Metallurgical and Mining Industry6 No.12 — 2015

Application of metalproducts

Analysis on the Impact Behavior of Super High Strength Concrete Filled Steel Tube Columns

Zhishuo Yang1, 2

1 College of Civil Engineering, Putian University, Putian 351100, Fujian, China

2 College of Civil Engineering and Architecture, Central South University, Changsha 410081, Hunan, China

Mingxia Chen

College of Civil Engineering, Putian University, Putian 351100, Fujian, China

AbstractThis paper investigates the strength and behavior of super high strength Concrete-filled steel tube (SHSCFST) column under axial compression. The elastic-plastic damage theory is developed. Correspondingly, the user subroutines UMAT have been programmed for definition of their mechanical constitutive relations. The preprocessing and the finite element analysis of (SHSCFST) column are done using the commercial software system Abaqus. Specimens, with concrete strengths ranging 100MPa and with 219mm circular hollow stub columns with wall thicknesses 4 mm, were manufactured. A comparative study between simulation and experimental results shows that the simulation model is reliable and efficient.Key words: DAMAge THeory, UMAT, PyTHon, ABAQUS, ConCreTe-FilleD STeel TUBe.

1. introductionConcrete filled steel tubes (CFST’s) are used in-

creasingly as structural columns due to their excel-lent structural and constructional advantages. These members are often used at the frontage of buildings, in car parks and airports, or as bridge piers. There-fore, considerable research efforts were devoted to investigate the concrete-filled steel tubular (CFST) columns.By using different rigorous analysis meth-ods (see for example refs. [1,2]), simplified design approaches have been developed for them. These de-sign approaches were included in modern codes such

as eC4 [3] and AiSC [4]. To reduce the weight of the CFST columns without affecting the capacity against different loading cases, SHSCFST columns were pro-posed. in recent times, SHSCFST columns have been studied in literature [5–16] focusing mainly on short columns with common concrete.

With the development of economy and the de-pletion of resources, the concrete-filled steel column should get higher performance. [17–21] So being higher with the specific strength, and lower with the consumption of natural resource and the cost in their life cycle, reactive powder concrete as the rep-

7Metallurgical and Mining IndustryNo.12 — 2015

Application of metalproductsresentative of green super high strength concrete is of a promising application and has become the focus of research and application on the modern concrete. However, the structural behavior of concrete-filled tube columns is affected by many factors, such as member material properties, column slenderness and the geometry of steel section. Simultaneously domes-tic and foreign researches on super high-strength con-crete composite members are rare. This necessitates search for the compressive behavior of the super high strength concrete used stone-chip steel tube columns.

Hence, to enable better understanding of the compressive behavior of the ultra-high strength con-crete-filled steel tubular columns, the constitutive relation of the super high strength and high perfor-mance concrete was studied. Therefore, first, the con-stitutive relation is derived by plastic damage model. Second, this paper is providing new results dealing with the nonlinear analysis, behavior and design of circular SHSCFST columns. This is made by using the general purpose finite element (Fe) package AB-AQUS [22]. in this paper, with ForTrAn language, the UMAT was developed on the basis of ABAQUS plat form. Finally, validation of this numerical meth-od is carried out by comparing the simulation results with the experimental observation

2. Theoretical of constitutive relationThe theory is based on the elastic energy equiva-

lence principle. The basic mathematical relations of plastic damage model are as follows :

( )

( )( )

( ) ( )

~ ~

0~

2

0

20

, 1 ,1

1

1

1

σσ ε ε

ε ε

σ ε ε

= = − −

=

− = − = − −

eij e

ij ij ij

ijklijkl

e eijkl ij kl

pij ijkl kl kl

DDE

ED

Y D E

E D

(1)

ε ij = the strain tensor components;σ ij =the stress tensor components; p and e=Plasticity and elasticity;

~=Virtual static material parameter; D=Damage Variable ;y=Damage of Conjugate Stress0

ijklE = The elastic tensor of a non damaged materialDefined stress three axis ratio :

~

~

2~

2

3 02

，γ = ≠I

JJ

(2)

~

1I = sum of the effective stress value;~

2J = effec-tive stress deviation of second invariants ~

~ ~ ~ ~ ~ ~ ~ 11

1, ,2 3

σ σ= = = −ij ij ij ij ijJI J s s s

(3)~

ijs = Virtual stress tensor.Then γ introduces to damage plastic loading con-

dition and non elastic potential function, the function expression is as follow

( )1 2~ ~ ~

1 2 1 0λα −∞

= + − + − ≤ b

Ff I J k k e (4)

( )

1~1-

1

+ = + +

sS YF Q Ds S (5)

αF = Material constant, k= initial shear strength constant;

∞k = Strain hardening limit of virtual static mate-rials;

B= Model constant;~Q is the plastic part of the non elastic potential

defined in the effective stress space:

( )[ ]λα bq ekkJIQ −

∞ −+−+= 121

2

~

1

~~

(6)φ is the plastic strain increment

( )

+

−=

∂∂

=∂∂

=2

.~...

21 Js

DQF ij

ijQijij

p

ij δαλσ

λσ

λε (7)

Here, .λ = damage plastic multiplier and D= the

rate of damage evolving

( )

. . .1 ϕλ λ

γ

− = − =

sYD D YS (8)

S andφ= Material parameters, the eq.(8) is to be linear processing:

—

λ∆ = ∆D Y (9)λ∆ = initial value of Damage plastic multiplier

.~ ~

0= =f f (10)

λ ε∆ = ∆kl

klAB (11)

( )

~

20 1σ∂

= −∂kl ijkl

ij

fA E D (12)

( ) ( )~ ~ ~ ~

_20 01 2 1 εσ σ σ λ∂ ∂ ∂ ∂ ∂

= − + − − −∂ ∂ ∂ ∂ ∂

eijkl ijkl kl

ij ij ij

f Q f f fB E D E D YD

(13)

Metallurgical and Mining Industry8 No.12 — 2015

Application of metalproducts

1~~

0 0λ λλ

− ∂ ∆ = ∆ − ∂∆

ff

(14)At last ijklE (= stiffness tensor of elastic plastic tan-

gent) is obtained by (15) and update the new stress and other data

0 2(1 )= −ijkl ijklE E D (15)3. Processes and interface

This paper studies SHSCFST column using Abaqus secondary development. By using secondary development, SHSCFST column are modified individually. SHSCFST column can be obtained at different concrete, plate and steel pipe. Some operations, such as modifying geometry models, submitting tasks, and restarting analysis, are realized using python in the analysis procedure. With ForTrAn language, the UMAT was developed

Figure 1. The part and mesh of SHSCFST columnon the basis of ABAQUS plat form. Therefore, the computation efficiency of numerical simulation is improved. For study of SHSCFST column, some representative components are created, as shown in

Figure 1. 4. Verification4.1. MaterialThe measured unconfined compressive cube

strengths for concrete grades see table 1, respectively.

Mix

Cement Silica fume

Flyash sand Crushed stone Superpla-

sticizer Water-binder ratio basalt fiber cuf

% % % % % % % % aMP

10.95 1.73 0.012 0.21 0.012 100

1 0.171 0.526

Table 1. Mix of extra-high strength concrete mixed with stone-chip

Where, = compressive strength (Standard test block: 150*150*150)

Specimen number

×D t Dt

L LD yf

mm mm aMPB 219×4.0 54.7 740 3.4 235

Table 2. Parameters of specimens

Where , D= outer diameter of steel tube, t= thickness of the steel pipe, l= length of steel tube, yf =yield strength of steel tube.

9Metallurgical and Mining IndustryNo.12 — 2015

Application of metalproductsTable 2 shows the measured dimensions and material properties of the circular hollow sections.

4.2. Testing To understand the basis of the numerical model-

ing method and assess the accuracy of the numerical simulations, it is necessary to provide a description of the physical tests and the main experimental obser-vations. All tests were performed in a yAW-800 col-umn testing machine at College of Civil engineering of Putian University. For each test specimens, axial load, axial displacement from the test machine comes with software to automatically capture. Axial lateral

strain through DH3818 static strain gauge automates data acquisition and storage by a computer and the data acquisition frequency is 2 times per second. The test set-up is shown in Figure 2. While minute eccen-tricities might occur, every effort has been made to reduce the effect of the eccentric loading to ensure that the columns were concentrically and uniformly loaded. The tests were conducted using a universal testing machine with a capacity of 8000 kn. The load was applied in an increment of 50 kn before peak load. each load interval was maintained for 2–3 min. The load was slowly applied near and after the peak

Figure 2. . Test set up and result.

Figure 3. Axial load (n) versus end shortening (∆). Figure 4.Failure modes of specimens

load to investigate the post-peak behavior of the spec-imens. The results like Figure 3 and Figure 4 .

4. 3. Comparison between the numerical and experimental results

With ForTrAn language, the UMAT was devel-oped on the basis of ABAQUS plat form. With this UMAT, which was based on the constitutive equation

of this paper, ABAQUS can calculate Cauchy stress, plastic strain and damage. numerical results of field variations obtained with the new implemented model have been exported to the oDB file which is the stor-age file of numerical results prepared for pastprocess via UVArM subroutine as show Figure 1. Figure 5 is results of typical Fe model

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Application of metalproducts

Figure 5. results of typical Fe model

Figure 6. Comparison of maximum loads from experiments and numerical prediction

The accuracy of the finite element model devel-oped through the ABAQUS/Standard solver com-bined with the proposed stress–strain model for the confined concrete was verified by comparing the numerical results with the experimental results. The maximum compressive load, load versus column end-shortening and the column deformed shape were investigated. Figure 6 shows a comparison between the maximum axial compressive loads obtained from the experiments and the maximum axial compressive loads predicted by the finite element models: very good agreements have been obtained. The maximum difference observed between the experimental and numerical results is not more than 5%.

5. Conclusionsin the present research, a SHSCFST column for

engineering applications is developed. The conclu-sions as follows could be drawn as follows.

By coupling Abaqus and Python script, a para-

metric model for SHSCFST column is established. Though customized parametric simulation modeling, the SHSCFST column parameters could be modified by using the second exploitation interface. By analyz-ing and experimental results, it could be found that obtained results are in good agreement with experi-ment, whose prediction precision is in the acceptable range.

AcknowledgementsThis work was financially supported by the nat-

ural Science Foundation of Fujian Province, China (grant no. 2011J01327). This project is supported with the fund from the education fund item of Fu-jian province(grant no.JA12292).The fund projects are advanced civil engineering application technol-ogy and management research innovation team of Putian University , Civil engineering (Key discipline of Putian University) and advanced steel structure technology and application of Putian University . The authors gratefully acknowledge this support..

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