Compression Behavior Of Concrete Columns Research Articles

Compression behavior of concrete columns combinedly confined by FRP externally wrapped Fe-SMA strips

Compared to the traditional passive confinement to strengthen concrete columns, previous studies testified that the active confinement provided by prestressed materials not only can improve certainly the material utilization rate, but also alleviate the hysteresis of confinement stress. Meanwhile, the iron-based shape memory alloy (Fe-SMA), that performs the shape memory effect, can be utilized as an innovative strengthening method to rapidly apply the active confinement on concrete columns. In this paper, an innovative active strengthening method by using Fe-SMA strips was proposed, which can provide the potential to make emergency repairing for the damaged columns after the earthquake or impact. The compressive behavior of concrete columns separately confined by the passive confinement, the active confinement, and the hybrid confinement was researched by the compression test, and the different net-spacing strips and different layers of FRP strips were considered as well. The compression test was used to explore the compressive behavior of concrete columns that were confined by three different methods: passive confinement, active confinement, and hybrid confinement, and the test also considered different spacing distance strips and different FRP layers. According to the results, these three confinement types can effectively enhance the load carrying capacity and corresponding deformation of stub columns, especially the hybrid confinement. Finally, a verifying calculation was proposed to predict the peak compressive stress of these specimens, serving as a reference for selecting appropriate methods to strengthen concrete columns.

Effect of tie spacing and GFRP rebar diameter on compression behavior of concrete columns

Effect of tie spacing and GFRP rebar diameter on compression behavior of concrete columns

Experimental study on eccentric compression behavior of slender rectangular concrete columns reinforced with steel and BFRP bars

This study aims to investigate the eccentric compression behavior of concrete columns reinforced with a hybrid of steel and basalt fiber-reinforced polymer (BFRP) bars and ties (hybrid-RC). A total of ten slender columns were constructed and tested, including six hybrid-RC columns, two longitudinal steel bars and ties reinforced concrete (steel-RC) columns, and two longitudinal BFRP bars and ties reinforced concrete (BFRP-RC) columns. The study focused on the effects of reinforcement type, loading eccentricity, and reinforcement ratio. The test results indicated that the hybrid-RC columns with relatively higher reinforcement ratios demonstrated close load-carrying capacity and stiffness to those of steel- and BFRP-RC columns. All the columns experienced a significant reduction in their load-carrying capacities, as well as the axial and lateral stiffness, when the applied loading eccentricity increased from 80 mm to 150 mm. As the reinforcement ratio increased, hybrid-RC columns exhibited an improvement in the load-carrying capacity, stiffness, and axial force contribution of longitudinal bars in compression. Furthermore, the equations to predict the cross-sectional strength of hybrid-RC columns were proposed by theoretical analysis, and the existing methods considering the slenderness effect were evaluated for hybrid-RC columns.

Compression Behavior of Concrete Columns Strengthened with Fiber-Reinforced Inorganic Composites Based on Magnesium Phosphate Cement.

Fiber-reinforced polymer (FRP) composites have become attractive for strengthening and repairing deteriorated concrete structures. However, their poor high-temperature resistance and durability in some extreme environments, such as frequent water-vapor erosion and temperature changes, limit their application. Magnesium phosphate cement (MPC) has been used to repair damaged concrete due to its excellent high-temperature resistance and durability. Therefore, this paper aims to study the compressive behavior of concrete columns strengthened with fiber-reinforced inorganic polymer (FRiP) composites based on magnesium phosphate cement so as to evaluate the confinement effect. Twenty-one cylindrical specimens were prepared to examine the axial compressive behavior of carbon-fiber-reinforced inorganic polymer (CFRiP) specimens based on magnesium phosphate cement confined by one to three layers of carbon-fiber fabrics. They are compared with concrete specimens strengthened with epoxy-based FRP and unconfined concrete specimens. The test results show that compared with the unconfined concrete specimen, the strength of the CFRiP-strengthened specimens based on magnesium phosphate increases by 1.69-2.50 times, and their ultimate strain is enlarged by 1.83-3.50 times. The strength and ultimate strain of the CFRiP-strengthened specimens based on magnesium phosphate are approximately 95% and 60% of those of the specimens strengthened with epoxy-based FRP, respectively. A semiempirical model of concrete confined by the CFRiP system based on magnesium phosphate cement is also proposed. The theoretical prediction is finally compared with the experimental results, indicating that the developed model provides a prediction close to the test results.

Study on Eccentric Compressive Behavior of Concrete Columns Reinforced with NPR735 High-Strength Steel Bars

In this paper, eccentric compressive tests and theoretical studies of grade 735 MPa reinforced concrete columns were conducted. The eccentric distance and strength of the longitudinal reinforcement were used as experimental parameters to investigate the bearing capacity, failure mode, and strength of eccentric compressive behavior of NPR735 high-strength steel bars. When the load eccentricity of the reinforced concrete columns was small or longitudinal, the reinforcement ratio was large, and small eccentricity failure occurred. The results were similar to the failure mode of ordinary concrete columns with traditional steel bars. When the load eccentricity decreased, the bearing capacity increased, but the deflection and ductility of the specimen decreased. When the strength of the longitudinal reinforcement increased, the bearing capacity of the specimen increased slightly. Finally, according to current design methods in the concrete structure design code, the bearing capacity of the eccentric compressive column was obtained, and the calculated results were compared with the experimental results to verify the applicability of the concrete structure design code GB50010-2010 to concrete columns with grade 735 MPa reinforcement.

Compression behavior of concrete columns strengthened by a hybrid BFRP/HDPE tube coupled with a crumb rubber concrete cladding layer

A previous study proved that the confinement of fiber-reinforced polymer (FRP) effectively improves the load capacity and ductility of concrete columns. High-density polyethylene (HDPE) material, which exhibits excellent erosion resistance and high ductility, possesses enormous potential for strengthening structural columns. Based on the discussion, the combination of these two materials as hybrid confinement is investigated in this study. As an energy-dissipating material with excellent ductility, rubber concrete is employed in the hybrid strengthening method as an anti-collision layer. A novel composite system that comprises external FRP-HDPE confinement and an infilled rubber concrete layer is proposed in this study. An experimental test investigates its compressive strength, and three variables are considered, including the diameter of the HDPE tube, the layers of FRP sheets, and the addition of rubber particles in rubber concrete. The test results show that the ultimate compressive strength of specimens is improved with an increase in the diameter of the HDPE tube and layers of the FRP sheet, while the higher addition of rubber particles can reduce the compressive strength. However, these three variables have a positive effect on the deformation capacity of the specimens. A theoretical model is proposed for predicting the ultimate axial stress of specimens, which can provide a reference for designing this hybrid reinforcement.

Experimental and analytical study on eccentric compressive behavior of concrete columns strengthened with high-strength reinforcement of HRB600

This study examines the influence of initial eccentricity, volume stirrup ratio, and the strength of longitudinal reinforcement and stirrup on the eccentric compressive performance of concrete columns strengthened with HRB600-high-strength-reinforcement. Ten concrete columns are tested under eccentric compression. The compressive mechanism evaluates and compares the failure characteristics, load-deformation curve, reinforcement strain, and eccentric compression performance. As part of the numerical study, the finite element modeling of OpenSees is used to predict the response of HRB600 specimens under eccentric compressive loading, and parametric analysis is subsequently conducted. The research findings illustrate that HRB600 longitudinal reinforcement can yield in tension and compression with large eccentricity when approaching the ultimate bearing capacity state. After normal strength longitudinal reinforcement is supplanted, the reinforcement amount is saved. Lastly, semi-empirical models have been proposed to predict the compressive performance of concrete columns with high-strength reinforcement.

Compressive Behavior of Corroded RC Columns Strengthened With Ultra-High Performance Jacket

This paper performed compressive tests on corroded reinforced concrete (RC) columns with externally confined ultra-high performance concrete (UHPC) jacket. The studied parameters in this testing program was the corrosion ratio of specimens. The influences of this parameter on the compressive behavior of concrete columns confined by UHPC jacket was reported and discussed. The test results revealed that when the rust rate was less than 20%, axial cracking was the typical failure mode of unreinforced specimens, and the cracks in the rusted area gradually increased with the increase of the rust rate. When the corrosion rate reached 30%, the concrete of the protective layer fell off significantly, and the longitudinal reinforcement also yielded. The ultimate load and peak displacement of the specimens reinforced with UHPC were significantly improved, and the improvement rates of the two were more than 80% and 30%, respectively. The failure mode of the specimen with a corrosion rate of 30% also changed to longitudinal cracking of the UHPC layer. An analytical model was proposed to predict the ultimate load of RC columns with externally strengthening UHPC jacket. The validations of the predictions against the reported test results confirmed the accuracy of the analytical model.

Influence of the Cross-Sectional Shape and Corner Radius on the Compressive Behaviour of Concrete Columns Confined by FRP and Stirrups.

Axial compression tests were carried out on 72 FRP (fiber reinforced polymer)–stirrup composite-confined concrete columns. Stirrups ensure the residual bearing capacity and ductility after the FRP fractures. To reduce the effect of stress concentration at the corners of the confined square-section concrete columns and improve the restraint effect, an FRP–stirrup composite-confined concrete structure with rounded corners is proposed. Different corner radii of the stirrup and outer FRP were designed, and the corner radius of the stirrup was adjusted accurately to meet the designed corner radius of the outer FRP. The cross-section of the specimens gradually changed from square to circular as the corner radius increased. The influence of the cross-sectional shape and corner radius on the compressive behaviour of FRP–stirrup composite-confined concrete was analysed. An increase in the corner radius can cause the strain distribution of the FRP to be more uniform and strengthen the restraint effect. The larger the corner radius of the specimen, the better the improvement of mechanical properties. The strength of the circular section specimen was greatly improved. In addition, the test parameters also included the FRP layers, FRP types and stirrup spacing. With the same corner radius, increasing the number of FRP layers or densifying the stirrup spacing effectively improved the mechanical properties of the specimens. Finally, a database of FRP–stirrup composite-confined concrete column test results with different corner radii was established. The general calculation models were proposed, respectively, for the peak points, ultimate points and stress–strain models that are applicable to FRP-, stirrup- and FRP–stirrup-confined concrete columns with different cross-sectional shapes under axial compression.

Compression Behavior of Concrete Columns Strengthened by a Hybrid Bfrp/Hdpe Tube Coupled with a Crumb Rubber Concrete Cladding Layer

Compression Behavior of Concrete Columns Strengthened by a Hybrid Bfrp/Hdpe Tube Coupled with a Crumb Rubber Concrete Cladding Layer

Compressive behaviour of concrete column confined with basalt textile reinforced ECC

This paper presents experimental and numerical studies on the compressive behaviour of concrete columns strengthened with a composite reinforcement layer, which was combined by basalt fibre textile and Engineered Cementitious Composites (ECC). Concrete columns strengthened with textile reinforced ECC, textile reinforced mortar (TRM) and unreinforced were tested to investigate their compressive behaviour. The experimental results showed that the columns confined with textile reinforced ECC exhibited a better performance in strength and ductility than columns confined with TRM. A three-dimensional finite element model was developed to investigate the behaviour of concrete column strengthened with textile reinforced ECC, and the model was validated by comparing the results with those obtained from experiments. A parametric study was then conducted to investigate the effects of spacing and number of textile layers on the performance of the composite column. An analytical model on compressive resistance of columns with textile reinforced ECC was also developed with consideration of the spacing and number of textile layers.

Axial compressive stress–strain model for hybrid-reinforced concrete columns with FRP ties

The use of fibre-reinforced polymers (FRPs) as internal confining reinforcement in combination with longitudinal steel bars in concrete compression members provides significantly improved strength, ductility and durability. To date, only a few experimental studies have been carried out to establish the compressive behaviour of concrete columns longitudinally reinforced with steel bars and confined with FRP ties. This paper provides a confinement model with several expressions for predicting the axial stress–strain response of hybrid-reinforced (i.e. longitudinal steel bars combined with FRP ties) square concrete columns under axial compression loading. The model considers the influences of several test parameters, such as the configuration, size, volumetric ratio, spacing and type of ties (FRP pultruded bar ties and closed-type wound rectangular-section ties). The proposed model predicted well the peak and ultimate strength and strains compared with existing models. The overall accuracy of the model was also assessed against selected test stress–strain responses.

Experimental study on the axial compression behavior of columns confined by BFRP ties

Few studies have investigated concrete columns reinforced with basalt fiber-reinforced polymer (BFRP) ties. Due to its cost effectiveness, manufacturability, and good corrosion resistance, BFRP should be considered for use in concrete columns. This study experimentally investigated the axial compression behavior of concrete columns longitudinally reinforced with steel bars and transversely reinforced with BFRP ties. The test variables included the tie type, spacing, diameter, and configuration, the longitudinal bar type and the concrete strength. The test results indicated that the steel ties were better than the BFRP ties in enhancing the concrete strength and ultimate load, whereas the BFRP ties improved the post-peak ductility. A smaller tie spacing effectively improved the strength and ductility, and a larger BFRP tie diameter was more beneficial for improving ductility than load capacity. The combination of outer and inner rectangular BFRP ties was best for ductility improvement. At the peak load, the BFRP bars carried far less load than the steel bars; however, the BFRP or hybrid bars provided better ductility. Increasing the concrete strength grade increased the load capacity and decreased the ductility of the column.

Uniaxial Compressive Behavior of Concrete Columns Confined with Superelastic Shape Memory Alloy Wires.

Superelastic shape memory alloy (SMA) exhibits the ability to undergo large deformations before reverting back to its undeformed shape following the removal of the load. This unique property underlies its great potential in the seismic design and retrofitting of structure members. In this paper, superelastic SMA wires were utilized to confine concrete cylinders to enhance their axial compressive behavior. The axial carrying and deformation capacities of SMA-confined concrete cylinders are assessed by uniaxial compression testing on a total of eight SMA-confined concrete columns and one unconfined column. The influence of the amount of SMA and the prestrain level of SMA wires, as well as the reinforcing mode, on the axial carrying and deformation capacity of confined concrete columns were considered. The analysis focuses on the axial carrying capacity and deformation performance of concrete columns reinforced with superelastic SMA under different loading conditions. Based on the experimental data and analysis results, it is found that superelastic SMA wires can increase the axial loading capacity and enhance deformation performance of concrete columns. Under the same loading condition, the ultimate bearing capacity of SMA-confined concrete columns increases as the increasing of the amount of SMA wire. The results of this study verify the effectiveness of superelastic SMA in enhancing the loading capacity and deformation behavior of concrete cylinders.

Compressive behavior of circular and square concrete column externally confined by different types of basalt fiber–reinforced polymer

This article studies the compressive behavior of concrete columns confined by different basalt fiber–reinforced polymers. A total of 30 columns were divided into 10 groups according to section shapes (circular and square), basalt fiber–reinforced polymer types (unidirectional basalt fiber–reinforced polymer, bidirectional basalt fiber–reinforced polymer, and hybrid basalt fiber–reinforced polymer/carbon fiber–reinforced polymers), and number of layers (0, 1, and 2). The test results showed that the compressive strengths of confined specimens increased by 20%–71% for circular columns and by 23%–41% for square columns. Similarly, the ultimate strains improved by 49%–296% for circular specimens and by 45%–145% for square specimens. The two-layer basalt fiber–reinforced polymer jacket had the best confinement effect, whereas the confining effect of bidirectional basalt fiber–reinforced polymer wrapping was relatively lower than that of unidirectional basalt fiber–reinforced polymer wrapping. Moreover, both the strength and ultimate strain of confined concrete improved with increasing number of basalt fiber–reinforced polymer layers. Finite element numerical models were also developed and verified by experimental results, and then the stress distributions of basalt fiber–reinforced polymer jackets and cross-sectional concrete were presented. Based on the test results and experimental data from several existing studies, modified strength and ultimate strain models were further developed for basalt fiber–reinforced polymer-confined circular and square columns.

Experimental investigation of the performance of concrete columns strengthened with fiber reinforced concrete jacket

This paper presents an experimental study on the axial compressive behavior of concrete columns retrofitted and confined by fiber-reinforced concrete (FRC) jackets. Three different engineered cementitious composite (ECC) mixes containing high-strength polyethylene fibers at three fiber volume fractions of 0%, 1%, and 2%, and one ultra-high performance cementitious composite (UHP) mix at fiber volume fraction of 4%, were prepared to produce FRC jackets around the core concrete. Horizontal stirrups were used in the FRC jackets with three different horizontal reinforcement ratios to investigate the effect of the level of confinement and the interaction between the conventional reinforcement and fibers. The results show that specimens having no fiber or stirrup in their retrofitting jacket exhibit a brittle behavior and only those containing both stirrup and fiber provide a ductile behavior. It was also observed that the lateral strain of the jacket layer at a given axial strain increased with an increase in the fiber content, indicating an increased rate of dilation for the jacket concrete at a higher fiber volume fraction. It was also found that the best solution to enhance both ductility and strength of columns using FRC jacket is to include a minimum of both fiber content and reinforcement in the jacketing layer. The observations of this study reveal the great potential of the use of FRC jackets in retrofitting of structural members, especially columns in seismic regions.

Axial compressive behavior of concrete columns with grade 600 MPa reinforcing bars

An experimental study was performed to investigate the axial compressive behavior of concrete columns with Grade 600 MPa reinforcing bars. Nine large-scale concrete square columns were constructed and tested under pure axial loading. The effects of Grade 600 MPa transverse reinforcement with two different configurations (Type A and B) and amounts were evaluated. The behavior of columns was characterized by sudden spalling of concrete cover and ductility failure for well-confined columns, which was dominated by effective confinement index (keρshfyh/fc′). Columns confined by Grade 600 MPa transverse reinforcement exhibited the better performance in terms of strength, post-peak deformability, and toughness when compared with columns reinforced with conventional steel. The benefit of using Grade 600 MPa longitudinal bars on the axial load capacity of columns is limited, but it is beneficial to improve the post-peak deformability and toughness of columns with Type B configuration. A design expression is proposed for the amount of seismic confinement to ensure ductility behavior for columns, based on the effective confinement index.

Experimental study and theoretical analysis on axial compressive behavior of concrete columns reinforced with GFRP bars and PVA fibers

There have been some studies on the axial compressive behavior of concrete columns reinforced with fiber-reinforced polymer (FRP) bars. But most studies focused on normal concrete without fibers. In this paper, 10 concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars and polyvinyl alcohol (PVA) fibers were designed to investigate the influence of reinforcement type, longitudinal reinforcement ratio, spacing and size of GFRP ties on the axial compressive behavior of the specimens. Analytical and numerical studies were explored in this paper. The test results indicated that the concrete column reinforced with GFRP bars and PVA fibers (GFRP PVA-FRC column) and the concrete column reinforced with steel bars and PVA fibers (steel PVA-FRC column) had the similar failure processes and failure modes. The axial bearing capacity and brittleness of the GFRP PVA-FRC columns increased with the increasing longitudinal reinforcement ratio. When the volumetric ratio was constant, the confinement efficiency and ductility of the specimens using GFRP ties with smaller diameter and closer spacing were higher than that using GFRP ties with larger diameter and larger spacing. A new stress-strain constitutive model for PVA fiber reinforced concrete confined by GFRP bars was proposed. The numerical results showed that the concrete in the columns reinforced with GFRP longitudinal bars and GFRP ties could give full play to its strength. The conclusions could be references for the engineering application.

Compressive behaviour of concrete columns confined with steel-reinforced grout jackets

Abstract This paper investigates the compressive strength of concrete columns confined with a new jacketing system using high strength steel reinforced fabrics embedded in an inorganic matrix (SRG). A comprehensive experimental programme was conducted on 52 cylindrical columns with SRG jackets and 15 control specimens under monotonic uniaxial compression load. The test specimens were designed to investigate the influence of different design parameters including the density of the fabric (1, 1.57, 4.72 cords/cm), number of layers (1, 2), overlap length (24, 36 cm), bonding agent (4 different types of mortar) and the concrete strength (16–30 MPa). The test results highlight the efficiency of the proposed method, where one-layered and two-layered SRG jackets could increase the strength capacity of the unconfined specimens by up to 122% and 193%, respectively.

Effect of seawater exposure on compressive behavior of concrete columns reinforced longitudinally with glass fiber reinforced polymer bars

An experimental study was performed to investigate the effect of seawater exposure on the mechanical behavior of concrete columns reinforced longitudinally with glass fiber reinforced polymer (CCR-GFRP) bars. Numerous salt crystals emerged and slight exfoliation was observed after the surfaces of the columns were immersed in seawater for 120 days. The CCR-GFRP failed in either the axial compressive failure or split-crack failure mode. Furthermore, the probability of split-crack failure gradually increased with the duration of seawater exposure. In general, the carrying capacity of the CCR-GFRP initially increased and then decreased as the seawater exposure progressed. The strains of the surface concrete and inner glass fiber reinforced polymer bars continuously increased, but the strain of the glass fiber reinforced polymer bars and probability of the variability of the strain were less than those of the surface concrete. In addition, the bonding between the glass fiber reinforced polymer bars and concrete gradually decreased with increasing diameter of the glass fiber reinforced polymer bars. As the exposure period increased, the bonding between the glass fiber reinforced polymer bars of the same concrete columns weakened significantly.