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METNET Seminar, March 13, 2013, VGTU, Vilnius, Lithuania

RESEARCH IN THE FIELD OF

CONCRETE-FILLED STEEL TUBULAR

STRUCTURAL MEMBERS IN VGTU

Audronis Kazimieras Kvedaras, Antanas Šapalas

Vilnius Gediminas Technical University, Dept. of Steel and Timber

Structures, Lithuania

INTRODUCTION

The concrete-filled steel tubes now obtain wider application in construction practice.

a) b) c) d)

Fig. 1: Composite sections with annular (a, c) and solid (b, d) concrete cores

METNET Seminar, March 13, 2013, VGTU, Vilnius, Lithuania // A.K.Kvedaras & A.Šapalas


The composite steel and concrete members of annular cross-section are quite efficient tubular structures. Structurally and economically rational for columns, beams and beam-columns are especially such members with hollow concrete cores.

However, the structural performance and reliability of this new type of tubular members are investigated not well enough in spite of some recommendations existing in approved EN 1994-1-1 (Euro code 4).

The main task of this report is presenting the methodical formats for behaviour verifications of tubular composite steel and concrete members of buildings assisted by

testing and based on semi-probabilistic approaches.


1. Performance of composite cross-section

It is necessary simply to pay your attention that on the

behaviour of stubby compressed members the resistance

checking of columns, beams and beam-columns is based

by simplified methods.

The interaction between the concrete filled tubes of

circular cross-section components’ interfaces occurring

under compression is calling an increase in strength of

both components and the robustness of the whole

composite member against the member resistance

defined by superposition criterion. That is proved by

numerous test data and results of plastic analysis.

But according to EN1994-1-1 account may be taken of

increase in strength of concrete caused by confinement

provided that the relative slenderness λ does not exceed

0.5 and e/d < 0,1. By the General method of design even

so full composite action up to failure may be assumed

between the steel and concrete components of a member.

For definition the resistance of members in combined

compression and uniaxial bending the value of plastic

bending resistance Mpl,Rd it is necessary to know. There

are no recommendations in EN1994-1-1 how to define

the value of this moment in spite of some peculiarity of

such procedure because of circular shape of cross-section.



Therefore, appealing to the above description of the General

method of design about possibility to assume full

composite action up to failure between the steel and

concrete components of the concrete filled tubular

member we carried out the experimental and theoretical

investigation of behaviour of concrete filled tubular

columns, beams and beam-columns.

An approach of above mentioned interaction description

should be based on the postulates the theory of plasticity

of the small elasto-plastic strains and shall to take into

account different values of Poisson’s ratio of components

and an appropriate definition of the strain criteria.


x x

y

y

zz

x

x xx

N N N

N N N

d

d d

tt

= +

( )a ( )c ( )d( )b

a c

e

ci ce

ca c

z

z

z

z

Fig.2: Diagrammatic sketch of concentric actions on the

hollow composite member (a), steel tube (b) and hollow

concrete core (c); shape and dimensions of hollow cross-

section (d)


zyxim

Ex

εεσ v,

34

From the generalized Hooke’s law, the normal ultimate

stresses of both media have to be expressed so:

where: is the secant modulus of elasticity;

and

are the values of longitudinal and tangential strains,

respectively. Because of the assumed biaxial stress

state for both components the ultimate normal

stresses from Eq. represent the modified values of

components’ strengths.

imE

22, 35.0 ziyzyx axzz E 5.0

and,

where and (1.640 – for solid core) are the

mean value of constraining factors which characterize the

interaction effect of components;

, values of steel yield and concrete specified

compressive strength (Figs 3 and 4)

The rationality of tubular composite members under

compression demonstrates the efficiency factor

the mean value of which in our

tests was equal to 1.17.


yf

aaxaf ησ

cf

ccxcf ησ

0741= .a 320.1cη

'

cfyf

ccaytref AfAfRK

Fig. 3. Stress-strain relationship of steel under the unblocked (1) and the blocked (2) strains (in scale of generalized stresses and strains)


1f

f2

ai

y

a y

ai

0

Fig. 4. Stress-strain relationship of concrete under unblocked (1) and

blocked by typical (2) and bi-linear (3) strain laws (in scale of

generalized stresses and strains)


1

f

f

0 0.5

c c

c

ciciuciu

2

3

ci


Because of the assumed equality of biaxial stress state in

steel shell and in concrete core, the ultimate value of the

generalized strain will be the same for both

materials. This generalized strain for concrete-filled steel

tube expresses the deformation criterion corresponding

to the yield strength of shell steel. When the thickness

of a steel tube is less than its ultimate minimum critical

steel strength has to be used instead of .

The second deformation criterion may correspond to the

shear yield strength of shell steel (that might agree with

the ultimate tensile strength ) but at initial design stages

this criterion is unusfull because of not standardised

value of limit of proportionality of steel.

ayiy Ef5.1

crf yf

yf

uf


COMPARISON OFCALCULATIONS AND EXPERIMENTAL DATA


2. RESISTANCE OF COLUMNS

It was taken recommendation of euro code EC4 that for

simplification for members in axial compression, the

design value of the normal force should satisfy:

Where

is the reduction factor for the relevant buckling mode

in terms of the relevant relative slenderness .

EdN

0,1Rdpl,

Ed N

N

sdscdccydaaRdpl, fAfAfAN

3. RESISTANCE OF BEAM-COLUMNS

If to take recommendation of euro code EC4 the following

expression based on the interaction curve should be

satisfied:

That means necessity to find the value of bending moment

for quite specific circular cross-section. Earlier in BS

5400 and in drafts of EC4 the expressions were

recommended, but in approved version of EC4 no more

similar expressions exist.


M

Rdpl,d

Ed

RdN,pl,

Ed

M

M

M

M

Therefore, we investigated this problem and discovered that

bending moment of circular concrete-filled steel tube may

be expressed so:

Mpl,Rd=Npl,a,Rd eu , where Npl,a,Rd=ηa Aafyd

The corresponding relationship is used to find a magnitude

of this design eccentricity eu:



Fig. 5. Dimensions of cross-section of hollow concrete filled circular

steel tubular beam and position of plastic neutral axis


Polythene concrete-filled tubes after test (l = 600 mm) and before test (l=1200 mm)

Polythene concrete-filled tubular beam-columns (l =1800 mm and l = 2400 mm)


Polythene concrete-filled tubes after a simple bending test (l = 1800 mm)


FULL SCALE TESTING OF LATICE COLUMNS


APPLICATION (1)

• 1250

D=340

CROSS SECTION OF COLUMN


APPLICATION (2)


APPLICATION (3)


1

2

3

APPLICATION (4)


THANK YOU FOR YOUR

KIND ATTENTION!


research in the field of concrete-filled steel tubular ... 2013/presentations/metnet workshop... ·...

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