index was found to increase the strength and ductility enhancement and to reduce the magnitude of the loss of load capacity. Besides, steel tube with higher yield strength can improve the post-peak behavior. Based on the test results, the load contribution of the steel tube and the concrete core to the total load was examined. It was found that no significant confinement effect can be developed before the peak load, while the ductility of post-peak stage is mainly affected by the degree of the confinement effect. A finite element model (FEM) was also constructed in ABAQUS software to validate the test results. The effect of bond strength between the steel tube and the UHPC core was also investigated through the change of friction coefficient in FEM. Furthermore, the mechanism of circular steel tube confined UHPC columns was examined using the established FEM. Based on the results of FEM, the confining pressures along the height of each modeled column were shown. Furthermore, the interaction between the steel tube and the UHPC core was displayed through the slip length and shear stresses between two surfaces of two materials.

Structural performance of novel SCARC column under axial and eccentric loads

A novel spiral confined angle-steel reinforced concrete (SCARC) column was developed in this study. A total of 16 specimens were prepared and tested (eight of them were tested under axial loading, the other eight were tested under eccentric loading). The failure processes and load-displacement relationships of specimens under axial and eccentric loads were examined, respectively. The load-carrying capacity and ductility were evaluated by parametric analysis. A calculation approach was developed to predict the axial and eccentric load-carrying capacity of these novel columns. Results showed that the spiral reinforcement provided enough confinement in SCARC columns under axial and low eccentric loads, but was not effective in that under high eccentric loads. The axial load-carrying capacity and ductility of SCARC columns were improved significantly due to the satisfactory confinement from spirals. The outer reinforcement and other construction measures were necessary for SCARC columns to prevent premature spalling of the concrete cover. The proposed calculation approach provided a reliable prediction of the load-carrying capacity of SCARC columns.

Axial compressive behavior of confined steel fiber reinforced high strength concrete

Concrete is brittle in nature which is why different materials have been used to improve this inherent behavior of concrete. In this experimental study, the effect of simultaneous use of steel fibers and confinement on high strength concrete and the corresponding post peak response of fiber reinforced concrete is investigated. A total of 39 high-strength concrete (incorporating varying amounts of steel fibers) cylinders were casted. The steel fiber volume fraction (Vf) was varied as 0.5%, 1.5% and 2.5%. 18 samples were confined with Carbon Fiber Reinforced Polymer (CFRP) sheet, and 9 samples were casted in steel pipe confinement, whereas 12 control specimens (without confinement) were also prepared. The samples were tested under axial compression. The results confirmed that the use of steel fiber had minute effect on the compressive strength, whereas it significantly improved the ductility and enhanced the post peak behavior of concrete. The confinement significantly contributed towards the compressive strength increase. The combined use of steel fibers and confinement in concrete columns can be viewed as extremely beneficial as it not only increases the concrete compressive strength but also solves the issue of brittle failure to an appreciable extent.

Compression Splices of GFRP Bars in Unconfined and Confined Concrete Columns

AbstractAlthough the use of glass fiber–reinforced polymer (GFRP) bars as compression reinforcement in RC columns has been extensively investigated, no research has been conducted on spliced GFRP b...

Experimental studies and theoretical models for concrete columns confined with FRP composites: a review

PurposeAdvanced fibre-reinforced polymer (FRP) composites have been increasingly used over the past two decades for strengthening, upgrading and restoring degraded civil engineering infrastructure. Substantial experimental investigations have been conducted in recent years to understand the compressive behaviour of FRP-confined concrete columns. A considerable number of confinement models to predict the compressive behaviour of FRP-strengthened concrete columns have been developed from the results of these experimental investigations. The purpose of this paper is to present a comprehensive review of experimental investigations and theoretical models of circular and non-circular concrete columns confined with FRP reinforcement.Design/methodology/approachThe paper reviews previous experimental test results on circular and non-circular concrete columns confined with FRP reinforcement under concentric and eccentric loading conditions and highlights the behaviour and mechanics of FRP confinement in these columns. The paper also reviews existing confinement models for concrete columns confined with FRP composites in both circular and non-circular sections.FindingsThis paper demonstrates that the performance and effectiveness of FRP confinement in concrete columns have been extensively investigated and proven effective in enhancing the structural performance and ductility of strengthened columns. The strength and ductility enhancement depend on the number of FRP layers, concrete compressive strength, corner radius for non-circular columns and intensity of load eccentricity for eccentrically loaded columns. The impact of existing theoretical models and directions for future research are also presented.Originality/valuePotential researchers will gain insight into existing experimental and theoretical studies and future research directions.

Experimental Investigation of Axial Compressive Behavior of Large-Scale Circular Concrete Columns Confined by Prestressed CFRP Strips

AbstractOne important application of fiber-reinforced polymer (FRP) composites is providing confinement for concrete columns. Utilization of prestressed FRP sheets can relieve stress hysteresis thr...

Finite Element Analysis of Corner Strengthening of CFRP-Confined Concrete Column

Strengthening of the concrete structure is one of the most difficult and important tasks of civil engineering. This paper presented the application of nonlinear finite element models in the analysis of Corner Strengthening of CFRP- Confined Concrete Column by using ANSYS software. The finite element models are build using a smeared cracking approach for concrete material and three dimensional layered element for the CFRP composite. The numerical results are compared with the corresponding experimental results of columns. The results show that the stress- strain curve obtained from the analytical data using ANSYS are in good agreement with experimental data. In this paper, the parameters considered are: CFRP strip thickness and its elasticity modulus (locally added at corner column regions for strengthening) in addition to the corner column radius.

Hybrid FRP jacketing for enhanced confinement of circular concrete columns in compression

The main goal of the study herein described was to evaluate the performance of an innovative confining unidirectional hybrid FRP solution for circular concrete columns, exploiting the hybrid effect and pseudo-ductility of FRP jackets made of different fibres. First, an experimental study on the compressive stress-strain curves of small-scale plain circular concrete columns confined with hybrid FRP was conducted. Jackets were produced with dry unidirectional fabrics of high-modulus carbon, standard-modulus carbon, E-glass, and basalt. Different combinations were tested, varying the number of layers of each material. Next, two new simple design-oriented models were developed in order to predict the compressive peak stress of compressed concrete columns confined with hybrid FRP jacketing. Predictions were in close agreement with test results. Finally, an existing analysis-oriented model developed for non-hybrid FRP-confined concrete was adapted to also predict dilation and the compressive stress-strain curve of hybrid FRP-confined concrete. Likewise, predictions were in close agreement with test results. It was concluded that hybridisation can effectively contribute to maximize the lateral strain efficiency of FRP jacketing and its behaviour can be predicted with the developed analytical models.

Behavior of concrete columns confined with both steel angles and spiral hoops under axial compression

This study proposed a new type of concrete column that was confined with both steel angles and spiral hoops, named angle-steel and spiral confined concrete (ASCC) column. A total of 22 ASCC stub columns were tested under axial compression to investigate their behavior. For a comparison, three angle-steel reinforced concrete (ARC) stub columns were also tested. The test results indicated that ASCC column had a superior mechanical performance. The strength, ductility and energy absorption were considerably increased due to the improvement of confinement from spiral hoops. The confinement behavior and failure mechanism of ASCC column were investigated by the analysis of failure mode, load-deformation curve and sectionstrain distribution. Parametric studies were carried out to examine the influences of different parameters on the axial compression behavior of ASCC columns. A calculation approach was developed to predict the ultimate load carrying capacity of ASCC columns under axial compression. It was validated that the predicted results were in well agreement with the experimental results.

Fibre-reinforced polymer efficiency in square columns with different corner radii

Confinement of concrete columns by means of externally bonded fibre-reinforced polymer composites is a well-established technique for strengthening purposes. The corner effect is one of the most important parameters affecting the polymer composite efficiency in confined square and rectangular columns. In this work, non-linear finite-element analysis was used to investigate the behaviour of polymer-composite-confined square columns considering the effect of the corner radius. To compare the efficiency of polymer confinement for different corner radii, column specimens with corner radius-to-side dimension ratios between 0 and 0·5 were modelled and analysed. The Tsai–Wu failure criterion was used to examine the behaviour of the polymer composite under biaxial stresses. The results showed that increasing the corner radius provided more uniformly distributed confining stresses and also increased the polymer composite rupture strain, which improved its efficiency in confinement. Based on the results, in specimens with sharper corners, the interaction of biaxial stresses, hoop tension and axial compression, according to the Tsai–Wu failure criterion, causes maximum stress at the section corners. This leads to premature rupture of the polymer composite at these parts, thus reducing the efficiency of the composite.

Experimental Study on Fibre-reinforced Cementitious Matrix Confined Concrete Columns under Axial Compression

Experimental Study on Fibre-reinforced Cementitious Matrix Confined Concrete Columns under Axial Compression

Combined effect of CFRP-TSR confinement on circular reinforced concrete columns

The use of external carbon-fiber-reinforced polymer (CFRP) wraps is one of the most effective techniques existing for the confinement of the circular concrete columns. Currently, several researches have been made to develop models for predicting the behavior of this type of confinement. The disadvantage of the most models, is to not take into account the contribution of the transverse steel reinforcements (TSR) effect, However, very limited models have been recently developed that considers this combined effect and gives less accurate results. This paper presents the development of a new model for the axial behavior of circular concrete columns confined by combining external CFRP warps-and-internal TSR (hoops or spirals) based on the existing experimental data. The comparison between the proposed model and the experimental results showed good agreement comparing to the several existing models. Moreover, the expressions of estimating the ultimate strength and the corresponding strain are simple and precise, which make it easy to use in the design applications.

Concrete Columns Wrapped with Hemp Fiber Reinforced Polymer – An Experimental Study

Concrete confinement with Fiber reinforced polymers (FRP) is a method widely used for strengthening and rehabilitation purposes. The replacement of synthetic fibers with natural fibers is a step to achieve a sustainable construction. In this research, an experimental study reports the efficacy of the use hemp FRP as external confinement for concrete columns and the effect of different parameters that may affect the structural behavior of concrete columns confined with FRP. The test variables are: the number of confining layers, and the columns slenderness ratio. Uniaxial compression test was done for a total number of 30 specimens. The axial stress-strain curves, structural ductility measured by fracture energy and failure modes were analyzed. Also, the applicability of existing stress and strain models available in the literature is checked. It was found that the number of confining layers and columns slenderness ratio have a significant effect on the confinement effectiveness and ductility. This study gave promising results vis-à-vis the use of natural fibers as external confinement despite the tensile strength of hemp FRP that are significantly lower than that of synthetic FRP.