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European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online: https://ejbss.org/ P a g e | 936

Experimental Study on Concrete Filled Steel Tube

Columns under Axial Compression

Senthilkumaran .C, PG Student

Dept. of Civil Engineering

PRIST University

Thanjavur-403, India

ersenthilkumaranbe@gmail.com

Abstract — Concrete filled steel tubes (CFST) have been more

and more applied in bridges, high-rise buildings, viaducts and

electricity transmission towers. In the past, a large number of

studies have been carried out on traditional straight CFST

columns, and some design codes have been developed worldwide.

During the whole life cycle, structures may inevitably suffer

from various impact loads. For example as the bridge pier, they

may be laterally crashed by vehicles or vessels. It is evident that

bridge piers always bear axial loads simultaneously when impact

accidents occur. Research has seldom been conducted on the

impact performance of CFST members, however. Axial impact

experiments on twenty-one circular are CFST columns were

studied. Bambach investigated the performance of square CFST

members subjected to lateral impacts at the beam mid-span, a

design procedure was also developed. The Impact resistances of

small-size micro-concrete-filled steel tubes under axial impact

loads at were experimentally studied.

The above mentioned research demonstrated that CFST

members have excellent impact resistance. However, there is a

lack of investigation on the performance of CFST members with

an axial load under lateral impact loads so it is necessary to

undertake further research on this issue. In this study is thus an

attempt to study the performance of CFST members with a

different axial load level subjected to lateral impact. The typical

failure modes and the time history of the impact forces for the

composite members were studied.

Index Terms— Concrete filled steel tubes (CFST),

Compression member

I. INTRODUCTION

Concrete is versatile, has desirable engineering properties,

can be molded into any shapes and more importantly is

produced with cost-effective materials. There is an old saying

that broken stone, sand, and cement make good concrete. But

the same proportion of broken stone, sand and cement also

make bad concrete. To make good concrete now variety of

innovative materials such as fibres, admixtures and

construction chemicals, pozzolanas and different concrete

making techniques are adopted in present day construction.

In recent years, intensive research has resulted in advances

and innovation in the technology of fibres such as glass,

polypropylene, carbon etc., and more basic knowledge has

been gained on the behaviour of cement concrete containing

these fibres

Large quantities of waste materials and by-products are

generated from manufacturing processes, service industries and

municipal solid wastes, etc. As a result, solid waste

management has become one of the major environmental

concerns in the world. With the increasing awareness about the

environment, scarcity of land-fill space and due to its ever

increasing cost, waste materials and by-products utilization has

become an attractive alternative to disposal. Bagasse is a

cellulose fiber remaining after the extraction of the sugar- bearing juice from sugarcane. Biomass is an important source

of energy in tropical countries like India.

High consumption of natural sources, high amount

production of industrial wastes and environmental pollution

require obtaining new solutions for a sustainable development.

Ordinary Portland cement is recognized as a major

construction material throughout the world. Significant

research has been going-on in various parts of the world on the

subject. Some waste materials and by-products have

established their credentials in their usage in cement-based

materials and for others research is in progress for exploring

the potential applications

II. CONCRETE FILLED STEEL TUBE

In the Concrete Filled Steel Tube (CFST) Structural System

high-strength concrete is used for filling steel tubes. These

members are ideally suited for all applications because of their

effective usage of construction material. CFST structure

is a type of the composite steel-concrete structures used

presently in civil engineering field.

In this type of composite members, the advantages of both

hollow structural steel (HSS) and concrete is utilized. Due to

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European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online: https://ejbss.org/ P a g e | 937

excellent static and earthquake resistant properties of CFST,

they are being used widely in real civil engineering projects.

They possess properties such as high strength, high ductility

and large energy absorption capacity. Concrete filled steel

tubes (CFST) are also used extensively in other modern civil

engineering applications. When these types of composite

members are used as structural columns, especially in high- rise buildings, they may be subjected to high shearing force as

well as moments due to wind or seismic actions.

Therefore it is very important to study the behaviour of

CFST Columns in axial compression. It may be noted here that

mechanical and economic benefits can be achieved by high

strength concrete infill, which contributes greater damping and

stiffness to CFST columns compare to normal strength

concrete. Moreover, high strength CFST columns require a

smaller cross section to withstand the load, which is

appreciated by architects and building engineers. Main

advantages of the interaction between the steel tube and

concrete are local buckling of steel tube is delayed due to

concrete infill and steel tubes provided sufficient confining

effect to concrete.

The enhancement of CFST column in structural system is

due to composite action between constituent elements. The

steel shell acts as longitudinal and transverse reinforcement.

The shell also provides confining pressure to the concrete,

which puts concrete under tri-axial state of stress. On the other

hand, the steel tube is stiffened by the concrete core. This can

prevent the inward buckling of steel tube, and increases the

stability and the strength of column system, resulting in higher

flexural strength.

Therefore tubes with thinner walls could reach the yielding

strength before local buckling. Under axial compression, the

steel tube confines the concrete, therefore improves both

axial load resistance and ductility of CFST members. Concrete

filled steel tubes are used in many structural applications

including columns supported offshore platforms, roofs of

storage tanks, bridge piers, piles and columns in seismic

zones.

Application of the CFST concept may lead to 60% total

saving of steel in comparison to conventional structural steel

system. Steel tubes were also used as permanent formwork and

the well distributed reinforcement located at most efficient

position.

III. TYPES OF CFST STRUCTURAL MEMBERS

Composite columns are structural members, which are

subjected mainly to axial compressive forces and end

moments. The general term ’composite column’ refers to any

compression member in which the steel element acts

compositely with the concrete as shown in fig 1. so that both

elements contribute to the strength. These columns have been

used widespread as they speed up construction by eliminating

formwork and the need for tying of longitudinal reinforcement.

Composite columns have recently undergone increased

usage throughout the world, which has been influenced by the

development of high strength concrete permitting these

columns to be considerably economized. Columns designed to

resist the majority of axial force by concrete alone can be

further economized by the use of thin-walled steel columns.

New developments, including the use of high strength concrete

and the credit of the enhanced local buckling capacity of the

steel has allowed much more economical designs to evolve.

The main economy achieved by using high strength

concrete in thin steel casings is that the structural steel cost is

minimized and the majority of the load in compression is

resisted by the high strength concrete.

The composite CFT column is well renowned for its

strength, good ductility and energy absorption capacity in

earthquake. This type of columns has also been proven to be

economical due to rapid construction, as the external steel

tubes may act as permanent and integral formworks which lead

to reduction in labour costs, materials and construction time.

The orientation of steel and concrete materials in a CFT

column is also beneficial in terms of enhancing the columns

stiffness and bending strength, as the steel tube has a greater

elastic modulus owing to the fact that the element is situated

furthest from the centroid of the cross section

Fig. 1. Various cross-sections of CFST composite column

A. Elliptical hollow section (EHS)

Elliptical hollow section (EHS) is a relatively new cross

section that has been introduced in the UK by CORUS. It

offers an additional choice to structural designers for its

structural efficiency and to the architects for its appearance.

This section may provide greater bending capacity compared to

the circular hollow section with identical area and weight, due

to its strong and weak axis directions. However, currently there

is limited understanding concerning the structural behaviour of

elliptical CFT columns. Presently, the design for the

compressive members with elliptical section shape has not

been covered by any Code of Practice, Specification or

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European Journal of Business &

Social Sciences

Available at https://ejbss.org/

ISSN: 2235-767X

Volume 07 Issue 05

May 2019

Available online: https://ejbss.org/ P a g e | 938

Standard. However due to the increases in the use of such

hollow section shape, broad study has been conducted to

provide an insight to the behaviour of this form of structures

Extensive researches have been carried out on short EHS

columns. These included experiments on typical steel hollow

sections with different wall thicknesses, normal to high

concrete infill strength, various loading cases including loading

compositely, loading on concrete core only and loading

through steel section only. From these studies, the effect of

the strength of concrete infill and wall thickness of steel

hollow sections on the structural behaviour has been

highlighted. Furthermore the comparison and analyses

showed that the effect of steel tube wall thickness was

especially sensitive in composite columns with normal strength

concrete as the capacity of the columns depends on the effect

of confinement that is provided by the steel tube. When the

concrete strength increases, the influence of wall thickness

becomes less significant.

B. Circular CFT columns

Researches on the ultimate strengths of elliptical carried

out by the authors with the square and circular CFT columns

carried out by Lam and Williams, and Giakoumelis and Lam

showed that the circular CFT columns were better than

elliptical CFT columns due to the circular hollow section

providing stronger confinement to the concrete core, higher

axial load may be achieved by elliptical CFT columns

compared to square and rectangular CFT columns. This

attributes to the curved section shape of the elliptical tube that

offers more circumferential tension which in turn provides a

higher confinement to the concrete core.

Further investigation on elliptical CFT columns carried out

by Yang et al. indicated that the wall thickness of the tube did

affect the axial compressive behaviour of this type of

composite columns. In- clined shear failure on the concrete

infill was observed in composite columns with smaller wall

thickness of the steel sections due to less confinement when

compared to composite columns with greater wall thickness of

the steel sections.

C. Concrete Contribution Ratio (CCR)

The relationship between cylinder strength and concrete

contribution ratio (CCR) demonstrated that the wall thickness

of the steel sections has direct contribution to the increase

capacity of the concrete infill. Experimental study on stub

elliptical CFT columns carried out by Zhao and Packer

considered both normal to high strength SCC concrete and

adopted different loading conditions. The simple superposition

approach in predicting the ultimate capacity of CFT stub

columns with elliptical hollow section (EHS) as an equivalent

of RHS was proposed to predict the capacity of elliptical CFT

columns.

Experimental study and numerical modelling on EHS

carried out by Gardner and Ministro included geometric

features, non-linear material properties and initial geometric

imperfections. Several amplitudes of initial geometric

imperfections were considered and it was found that the

structural behaviour of hollow sections was very sensi- tive to

the level of imperfection; however the ultimate load was

relatively less sensitive to the amplitude of the imperfection.

Paramet- ric studies with different section aspect ratios and

varying slenderness for elliptical hollow sections were also

carried out following the satis- factory validation of numerical

method against experimental results.

Preliminary effective area formulation for slender EHS was

also proposed in their study. An investigation on local buckling

behaviour of the EHS columns in compression was performed

by Zhu and Wilkinson. In their study the term “equivalent

CHS” was used to model the local buckling of EHS. The

diameter term, D in theoretical elastic buckling load of a

circular hollow was replaced by D2/D which represents the

major and minor diameters of the ellipse. It was confirmed that

the use of an equivalent CHS was a reasonably good predictor

for the capacity of slender sections and the deformation

capacity of compact sections.

Numerical studies on elliptical CFT columns have been

carried out by the authors, a new confined concrete model

were developed for the elliptical CFT columns. However, as

for columns with high strength concrete (HSC), the confined

concrete properties has little effect to the behaviour. This is

due to the increment of the compres- sive strength and

stiffness of high concrete has little confinement ef- fect at the

failure stage as the steel hollow section has already yielded.

Further numerical simulation on elliptical CFT columns was

carried out by Dai and Lam Based on the comparison and

analysis against experimental results available, a modified

stress–strain model was proposed. In this model, a ‘quick

softening’ section was introduced to consider the effect of

elliptical geometric feature. This modified model has been

used successfully in prediction of axial compressive load and

failure modes of stub elliptical CFT columns.

IV. LITERATURE REVIEW

All codes assume full interaction, but some impose

restrictions on the shear stress at the steel-concrete interface. It

is customary to use direct bearing or provide shear connectors,

if used where the specified limiting shear stress is exceeded.

• Dennis Lam, EhabEllobod and Ben Young had

concluded that, the results of the parametric study showed that

the column design rules specified in the American

Specifications and Australian Standards are conservative.

However, the design strengths predicted by the Eurocode 4 are

generally unconservative. The column design rules in the