Strength Of Composite Columns Research Articles

VARIABLE STIFFNESS REDUCTION FACTOR FOR STABILITY DESIGN OF STEEL‐CONCRETE COMPOSITE COLUMNS

AbstractIn United States practice, the strength of composite columns is assessed with available strengths that are computed considering member length effects. This approach has advantages; however, developing axial compression‐bending moment interaction diagrams that account for member length effects is not a straightforward task. Current methods result in unconservative error for highly slender members with large bending moments. While it is theoretically possible to develop more accurate interaction diagrams, a simpler approach, and one which more directly addresses the cause of the unconservative error, is to improve the accuracy of the stiffness used in the elastic analyses to determine required strengths. In this work, new recommendations are developed for this stiffness for steel‐concrete composite columns. The recommended stiffness is a function of required axial compression and bending moment, which increases accuracy and enables improved available strength calculations, resulting in more efficient designs.

Behavior and Strength of Composite Columns under the Impact of Uniaxial Compression Loading

The Concrete Filled Steel Tube Column (CFST) is classified as a composite structural element. This type of column was adopted as the main loaded member in many buildings due to its excellent mechanical properties. CFST columns have high strength and ductility behavior, and they can sustain heavy loads with high performance. These led to their adoption in many countries. In the current study, the behavior and strength of CFST columns under the effect of axial compression load with parameters such as the diameter to thickness ratio and the height to diameter ratio were investigated. Strength carrying capacity and axial and lateral deformations with axial and lateral strains were explored. The test results showed that smaller heights within the same material gave higher strength capacity. The stiffness of the CFST is more than concrete and hollow steel section specimens' due to its capability of high strength capacity with low displacement. Also, the composite action of CFST gave more stiffness.

Finite element analysis of behavior and ultimate strength of composite column

Abstract Composite sections are found to be a novel technique in modern day scenario of construction. This stands tall than the ordinary and conventional type of constructions. Columns as a structural element play a vital role in structural frame. This research comments on the behavior of composite columns. The main objective of this study is to analyze the behavior of steel-encased concrete composite columns as experimentally under axial compression and the mode of failure under ultimate failure and yield point. The steel-concrete composite system combines the formability and rigidity of reinforced concrete with the ductility and strength of structural steel to meet the demand for earthquake-resistant constructions. Three specimens were chosen for this study: one was a composite column, the other two were ordinary RC columns and structural steel columns. The raw materials' natural properties are assessed. As a result, material testing for cement, fine aggregate, and coarse aggregate was completed, as well as a concrete mix design. A comparative analysis of the local and post-local buckling behavior of different composite sections has been studied and the column sections have been designed according to Eurocode 4 (ENV 1994) to determine the plastic resistance of the section. These three specimens underwent compression test and the results are tabulated and compared. The corrosion resistance and fireproof nature (resistance to fire at higher temperatures) that are transmitted into the member are related to the steel being encased within the concrete. These are the two major drawbacks of any steel construction combined with an earthquake-resistant structure. Rather than a traditional steel construction, earthquake structures benefit from this type of load handling capabilities. The portion can be used before it completely collapses if proper design factors are taken into account.

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.

Use of the Gene-Expression Programming Equation and FEM for the High-Strength CFST Columns

The ultimate strength of composite columns is a significant factor for engineers and, therefore, finding a trustworthy and quick method to predict it with a good accuracy is very important. In the previous studies, the gene expression programming (GEP), as a new methodology, was trained and tested for a number of concrete-filled steel tube (CFST) samples and a GEP-based equation was proposed to estimate the ultimate bearing capacity of the CFST columns. In this study, however, the equation is considered to be validated for its results, and to ensure it is clearly capable of predicting the ultimate bearing capacity of the columns with high-strength concrete. Therefore, 32 samples with high-strength concrete were considered and they were modelled using the finite element method (FEM). The ultimate bearing capacity was obtained by FEM, and was compared with the results achieved from the GEP equation, and both were compared to the respective experimental results. It was evident from the results that the majority of values obtained from GEP were closer to the real experimental data than those obtained from FEM. This demonstrates the accuracy of the predictive equation obtained from GEP for these types of CFST column.

Bond Strength of Concrete-Filled Hollow Section with Modified Fibrous Foamed Concrete

The concrete-filled section of columns has been widely in construction used due to its structural elements. As a result, the usage of composite columns has recently increased all over the world. However, using foamed concrete alone does not result in much improvements in strength. Therefore, this paper examines the use of foamed concrete containing fibre to improve the strength of composite columns. Specifically, this study aims to determine the bond strength of concrete-filled hollow section (CFHS) with modified fibrous foamed concrete. Two types of fibre are used in this work, namely, steel fibre and polypropylene fibre, with rice husk ash (RHA) as a sand replacement to improve the compressive strength of foamed concrete. The CFHS with modified fibrous foamed concrete is tested by using the push-out method, and the results show that CFHS with steel fibre has a highest bond strength.

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.

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.

Compressive strengths of concrete-filled double-skin (circular hollow section outer and square hollow section inner) aluminium tubular sections

Experimental and numerical investigations of concrete-filled double-skin aluminium stub column with a circular hollow section as the outer skin and a square hollow section as the inner skin are presented in this article. A test program was carried out to study the influences of aluminium tube geometric dimensions and concrete strength on structural performance and strength of composite columns. A series of composite columns was tested on outer circular hollow section tubes and inner square hollow section tubes; the spaces between them had been filled with concrete of different nominal cylinder strengths of 40, 70 and 100 MPa. The tubes were fabricated by extrusion using 6061T6 heat-treated aluminium alloy having a nominal 0.2% proof stress of 240 MPa. A non-linear finite element model was developed and verified against experimental results. The test and numerical results were compared with the design strengths to evaluate the applicability of the design rules in the American specifications for aluminium and concrete structures. In addition, the proposed design equations, developed by the authors for concrete-filled double-skin aluminium tubular stub columns with circular hollow section as both outer and inner skins, were used to calculate the design strengths and compared with the experimental and numerical results obtained in this study. The proposed design equations also predicted the ultimate strengths of the concrete-filled double-skin aluminium tubular stub columns accurately with circular hollow section as the outer skin and square hollow section as the inner skin.

Experimental investigation of concrete-filled single-skin and double-skin steel oval hollow section stub columns

Both concrete-filled single-skin and double-skin steel tubular stub columns were investigated experimentally in this study. The skin of the composite columns was constructed using steel oval hollow section (OHS) tubes. A series of tests was performed to investigate the effects of the geometric dimension of steel OHS tube and concrete strength on the behaviour and strength of composite columns. The overall width-to-thickness ratio of the OHS tube sections ranged from 15.8 to 62.6. The structural performance of the composite columns was investigated using different nominal concrete cylinder strengths of 40, 70 and 100 MPa. The composite column lengths were chosen so that the length-to-width ratio generally remained at a constant value of 3 to prevent overall column buckling. The concrete-filled OHS tube specimens were subjected to uniform axial compression. The test strengths, load-axial shortening relationship and failure modes of the composite columns were presented in this paper. The test strengths were compared with the design strengths calculated using the American Specification and European Code for composite steel and concrete structures. It was shown that the design strengths do not agree well with the experimental results.

EXPERIMENTAL AND COMPUTATIONAL STUDY OF CONCRET FILL ALUMINUM TUBULAR COLUMN UNDER AXIAL LOADS

This work deals with an experimental and computational study was carried out on the structural behavior of circular concrete filled aluminum tubular columns subjected to increasing axial load. Twenty four specimens were tested to investigate the effect of diameter, D/t ratio and slenderness ratio of a aluminum tube on the load carrying capacity of the concrete filled tubular columns. Diameter to wall thickness ratio between 23.3 ≤ D/t ≤ 47.8, and the length to tube diameter ratio of 3 ≤ L/D ≤ 10 was investigated. The structural performance of the concrete-filled aluminum tube columns (CFTa) was investigated using constant concrete cylinder strengths of 24.2 MPa.The main purpose of the computational study aimed to investigate the potential of using fuzzy inference system (FIS) to predict the strength of the composite columns. Fuzzy inference system (FIS) model has been provided to be very effective in predicting the ultimate strength of aluminum-concrete composite columns. The average values of ratios of experimental to predicted ultimate loads are 1.001 forthe Sugeno FIS model. The circular hollow section tubes were fabricated by extrusion using 6061-T6 heat-treated aluminum alloy

The Evaluation of the Axial Strength of Composite Column with HSA800 Grade Steel

건축구조기준에 따라 HSA800 강재의 합성기둥 적용시에는 실험 또는 해석적 방법을 통하여 적용의 타당성을 검증해야 한다. 이에 본 연구에서는 합성기둥으로 주로 사용되는 H형강 매입형, 각형강관 및 원형강관 충전형 합성기둥 단면을 대상으로 HSA800 강재를 적용한 단주압축실험을 실시하고, 이를 통하여 축방향 내력 및 건축구조기준의 합성기둥 설계압축강도 설계식 적용의 타당성을 평가하였다. 실험결과 매입형 합성기둥의 경우 HSA800 강재의 설계기준항복강도를 저감없이 사용하기 위해서는 건축구조기준의 설계압축강도 산정식의 조정이 필요한 것으로 나타났으며, 이를 위해 띠철근 간격 조정 및 콘크리트의 유효단면적 사용을 제안하였다. 충전형 합성기둥의 경우에는 각형, 원형충전강관 기둥 모두 별도의 강도 저감이나 설계압축강도 산정식의 조정 없이 사용이 가능할 것으로 판단된다. According to the Korean Building Code (KBC), the validity of the application of 800MPa grade steel(HSA800) to composite column should be verified by experimental or analytical method. Thus, stub column tests for encased and filled composite members with HSA800 steel were conducted, and axial strength and the validity of design compressive strength equations in KBC were evaluated. The test results show that the equation of the compressive strength of encased composite column member in KBC should be modified in order to use HSA800 steel without any reduction of specified minimum yield strength. For this purpose, it is suggested that the interval of hoop should be narrowed and the effective concrete area should be used. The equation of the compressive strength of filled composite column member in KBC is applicable to filled composite column with HSA800 steel without any modification.

Nonlinear behaviour of eccentrically loaded FR concrete-filled stainless steel tubular columns

This paper investigates the nonlinear behaviour of eccentrically loaded fibre reinforced (FR) concrete-filled stainless steel tubular composite columns. A nonlinear 3-D finite element model for the axially loaded composite columns, recently reported by the author, was extended to study the structural performance of the eccentrically loaded composite columns. The columns were pin-ended subjected to an eccentric load acting along one axis. The model accounted for the inelastic behaviour of the composite column components, effect of FR concrete confinement and interface between the stainless steel section and concrete. The measured initial local and overall geometric imperfections were carefully incorporated in the model. The finite element model has been validated against tests previously reported by the author. Furthermore, the variables that influence the eccentrically loaded composite column behaviour and strength comprising different eccentricities, different column slenderness and different concrete strengths were investigated in an extensive parametric study comprising 72 columns. The composite column strengths and moment resistances predicted from the finite element analysis were compared with the design composite column strengths and moment resistances calculated using the Eurocode 4. The study has shown that finite element modelling could effectively assess the accuracy of the design rules in current codes of practice.

Structural design of steel fibre reinforced concrete in-filled steel circular columns

This paper presents the behavior and design of axially loaded normal and steel fiber reinforced concrete in-filled steel tube (SFRCFT) columns, to examine the contribution of steel fibers on the compressive strength of the composite columns. Non-linear finite element analysis model (FEA) using ANSYS software has been developed and used in the analysis. The confinement effect provided by the steel tube is considered in the analysis. Comparisons of the analytical model results, along with other available experimental outputs from literature have been done to verify the structural model. The compressive strength and stiffness of SFRC composite columns were discussed, and the interpretation of the FEA model results has indicated that, the use of SFRC as infill material has a considerable effect on the strength and stiffness of the composite column. The analytical model results were compared with the existing design methods of composite columns - (EC4, AISC/LRFD and the Egyptian code of Practice for Steel Construction, ECPSC/LRFD). The comparison indicated that, the results of the FEA model were evaluated to an acceptable limit of accuracy. The code design equations were modified to introduce the steel fiber effect and compared with the results of the FEA model for verification.

Behavior of Eccentrically Loaded Plain and Steel Fiber Reinforced Concrete Filled Steel Box Columns

The present study investigates the behavior of steel fiber reinforced concrete filled steel box columns (SFRCFSBC) targeting to enhance their strength. A nonlinear finite element model using ANSYS program has been developed to investigate the structural behavior of the inspected columns. The results obtained from that model has been compared with those calculated using Euro code (EC4), AISC/LRFD (2005) and the Egyptian Code of Practice for Steel Construction (ECPSC/LRFD 2007). The comparison indicated that the results of the model have been evaluated to an acceptable limit of accuracy. A parametric study was carried out to investigate the effect of wall thickness, column slenderness and percentage of steel fiber in concrete on the ultimate strength of composite columns. Confinement of the concrete core provided by the steel case was also investigated. It can be concluded from the results that a considerable increase in compressive and flexural strength may be gained by increasing the steel fiber percentage up to 4%. The highest rate of increase in strength for long columns was about 20% by using steel fiber percentage between 0.5% and 1.0%, while for short and medium columns was about 10% by using steel fiber percentage between 1% and 2%.

Numerical modelling of fibre reinforced concrete-filled stainless steel tubular columns

The nonlinear behaviour of fibre reinforced (FR) concrete-filled stainless steel tubular columns is discussed in this paper. A nonlinear 3-D finite element model was developed for the analysis of the composite columns. The pin-ended axially loaded composite columns had different lengths, which varied from stub to long columns. The nonlinear material properties of the composite column’s components comprising stainless steel tube and FR concrete were incorporated in the model. The effect of FR concrete confinement and interface between the stainless steel tube and FR concrete infill was also considered allowing the bond behaviour to be modelled. In addition, the measured initial overall (out-of-straightness) geometric imperfection was carefully incorporated in the model. The finite element model has been validated against tests recently conducted by the author on FR concrete-filled stainless steel tubular columns. The composite column strengths, load–axial strain relationships and failure modes were predicted from the finite element analysis and compared well against that measured experimentally. Furthermore, the variables that influence the composite column behaviour and strength comprising different lengths, external diameter-to-plate thickness (D/t) ratios and FR concrete strengths were investigated in a parametric study. The parametric study has shown that the increase in column strengths owing to the increase in concrete strength is more significant for the columns having L/D ratios less than 6 as well as for the columns having D/t ratios less than 50. The composite column strengths obtained from the finite element analysis were compared with the design strengths calculated using Eurocode 4 for composite columns. It is shown that the EC4, in most cases, accurately predicted the design strength for axially loaded FR concrete filled stainless steel tubular columns.

Ultra-High Strength Concrete Filled Composite Columns for Multi-Storey Building Construction

A test programme was carried out to investigate the performance of 27 axially loaded column specimens, including 18 steel tubes infilled with ultra-high strength concrete ( UHSC) of compressive strength close to 200 MPa, 4 steel tubes infilled with normal strength concrete ( NSC) and 5 hollow steel tubes. Steel fibres were added into the UHSC to study their effect in enhancing the ductility and strength. Concrete filled double-tube columns were also investigated for potential application in multi-storey and high-rise constructions. Test results showed that UHSC filled tubular columns achieved ultra-high load-carrying capacities, but they could become brittle after the maximum load was attained. In addition, the ductility and strength of composite columns infilled with UHSC was improved by applying load only on the concrete core, adding steel fibres into the concrete core or increasing the steel contribution ratio. Comparison of test results with Eurocode 4's predictions indicates that the Eurocode 4 method could be safely extended to predict the compressive resistance of UHSC filled composite stub columns. On average, Eurocode 4 approach underestimated the resistance by 14.6% if the confinement effect was not considered and by 3.5% if the confinement effect was considered for all the specimens involving UHSC. However, to ensure sufficient ductility, it is recommended that a minimum steel contribution ratio of 0.30 or 1% steel fibres should be used. Furthermore, strength enhancement due to confinement effect should be ignored in estimating the ultimate strength of concrete filled composite columns with Class 3 steel sections.

Experimental Study on Compressive Bearing Capacity of High Strength Concrete-Filled Steel Tube Composite Columns

To study axial compressive strength of high strength concrete-filled steel tube composite columns, tests of 18 specimens were carried out. Parameters of the specimens were the confinement index of concrete-filled steel tube, the cubic strength and the stirrup characteristic value of concrete outer of steel tube. Test results show that the concrete-filled steel tube and the reinforced concrete deformed simultaneously in the axial direction before and at the peak value of axial compressive force; after failure of the reinforced concrete, the concrete-filled steel tube can still bear the axial load and deformation; the main influential factors of axial compressive capacity are confinement index, the cubic strength and the stirrup characteristic value of concrete outer of steel tube. The accuracy of the formula of axial compressive strength of composite columns provided by CECS 188:2005 is proved by the test results of this paper.

STUDY ON APPLICATION OF RECYCLED AGGREGATE CONCRETE TO THE COMPOSITE STRUCTURES

It is known that the axial strength of composite columns could be calculated by the strength superposing method due to the many experimental results of axial compression of composite columns. However, in case of the composite columns in which recycled concrete are used, the contribution of the confinement effect to the structural performance has not yet been clarified. Therefore, twenty-one composite columns were tested under axial compression loading to investigate the effects of concrete type, such as normal concrete, recycled aggregate concrete and fiber reinforced concrete. The application of recycled aggregate concrete to the composite structures are discussed in this paper based on test results.

Numerical simulation of concrete encased steel composite columns

This paper investigates the behaviour of pin-ended axially loaded concrete encased steel composite columns. A nonlinear 3-D finite element model was developed to analyse the inelastic behaviour of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement of the concrete encased steel composite columns. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered that allowed the bond behaviour to be modeled and the different components to retain their profile during the deformation of the column. Furthermore, the initial overall (out-of-straightness) geometric imperfection was carefully incorporated in the model. The finite element model has been validated against published experimental results. The main objective of the study was to understand the structural response and modes of failure of the columns and to assess the composite column strengths against current design codes. The study covered slender, non-slender, stub and long concrete encased steel composite columns. The concrete strengths varied from normal to high strength (20–110 MPa). The steel section yield stresses also varied from normal to high strength (275–690 MPa). Furthermore, the variables that influence the composite column behaviour and strength comprising different slenderness ratios, concrete strength and steel yield stress were investigated in a parametric study. It is shown that the increase in structural steel strength has a small effect on the composite column strength for the columns having higher relative slenderness ratios due to the flexural buckling failure mode. The composite column strengths obtained from the finite element analysis were compared with the design strengths calculated using the American Institute for Steel Construction AISC and Eurocode 4 for composite columns. Generally, it is shown that the EC 4 accurately predicted the design strength for the concrete encased steel composite columns having a concrete cylinder strength of 30 MPa and structural steel yield stresses of 275 and 460 MPa, which are in the limits of the code, which otherwise, was generally conservative. The AISC predictions were quite conservative for all the concrete encased steel composite columns.