Short Composite Columns Research Articles

Experimental investigation and numerical modelling of the seismic performance of reinforced concrete - engineered cementitious composite short columns

Four reinforced concrete - engineered cementitious composite (RC-ECC) short columns and one RC short column were subjected to quasi-static loading testing in this study. Digital image correlation (DIC) technology was adopted to observe the loading process. Thereby the influence of ECC replacement height and axial compression ratio on the seismic behavior of RC-ECC short columns was systematically studied. The test results indicate that all specimens had undergone flexural-shear failure dominated by shear failure. As the replacement height of ECC added, the number of horizontal cracks in the specimen enlarged, whereas the number and width of oblique cracks progressively diminished; The specimen's bearing ability changed less, the deformability and energy dissipation ability improved, and the shear strain and the proportion of shear deformation constantly dropped. Nevertheless, with the rising of ECC replacement height in a certain range, the improvement in seismic performance of the column decreased. As the axial compression ratio improved, the number of oblique cracks in the specimen reduced, the width of the main shear oblique crack enlarged, and the deformation capacity, energy dissipation capacity, and shear deformation proportion all exhibited a downward trend. Finally, based on the ABAQUS finite element platform, a numerical model of RC-ECC short columns was established and confirmed.

Mechanical Properties of Rolled-Steel Special-Shaped Short Composite Columns with Different Structural Forms Under Axial Compression

Mechanical Properties of Rolled-Steel Special-Shaped Short Composite Columns with Different Structural Forms Under Axial Compression

Experimental study on performance of reinforced concrete short columns repaired and strengthened with Basalt fiber ultra-high-performance concrete (BF-UHPC)

To explore the reinforcement effectiveness of basalt fiber UHPC repair materials on concrete structures, this study designed four types of wrapping materials for C40 concrete short columns (inner columns), and formed four types of composite short columns. Axial compression tests were conducted on these specimens to analyze the effects of wrapping material type, wrapping material thickness, and protective layer thickness on bearing capacity. Additionally, a model for axial compressive bearing capacity of short column specimens, based on the Mander model and relevant parameter modifications, was established. The results show that: (1) All designed short column specimens showed brittle failure in the experiment, and the brittle failure phenomenon during the experiment is like that of ordinary concrete short columns constrained by stirrups. (2) The type of wrapping material and the thickness of the wrapping layer are important factors affecting the axial compressive bearing capacity of the entire short column. (3) Adding an appropriate amount of basalt fiber and nano-silica significantly enhances the reinforcing and repairing capabilities of the repair material, thereby improving the load-bearing capacity of the repaired concrete columns. (4) Based on the Mander model and the correction of correlation coefficients, a model for axial compressive bearing capacity of short column specimens was established.

Experimental study on the fully encased composite short columns made with high-strength fibre-reinforced concrete

Experimental study on the fully encased composite short columns made with high-strength fibre-reinforced concrete

Axial Compression Behavior of Elliptical Concrete-Filled Steel Tube Composite Short Columns with Encased Steel Considering Spherical-Cap Gap

This study explored the axial compression behavior of elliptical concrete-filled steel tubes with encased steel considering spherical-cap gap (GSECFST) composite short columns. We designed 25 composite column specimens by varying the steel tube yield strength (fty), steel skeleton yield strength (fsy), concrete cubic compression strength (fcu), steel tube thickness (t), steel skeleton sectional area (As), the long and short half-axis ratio (a/b), the gap ratio (Xsg), and the slenderness ratio (λ). Based on the nonlinear constitutive models of the materials and the nonlinear contact effect among materials, the ABAQUS 6.20 finite element software established the refined finite element models of these composite short columns. Also, the rationality of the finite element modeling with a spherical-cap gap was verified by comparing it with the existing experimental results. The influence regularity of various parameters on the load (N)-displacement (Δ) curves, bearing capacity, initial stiffness, and ductility of the composite short columns was obtained. In addition, the failure modes, N-Δ process, sectional strain distribution, and gap feature index of the constraint partition model for GSECFST axial compression short columns were revealed. The results showed a weakened interaction between the elliptical steel tube and concrete. Also, the axial compression bearing capacity, initial stiffness, and core concrete ductility were reduced because of the spherical-cap gap. As fty, fsy, fc, and Asy increased, the axial bearing capacity, initial stiffness, and ductility of GSECFST composite short columns improved significantly but decreased with increasing of a/b, Xsg, and λ. When the gap ratio of the spherical crown was less than 4%, the outer steel tubes in the mid-span area of the GSECFST composite short columns buckled in the direction of the elliptical short axis under axial compression, and the concrete expanded outward and crushed. The failures were similar to those of the specimens without the spherical-cap gap. Based on the sectional constraint partition model, we propose the calculation formula of axial compression bearing capacity for GSECFST composite short columns. Consequently, this study is a reference for the elastic-plastic analysis of frame systems with similar composite columns.

Axial compressive behavior of circular composite columns with external confinement

With the advance of externally confined composite columns, a generic model that can predict the ultimate axial compressive strength of both circular concrete-filled steel tube (CFST) and concrete-filled double skin steel tubes (CFDST) short columns with external confinement is very attractive. For this purpose, a rich experiment database of composite columns is assembled, guides to build up this database are outlined, and its limitations are also summarized. Based on some fundamental considerations, a simple formula for estimating ultimate axial compression of circular composite short columns is proposed first. The hoop and longitudinal stresses of outer and inner (if any) steel tubes are then determined by the stress analysis, from which the assumption frequently used in previous studies that the sandwiched concrete in a CFDST column is under uniform confinement is demonstrated to be unreasonable. Besides, the additional external confining pressure provided by external confinement in the form of steel spirals, rings, jackets, or tie bars is thoroughly investigated. Further, to comprehend the triaxial strength of infilled concrete in both CFST and CFDST columns, a novel concept of equivalent confining stress that can reflect both uniform and non-uniform confinement effects is defined, with which a modified Power-law failure criterion is established. Model validations illustrate that this generic model can reasonably estimate the strength of externally confined CFST and CFDST columns. Although it currently slightly underestimates the strength of ring-enhanced CFDST columns, this limitation can be easily overcome by recalibrating some coefficients without rebuilding the proposed framework.

Experimental and Numerical Investigations of Laced Built-Up Lightweight Concrete Encased Columns Subjected to Cyclic Axial Load

The steel-concrete composite column comprises a steel core and surrounding concrete. The purpose of the system is to provide analysis and design techniques for a newly invented class of laced steel-concrete composite short columns for cyclic axial loads. To minimize the increasing density issues associated with nominal strength concrete and in consideration of the depletion of natural resources required to produce concrete, factory-obtained lightweight sintered fly ash aggregates with and without basalt fiber are employed. The normal-weight concrete containing basalt fiber is shown to be more ductile than any other column. The axial deformation of columns LNA and LSA at failure was found to be 3.5 mm, whereas columns LNAF and LSAF reached an axial shortening of 4.5 mm at failure. The column LSAF was found to have 5.3% more energy absorption than the LSA and 11.5% less than the column LNAF. It was observed that the rigidity of these fabricated components had been enhanced. It was found that the section configuration with a lacing system had improved confinement effects and ductility. Comparing the finite element analysis to the experimental data revealed a strong connection with numerical modeling, with a variance of around 8.77%.

Experimental studies on the axial compression behavior of hollow sandwich concrete GFRP-steel tube composite short columns

This paper explores the mechanical mechanisms and properties of hollow-sandwich concrete GFRP–steel tube composite short columns under axial compression to promote their application in the practical engineering of bridge piers under high-salinity and high-humidity corrosion environments. The force action, stress state and mechanical calculation model of composite short columns are important manifestations reflecting the mechanical mechanism, and the mechanical properties are measured by failure characteristics, bearing capacity, initial stiffness, ductility coefficient, energy dissipation value, damage coefficient and load–displacement curve. In this paper, an axial compression test of 15 composite short columns was designed and carried out with the parameters of section form, GFRP tube thickness, concrete strength, hollow ratio and steel tube thickness. The results showed that the specimens exhibited typical local pressure or shear failure, which is characterized by tearing of the GFRP tube fiber. The built-in steel tube can improve the ultimate bearing capacity of the specimen, and the ductility and axial compression energy dissipation of the double-tube concrete short column (DTCC) is basically consistent with hollow sandwich concrete GFRP-steel tube composite short columns (DSTCs). With a reasonable hollow ratio, the DSTCs can meet the same mechanical properties and deformation performance requirements as the DTCC. Compared with concrete strength and steel tube thickness, the influence of GFRP tube thickness and hollow ratio on the ultimate bearing capacity of specimens is more obvious. Under the action of axial compression, the sandwich concrete is changed from a unidirectional compression state to a complex three-dimensional compression-confined concrete. The GFRP tube and steel tube change from unidirectional compression to a bidirectional stress state. Based on the plastic theory analysis, considering the influence of uneven distribution of the concrete stress state along the radial direction, the calculation model of axial compression bearing capacity of hollow sandwich concrete GFRP-steel tube composite short columns is derived. The calculation results are in good agreement with the experimental results.

Unified compressive strength model for axially loaded circular composite short columns

Composite columns are widely used in modern structures owing primarily to their excellent structural performance, but they usually have very different ultimate axial compressive strength prediction models, which may lead to confusion for researchers and engineering designers. In addition, given the similarity of their mechanical mechanisms, there may be a generic prediction model for these columns. Hence, the authors aim to provide a simple and effective unified ultimate compression prediction model for axially loaded circular composite short columns. A rich experimental database is firstly established. Then the force analysis of a typical concrete-filled double-skin steel tubes (CFDST) column is illustrated, and it can be easily extended to other types of composite columns. Based on the above force analysis, the stress state of each component of the column can be determined via different sections and loading concepts. Contributions of the inner steel tube to the load-bearing capacity are further clarified, and the passively confined compressive strength of the concrete core is also investigated on the basis of the proposed equivalent confining stress. Subsequently, the calculation flow of the ultimate compression strength is briefly demonstrated. Finally, the ultimate compression prediction model is evaluated by the established test database, and good consistency can be observed for circular composite short columns with a widely varied parameter.

Compressive constitutive models of bamboo and fiber-reinforced phosphogypsum and axial compression properties of composite short columns

Bamboo is an ideal building material with green, fast growing and good mechanical properties. Phosphogypsum is a kind of solid waste residue with low resource utilization and has been used as building material. Finite element analysis is an important means of structural research. In this paper, the stress-strain constitutive models of bamboo and phosphogypsum were explored based on material tests, and axial compression tests of three bamboo-phosphogypsum composite short columns were carried out. Based on the constitutive models, the simulation and test results of composite short columns were compared by finite element analysis. The results show that the finite element analysis has high accuracy. The finite element analysis of 32 models was carried out considering the influence of bamboo tube wall thickness, bamboo tube density, phosphogypsum fiber ratio, bamboo tube longitudinal reinforcement and stirrup. The results show that the bearing capacity of composite short columns increases with the increase of bamboo tube wall thickness, bamboo tube density, phosphogypsum fiber ratio, longitudinal reinforcement diameter and density, and stirrup diameter and density. The thickness of bamboo tube wall and density of bamboo tube have a significant effect on the bearing capacity of composite short columns. A method for calculating the bearing capacity of composite short columns was presented, which has high accuracy. • The constitutive models of bamboo and phosphogypsum were proposed. • A kind of bamboo-phosphogypsum composite short column was proposed. • A theoretical calculation method for the bearing capacity of bamboo-phosphogypsum composite short columns was established.

Behavior of eccentrically loaded UHPC filled circular steel tubular short columns

This paper presents experimental results of twelve eccentrically loaded short composite columns made by filling circular steel tubes with ultra-high performance concrete (UHPC) cured under room temperature. Using these test data as benchmarks, finite element models are developed and used to perform parametric studies to determine how the capacities of these columns are affected by load eccentricity and tube diameter-to-thickness ratio. In addition, a relationship between the balanced eccentricity ratio and the confinement coefficient is established. The results of the present study have shown that: (1) failure of these columns is characterized by yielding of the steel tubes, followed immediately by failure of the core concrete; (2) a decrease in diameter-to-thickness ratio increases the peak load and improves the column's post-peak behavior; (3) an increase in the load eccentricity ratio results in a reduction of the load capacity, ductility and stiffness of the column; (4) the compressive strain in the steel tube develops more rapidly due to second-order effect, and the assumption that plane sections remain plane no longer applies when the applied load reaches 80% of the peak load. By comparing the axial force – Bending moment (Nu-Mu) interaction diagrams generated in the present study with existing codes, it is found that the code equations are mostly conservative. A set of trilinear Nu-Mu interaction equations that can produce more accurate results is therefore proposed

Experimental Study on Axial Compression Performance of 7A04 High Strength Aluminum Alloy Circular Tube Concrete Short Column

The application of tube-filled concrete composite columns is becoming more and more popular. The traditional tube-filled column is easy to rust and expensive to maintain, which leads to the practical need of replacing high-strength aluminum alloy. 7A04 aluminum alloy has high strength and strong corrosion resistance, which is more in line with the material requirements of modern building structures. In view of this, four groups of 7A04 aluminum alloy tube concrete short columns were tested under axial compression, and the corresponding ABAQUS finite element simulation was established. The influence of tube thickness and concrete strength grade on compressive strength, ductility, transverse deformation coefficient, and improvement coefficient of strong concrete strength of composite column is considered in this paper. The results show that the failure mode of composite short columns is central uplift or shear failure. The tube thickness of high-strength aluminum tube has a great influence on the strength of specimens, and the ductility of composite columns decreases with the decrease of the collar coefficient. The finite element model can well reflect the development trend of the load-strain curve, and the formula of composite column bearing capacity proposed by regression analysis can well predict the strength of 7A04 aluminum alloy tubular concrete short column. The research results have a certain reference significance for the structural design of high strength aluminum concrete-filled columns.

Experimental behavior of circular composite columns with different weld arrangements

Eighteen (18) circular short composite columns including 9 concrete-filled steel columns and 9 concrete-filled stainless steel columns, were experimentally studied in this paper. All composite columns have the same dimensions: D= 160 mm, H= 300 mm and t= 2 mm. The objective of this study is to shed light on the effect of the number and arrangement of lateral and longitudinal welds on the resistance and behavior of concrete-filled composite columns. Based on the results obtained, it was confirmed that weld joints have slight effect on the bearing capacity and instability modes of the studied composite columns. Lateral and longitudinal welds were very successful in conveying compression and bending efforts. The experimentally measured load-bearing capacities of the composite columns were compared to those predicted by Eurocode 4, AISC 360–16 and the equation proposed by Giakoumelis and Lam. All the results predicted by the AISC 360–16 code showed a good concordance with the experimental test results. However, the predictions calculated by the EC4 and the equation proposed by Giakoumelis and Lam were not conservative. This investigation shows that the use of lateral and longitudinal welds in composite columns applications would result in a reliable and economical design. This encourages designers to build their confidence in the use of this type of waste metal plates as structural components of locally produced materials.

The Investigation on Mechanical Performances of High-Strength Steel Reinforced Concrete Composite Short Columns under Axial Load.

At present, the existing standards (AISC360-16, EN1994-1-1:2004, and JGJ138-2016) lack relevant provisions for steel-reinforced concrete (SRC) composite columns with high-strength steel. To investigate the axial compressive mechanical performance of short high-strength steel-reinforced concrete (HSSRC) columns, the axial load test was conducted on 12 short composite columns with high-strength steel and ordinary steel. The influences of steel strength, steel ratio, and the section form of steel on the failure modes, bearing capacity, and ductility of the specimens were studied. Afterward, the experimental data were compared with the existing calculation results. The results show: compared with the specimens with Q235 steel, the bearing capacity of the specimens with Q460 steel increases by 7.8–15.3%, the bearing capacity of the specimens with Q690 steel increases by 13.2–24.1%, but the ductility coefficient increases by 15.2–202.4%; with the increase of steel ratio, the bearing capacity and ductility of specimens are significantly improved. A change of the steel cross-section could influence the ductility of SRC columns more than their bearing capacity. Moreover, the calculation results show that present standards could not predict the bearing capacity of HSSRC columns. Therefore, a modified method for determining the effective strength of steel equipped in HSSRC columns was proposed. The results of the ABAQUS simulation also showed that the addition of steel fibers could significantly improve the bearing capacity of Q690 HSSRC columns. The research results provide a reference for engineering practices.

Effect of splitting bond on shear response of reinforced engineered cementitious composite short columns under cyclic loading

The effect of splitting bond on shear response of reinforced engineered cementitious composites (RECC) short columns under cyclic loading is experimentally investigated in this paper. Nine RECC short columns were designed to test the effect of axial load ratio, stirrup spacing and shear span-to-depth ratio on their cyclic response, and one reinforced concrete (RC) short column was prepared for comparison. The test results show that the RC short column failed in shear-splitting bond failure (shear accompanied by splitting bond) with poor plastic deformation and low energy dissipation. Splitting bond failure was effectively delayed in RECC short columns due to the high tensile strength and ductility of ECC, the RECC short columns failed in shear-splitting bond failure with ductile characteristics and thus exhibited improved cyclic response. In particular, the RECC short column corresponding to the control RC short column gained a 54.5% and a 60.7% improvement in ultimate drift ratio and cumulative energy dissipation, respectively. Additionally, a series of formulas based on truss-arch model was proposed to predict the shear strength of RECC short columns controlled by splitting bond, and the proposed model gives reasonable calculated results compared with the test results.

Study on Axial Compression Performance of GFRP Tube Reactive Power Concrete Composite Short Columns with Encased Steel

In order to study the axial compression performance of the GFRP tube reactive power concrete composite short column with encased steel, a finite element model of the composite short column was established. The constitutive models of steel, RPC and GFRP were selected. The element selection and contact method of each component were explained. The boundary condition and mesh division of the composite column were determined. Based on this, finite element verification analysis of 6 specimens was performed by ABAQUS. The load-displacement curves and the axial compression bearing capacity were obtained. By comparing with the test, the reasonability of the constitutive model and the finite element model of this kind of column is verified.

Axial compression behavior of concrete-encased cellular steel columns

This paper presents an axial compression behavior of bare and concrete-encased cellular steel (CECS) short columns. Three cellular steel configurations with different hole diameters and spacings were fabricated from the parent wide-flange hot-rolled steel shape. Eleven CECS columns using the cellular steel and four concrete-encased steel (CES) columns using the parent steel were tested to investigate the influence of the cellular steel configuration and the spacing between the closed stirrups. The test results of bare cellular steel columns showed that the failure was due to local buckling at the steel flanges and web at the hole section. The bare cellular columns exhibited the load-deformation relationship with less hardening behavior than the parent steel column. The proportional limit loads, yield loads, and maximum loads of all cellular steel columns were less than the parent column. The test results of composite columns showed that the CECS columns exhibited the failure mode, load-deformation relationship, and load-strain relationship similar to the CES parent columns. The weakening effect due to the circular openings was minimized by the concrete encasement. The compressive strength of CECS and CES columns increased as spacing of the closed stirrups decreased. A modified squash load equation is recommended for both CECS and CES composite short columns made with low-strength concrete, small amount of longitudinal rebars, and maximum stirrup spacing limit based on the ANSI/AISC360–16 specification.

How to determine a value of the bifurcation shortening of real thin-walled laminated columns subjected to uniform compression?

In the present paper, a methodology for determination of a value of the bifurcation shortening and the corresponding bifurcation load of the real thin-walled laminated column under compression with initial imperfections, using an axial shortening versus squared deflection amplitude plot, is presented. A plate model of the column has been assumed. It has been shown that the post-buckling state is described with a linear relationship on this plot, whereas a value of the bifurcation shortening corresponds to a free term of the straight line approximating the post-buckling state on the plot and is proportional to the bifurcation load.Detailed calculations have been conducted for short composite angle columns under uniform compression. The eigenvalue problem and the non-linear post-buckling problem have been solved with the semi-analytical method (SAM) based on Byskov-Hutchinson’s method and the finite element method (FEM). The bifurcation shortening and the corresponding bifurcation load have been determined. An effect of the imperfection amplitude on the post-buckling behaviour of laminated thin-walled angle columns has been analysed. General configurations of laminate plies have been selected. All columns have been simply supported at both ends. A very good agreement between the results attained with both the methods for solving the non-linear problem has been obtained.

Plastic stress distribution method for predicting interaction strength of steel-concrete composite cross sections

Steel-concrete composite columns are efficient structural members that possess significant strength, stiffness, and ductility. Accurate methods of assessing the strength of these members are necessary to realize their benefits. Several design codes rely on the plastic stress distribution method for computing the cross-sectional strength of composite columns subjected to axial compression and flexural bending. However, there has been limited validation of this method over the wide range of material properties, cross-sectional geometries, and loading conditions to which it is permitted to be applied. This paper presents a study of the behavior of short composite columns and methods of evaluating their strength. The use of the plastic stress distribution method and the strain compatibility method to evaluate the strength of composite columns is validated against detailed fiber cross section analyses and published experimental data. The results of this study indicate that the plastic stress distribution method can yield significantly unconservative strength predictions, especially for encased composite members with high steel yield strengths and high steel ratios. Motivated by these results, a simple modification factor which can be applied to the results of the plastic stress distribution method to achieve greater accuracy was derived. This modification factor is suitable for use in design practice and enables better predictions of the strength of short composite columns.

Partially encased composite columns using fiber reinforced concrete: experimental study

This paper addresses the results of an experimental study involving 10 partially encased composite columns under concentric and eccentric compressive loads. Parameters such as slenderness ratio, ordinary reinforced concrete and fiber reinforced concrete, load eccentricity and bending axis were investigated. The specimens were tested to investigate the effects of replacing the ordinary reinforced concrete by fiber reinforced concrete on the load capacity and behavior of short and slender composite columns. Various characteristics such as load capacity, axial strains behavior, stiffness, strains on steel and concrete and failure mode are discussed. The main conclusions that may be drawn from all the test results is that the behavior and ultimate load are rather sensitive to the slenderness of the columns and to the eccentricity of loading, specially the bending axis. Experimental results also indicate that replacing the ordinary reinforced concrete by steel fiber reinforced concrete has no considerable effects on the load capacity and behavior of the short and slender columns and the proposed replacement presented very good results.