Confinement Of Concrete Columns Research Articles

Prediction of Axial Compression Behavior of Confined Concrete Columns Considering the Effect of Cryogenic Temperatures

Prediction of Axial Compression Behavior of Confined Concrete Columns Considering the Effect of Cryogenic Temperatures

Review and Assessment of Material, Method, and Predictive Modeling for Fiber-Reinforced Polymer (FRP) Partially Confined Concrete Columns.

The repairing and strengthening of concrete structures using external and internal partial confinements are inevitable in the construction industry due to the new standards and rapid developments. The conventional materials and methods of confinement are unable to meet modern safety and functional standards. The fiber-reinforced polymer (FRP) enhances the strength and ductility of deteriorating and new concrete columns by reducing lateral confinement pressure and resistance against seismic shocks. The precise methods of partial confinement are inevitable for effective FRP-concrete bonding, durability, and cost-effectiveness under different loading conditions and to cope with external environmental factors. Predictive modeling and simulation techniques are pivotal for the optimization of confinement materials and methods by investigating the FRP-concrete novel confinement configurations, stress-strain responses, and failure modes. The novel materials and methods for concrete columns' partial confinement lack high compressive strength, ductility, chemical attack resistivity, and different fiber orientation impacts. This review provides an overview of recent confinement materials, novel methods, and advanced modeling and simulation techniques with a critical analysis of the research gaps for partial FRP confinement of concrete columns. The current challenges and future prospects are also presented.

Strength, Durability and Finite Element Analysis of Hybrid Jute/Basalt Fiber Reinforced Polymer Confined Concrete Column under Axial Compression

Implementing retrofitting measures for a civil structure may guarantee its ongoing safety and operation, while also extending its lifespan. The present investigation focused on the examination of compressive axial loads on concrete columns that were confined by natural fiber reinforced polymer (FRP). In particular, concrete cylinders confined with jute and basalt fiber epoxy composites were evaluated for their strength and durability. Various strength tests were conducted on unconfined and, jute, basalt, and hybrid jute-basalt FRP confined concrete cylinders with varying thicknesses of the FRP layers. Effectiveness of these natural FRP systems in providing external confinement to concrete columns in various environmental conditions were investigated, including exposure to acidic, alkaline, seawater, and potable water environments. Test results demonstrated that external confinement with hybrid FRP wraps, i.e. with both jute and basalt fibers, enhanced the load-bearing and energy absorption capacities by 63.64 % and 287 %, respectively. The confinement effectiveness of FRP wrapped specimens were 213 %, 164 %, 166 % and 163 % respectively compared to the unconfined specimens after exposure to acidic, alkaline, seawater and potable water environments. These impressive outcomes may be ascribed to the intrinsic rigidity of hybrid fibers. Furthermore, a finite element analysis (FEA) model of FRP confined concrete columns was performed using ABAQUS software calibrated with the experimental data. A close agreement between the experimental results and the adopted numerical model was observed. The outcome of the study suggests that the confinement with natural FRP can be used as a prominent retrofitting technique for columns in a variety of environments which can thus enhance the durability and sustainability of civil constructions.

Stress-strain models for FRP-confined thermally damaged concrete

Fiber-reinforced polymer (FRP) jackets have been increasingly used for the strengthening and confinement of concrete columns. Despite extensive research efforts yielding various concrete confinement models that can be broadly classified as design- and analysis-oriented, an accurate model is lacking for the design of FRP-strengthened thermally damaged concrete columns. This paper presents a comprehensive review of existing experimental studies on FRP-confined thermally damaged concrete columns and collects a large database of the corresponding test results. Then, a theoretical analysis is conducted to evaluate the accuracy and reliability of typical concrete confinement models (originally proposed for undamaged concrete) through extensive comparisons with the corresponding test data. The analytical findings have revealed that none of the existing models can accurately predict the compressive behavior of FRP-confined thermally damaged concrete. Two novel confinement models, design-oriented and analysis-oriented, are proposed for FRP-confined thermally damaged concrete. These novel models have appropriately considered the effects of high-temperature exposure on the confining pressure of FRP jackets and the lateral deformation characteristics of thermally damaged concrete. The proposed models are then validated by comparing the model predictions with the corresponding test results, indicating that these models can accurately predict the compressive stress-strain responses and dilation behavior of FRP-confined thermally damaged concrete.

Variability Analysis of the Hysteretic Behavior of Fiber-Reinforced Polymer (FRP)-Confined Concrete Columns Based on a Secondary Development Model

A reasonable material hysteretic constitutive model has a significant influence on the seismic simulation results of structures. To better describe the hysteresis seismic performance of fiber-reinforced polymer (FRP)-constrained concrete, a new modified hysteresis constitutive model is proposed based on the existing model and with sufficient consideration of the drop section of the skeleton curve. The validity of the proposed model is verified by comparing with quasi-static experimental data of FRP-confined reinforced concrete (FRP-C RC) columns in the literature. Subsequently, the compressive strength of concrete is selected as a major variable, and a quasi-Monte Carlo method is utilized to generate random samples, which are substituted into the proposed modified model and some comparison models. Finally, the hysteretic behavior of FRP-C RC columns is analyzed from the perspective of the material strength variability. The results demonstrate that (1) The proposed hysteretic constitutive model is able to provide rational predictions of the hysteretic behavior of FRP-C RC columns, and the mean relative error of each specimen is less than 6%. It can be applied to carbon FRPs (CFRPs) and glass FRPs (GFRPs), as well as different cross-sectional forms such as cylindrical and square columns. (2) A large number of hysteretic behavior cases of FRP-C RC columns can be successfully analyzed from the perspective of concrete material variability combined with finite element software. The average and variation coefficient of the maximum horizontal force of FRP-C reinforced C30 concrete columns are 76.77 kN and 0.0488, respectively, while the average and variation coefficient of the maximum horizontal force of FRP-C reinforced C50 concrete columns are 91.14 kN and 0.0454, respectively. (3) The average value and variation coefficient of the maximum horizontal force and equivalent damping ratio of FRP-C RC columns are affected by the compressive strength, axial compression ratio and reinforcement ratio, which show a certain regularity.

Comparative study of carbon and glass fiber reinforced polymer composites for the confinement of concrete columns

This study deals with the comparison of unconfined concrete specimens with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) confined concrete specimens using epoxy as matrix. Initially, CFRP, GFRP and epoxy laminates were prepared for the analysis of various mechanical properties like tensile strength, flexural strength and fracture toughness. From the test results, CFRP and GFRP laminates exhibit better properties than neat epoxy laminate. Axial compressive strength, energy absorption characteristics, failure modes of the confined specimens are analyzed. Comparing with unconfined specimens, it is noticed that the axial load carrying capacity of GFRP confined specimens increased by 23%. While the CFRP confined specimen is compared, a considerable enhancement of 57% was noticed with a confinement effectiveness of 1.57. It is observed that confinement by the FRPs can also increase the fracture energy and ductility index significantly, which can avert the catastrophic failure of the structures.

Use of Waste Tires as Transverse Reinforcement and External Confinement in Concrete Columns Subjected to Axial Loads

Approximately 246 million waste tires are generated annually in the United States. That is roughly three tires per four individuals in the country. Most tires end up in landfills, adversely affecting the environment. In the last two decades, researchers have explored using tire chips in concrete to replace a portion of coarse aggregates. Past studies have indicated that up to 50% of coarse aggregates in concrete can be replaced with tire chips. This research proposes using recycled rubber tires and rubber chips in concrete columns. The tires are used as external transverse reinforcement in plain concrete columns. The tires function as formwork during the pour while providing confinement after curing. The concepts in this research can be used for retrofitting structures with inadequate foundations and constructing new structures. After analyzing the data from this research, the axial compressive test of confined columns was 50% greater on average than unconfined columns. The confinement effectiveness ratio for all confined specimens was greater than one.

A Numerical Study addressing the Stress Distribution in Circular Steel Tube Confined Concrete Columns considering Various Concrete Strengths

The axially compressive behavior of Steel Tube Confined Concrete (STCC) columns has been experimentally investigated by many researchers throughout the world. However, it is extremely complicated to measure the stresses of steel tubes and concrete core in real tests. Therefore, to investigate the fundamental behavior of STCC columns under axial compression, this paper presents a numerical study that explores the stress distribution in steel tubes and concrete core. The circular STCC columns with the use of Normal Strength Concrete (NSC), High Strength Concrete (HSC), and Ultra-High Strength Concrete (UHSC) were simulated in a Finite Element Model (FEM) in ABAQUS. The material model for confined concrete incorporating a wide range of concrete strength values was developed in the simulation. The obtained from FEM curves of load versus strain of circular STCC columns were compared with those measured in real tests to verify the accurateness of the FEM. Deriving from the results of FEM, the stress states and their distribution in outer steel tubes and concrete core along the column height were described. Also, the longitudinal stresses on the cross-section of the concrete core were calculated corresponding with the load stage to quantify the strength enhancement of the concrete core due to the confinement effect from the steel tube. Furthermore, the confining pressure provided by the outer steel tube and impacting on the concrete core was plotted. Based on the findings in this paper, the effect of various concrete strengths on the stress distribution in circular STCC columns was investigated.

Experimental studies on confined compressive strength of Stainless Steel Wire Mesh (SSWM) wrapped concrete columns

The findings of an experimental evaluation of the axial compressive strength of an M25 grade Plain Cement Concrete (PCC) column confined with locally available Stainless Steel Wire Mesh (SSWM) are presented in this paper. Various types of Fiber Reinforced Polymer (FRP) are usually employed to strengthen the load-bearing components of concrete structures. However, these FRP materials exhibits brittle failure and debonding of FRP strip or wrap. Stainless Steel Wire Mesh (SSWM), on the other hand, is a cost-effective substitute for FRP materials when it comes to strengthening of structural elements. In this study, effectiveness of SSWM for confinement of concrete columns is demonstrated through experimental study. For the research, column specimens with a diameter of 150 mm and a height of 300 mm are used. Test specimens are strengthened with one-layer circumferential wrap of SSWM. Three variants of SSWM i.e. SSWM 30 × 32, SSWM 40 × 32 and SSWM 50 × 34 are considered for the study. After 28 days of moist curing, SSWM is applied to the column surface using epoxy SIKADUR 30LP. Axial compressive load-carrying capacities of strengthened specimen are compared with that of control specimens. From the comparative study it is found that SSWM 40 × 32 performs better compared to other variants of SSWM considered for this study. Compared to the control specimen, the load-carrying capacity of the column strengthened with SSWM 40 × 32 is increased by 29.35%. For all the specimen, failure patterns are observed in addition to the load–displacement and stress–strain behaviour. Results of present experimental investigation establishes the suitability of SSWM for confinement or strengthening of concrete elements subjected to compression.

Experimental Axial Compressive Behavior of Partially Confined Concrete Columns with Combined External and Internal FRP Strips

Experimental Axial Compressive Behavior of Partially Confined Concrete Columns with Combined External and Internal FRP Strips

Study of Behaviour of Short Concrete Columns Confined with PVC Tube under Uniaxial Load

An experimental investigation has been carried out to evaluate the effectiveness of Polyvinyl chloride (PVC) confinements in short plain circular concrete columns. The experimental part is conducted using different PVC tube diameters (110, 160, 220, and 250 mm) with two types of confinement strategies (fully and confined with the cut ends). The results are validated with unconfined samples (control samples). The test results showed that using external confinement of concrete columns by PVC tubes enhances the ultimate load capacity of the short columns. For fully confined samples, the enhancement ratio ranges between 5% and 8.3%, and from 4.16% to 15% for samples with cut ends. Furthermore, the confining of PVC pipes with the cut ends (CCC) has a more considerable effect on load capacity for all diameters except the ones with 250 mm, where the samples with full confinement (Cc) carried a bigger load than those with cutting ends. Finally, a numerical simulation of samples is carried out by the finite element (FE) model using the ABAQUS software. For all scenarios, the results of the numerical analysis showed considerable similarity to the experimental results, with R2 of 0.95 indicating the high linearity between the actual and simulated compressive strength values. Moreover, the FE induces fewer simulated errors with a relative error (RE) ranging from 0.16% to 6% for all scenarios.

Experimental and Numerical Investigations on Seismic Behavior of RC Beam to PVC-CFRP Confined Concrete Column Exterior Joint with Steel Tube Connector

Recently, substantial investigations were developed on a polyvinyl chloride (PVC)-carbon fiber-reinforced polymer (CFRP) confined concrete (PFCC) structure owing to its superior mechanical behavior and durability. However, a convenient and effective joint configuration between the PFCC columns and reinforced concrete (RC) beams still requires in-depth study. In the present work, the seismic performance of an RC beam to PFCC column exterior joint with steel tube connector (STC) is systematically studied. Eleven joint specimens are fabricated and tested, with the steel ratio of STC, reinforcement ratio of the frame beam, axial compression ratio, stirrup ratio of the joint and CFRP strips spacing as the design parameters. The experimental results, that is, 8 the failure modes, hysteretic response, ductility, strength, stiffness and energy dissipation, are analyzed. All specimens exhibit joint shear failure, although the joints with STC exhibit significantly better performance those of ordinary joint. In addition to reducing the axial compression ratio, the reinforcement ratio of the frame beam or increasing the stirrup ratio of the joint can also produce a positive effect. Furthermore, the numerical analysis of the exterior joints is performed; the calculated skeleton curves agree well with the test results, and additional parametric studies (i.e., the diameter, height and concrete strength of the joint) are carried out based on the verified numerical model.

The Strength in Axial Compression of Aluminum Alloy Tube Confined Concrete Columns with a Circular Hollow Section: Experimental Results

Steel tube confined concrete (STCC) stub columns have great strength and facilitate construction. In this study, the axial compressive strength of an aluminum alloy tube confined concrete column with (ATCC-CHS) and without (ATCC) a circular hollow section was tested in laboratory experiments. The influence of concrete strength, diameter–thickness ratio and the hollow rate on the failure mode, ultimate compressive strength, strain, stiffness, constraint effects and ductility was quantified. The experiments showed that local buckling failure could be effectively delayed when the outer aluminum tube did not directly bear axial load. Columns without a circular hollow section had bearing capacities approximately 20% higher than those with a circular hollow section, though their ductility was poorer. The ultimate strength tended to increase with decreases in the hollow rate and diameter–thickness ratio. It tended to increase with increasing concrete strength, though stronger concrete also reduced ductility. The bearing capacities of the columns were calculated according to several proposed formulas and compared with the experimental results, and the proposed Teng and Attard’s formula appeared to be satisfactory.

Experimental and Numerical Study on Uniaxial Compression Failure of Concrete Confined by Nylon Ties

The developments in the cisvil engineering fields have led to an increased demand for structural reinforcements. Therefore, designing an effective, green, convenient, and low-cost reinforcement method is considerably important. Nylon ties have high strength and good heat resistance, and they can retain good tensile properties after high-temperature cooling. Further, they are inexpensive and can be recycled. Thus, they are considered suitable for structural reinforcement engineering. In this study, the core concrete was reinforced by the active confinement of prestressed nylon ties. A uniaxial compression test was performed to evaluate the reinforcement effect of the preload generated by the high-temperature cooling of the tie rod on the core concrete. The results show that nylon ties can effectively improve the mechanical properties of the core concrete. Combined with numerical simulation technology, a damage model of a confined concrete column (CC) was established, and the damage evolution law of CC under uniaxial axial compression was analyzed. Combined with numerical simulation and experimental research, the effectiveness of nylon tie reinforced concrete and the reliability of the damage model were verified, providing a reference for research on engineering reinforcement.

Accuracy of models of concrete in circular columns using different proposals for the prediction of failure of the confining FRP

Confinement of concrete columns with fiber reinforced polymers results in an increase of strength and ductility. For this reason, the use of aramid, carbon and glass-based composites for confinement of reinforced concrete columns has significantly increased over the last decades. Nevertheless, few models adequately predict the failure strain of the fiber reinforced polymer, which has a determinant influence on the computed results. In this paper the accuracy of existing models of confined concrete using different proposals for the prediction of the failure strain of the confining composite is assessed. This is based on the comparison of analytical results with experimental test results of concrete columns with circular cross-section reported in the literature. The comparison focusses on different parameters such as strength, maximum strain and strain energy density.

Behavior of Confined Concrete Columns with Hssswr Meshes Reinforced Ecc Jacket Under Uniaxial Compression

Behavior of Confined Concrete Columns with Hssswr Meshes Reinforced Ecc Jacket Under Uniaxial Compression

Experimental Study on the Confinement of Concrete Cylinders with Large Rupture-Strain FRP Composites

Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites, typically formed from polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) fibers, generally exhibit ultimate rupture strains >5%. Such fibers are particularly suited to the confinement of concrete columns on account of their LRS and sufficient elastic modulus. There are currently a limited number of studies on LRS FRP-confined concrete, particularly with high- and ultrahigh-strength concrete, so their behavior across a range of variables is still unknown. To improve this understanding, this paper systematically investigates the influence of fiber type, fiber thickness, and concrete strength on the behavior of FRP-confined concrete. To achieve this objective, the current investigation presents the results of 66 circular FRP-confined cylinders that are loaded concentrically. Three main parameters are investigated, namely, fiber type (i.e., PEN, PET, carbon, glass, and aramid), concrete strength (i.e., normal, high, and ultrahigh strength), and fiber thickness. The results show that regardless of fiber type, the stress–strain response is bilinear when the concrete is sufficiently confined. However, when there is insufficient confinement provided to the concrete core, the stress–strain response becomes trilinear. This trilinear response is more pronounced for LRS FRP-confined specimens because the confinement stiffness of the LRS FRP jacket is lower than that of a traditional FRP-confined specimen with an equivalent confinement ratio. Increasing the confining hoop stiffness (i.e., increasing FRP layers) reduces the magnitude of strength reduction after initial concrete cracking. It is also evident that as the unconfined concrete strength increases, the minimum confinement stiffness ratio necessary to prevent strength reduction after initial concrete cracking increases.

Compressive Stress-Strain Model for Laterally Confined Concrete Columns with Steel Fibrous Composites

Compressive Stress-Strain Model for Laterally Confined Concrete Columns with Steel Fibrous Composites

Finite Element Analysis on Weak PVC-FRP Confined Concrete Column and Strong Joint Strengthened with Core CFST Under Axial Compression

Finite Element Analysis on Weak PVC-FRP Confined Concrete Column and Strong Joint Strengthened with Core CFST Under Axial Compression

Study of minimum requirements of confinement in concrete columns confined with WRG in moment resisting frames

The national concrete standard SNI 2847:2013 which refers to the ACI 318M-11 has not accommodated the influences of the axial load and deformation parameters as performance requirement, where both parameters are very critical to affect the required confining steel of concrete columns. This study presents the test results of reinforced concrete columns confined with WRG which were designed according to ACI standards. The test results were analyzed using several codes such as SNI 2847:2013, ACI 318M-14, CSA A23.3-04, and NZS 3101-06 standards. Furthermore, the minimum confinement equation is proposed for the design of columns confined with WRG, then it is also compared with selected confinement provisions. The study results showed that the equation for confining reinforcement adopted in the SNI 2847:2013 or ACI 318-11 is very conservative compared to other codes when applied to low axial load levels (≤ 0.25 Agf’c), but relatively less conservative or unsafe if the axial load level is greater than 0.3. From result of evaluation show that CSA A23.3-04 provide most conservative result for confinement design. The additional confinement design equations at ACI 318M-14 has been improve confinement design of ACI Code. Compared with SNI requirements, which do not depend on the level of axial load on the column, the equations proposed here would allow reduced confining reinforcement for columns with higher axial load. Overall, the proposed equation presents the best correlation to actual drift capacity of columns, and in addition it can be used for columns reinforced with WRG-transverse reinforcement having a yield strength higher than 500 MPa. The study also provides the recommendation for further refinement of SNI 2847 in the future related to the requirement of WRG confinement in concrete columns of Special Moment Frames in highly seismic regions.