Undergrad Thesis Presentation

AHSANULLAH UNIVERSITY OF SCIENCE

AND TECHNOLOGY (AUST)

Paper Title

“Investigation of axial capacity of RC columns made of steel fiber reinforced concrete (SFRC)”

1

Presented byRomana AkhterDepartment of Civil EngineeringAhsanullah University of Science and Technology (AUST), Dhaka 1208, Bangladesh

Co-Partners:Kazi Shahriar Islam

Rufaka Tabasum

Presentation Outline

I n t r o d u c t i o nO b j e c t i v eE x p e r i m e n t a l P r o g r a m

a n d S t r a t e g yE x p e r i m e n t a l D a t a

A n a l y s i sF i n i t e E l e m e n t M o d e l i n g

a n d A n a l y s i sV a l i d a t i o n o f F E r e s u l t sE v a l u a t i o n o f F a i l u r e

P a t t e r n sC o n c l u s i o n

2

SFRC

Steel

Fiber

Reinforced

Concrete

???? WHAT IS SFRC ????

3

Different shapes of steel fiber

Introduction

4

Types of steel fiber

Introduction

According to ASTM A 820/A 820M – 06, five general types of steel fibers are identified based upon the product or process used as a source of the steel fiber material, these are,

Type I: cold-drawn wire, Type II: cut sheet, Type III: melt-extracted, Type IV: mill cut, Type V: modified cold-drawn wire

5

6

SFRC ADVANTAGE

S

Enhancement of

ductility and energy

absorption capacity Improve

internal tensile

strength of the concrete

due to bonding force.

Increase the flexural

strength , direct tensile

strength and fatigue

strength.

Enhance shear and torsional strength

Shock resistance as well as toughness of concrete

Introduction

7

Fibers distribute

randomly and act as crack arrestors.

changing concrete from a brittle material to a

ductile one, in addition to improving

toughness and rigidity

Increases the ductility by

arresting crack and prevents

the propagation of cracks by

bridging fibers.

zone a: Free area of stresszone b: Fiber bridging area zone c: Micro-crack area zone d: Undamaged area

Introduction

Objective

8

To study the compressive behavior of SFRC RC columns due to different aspect ratios of steel fiber, i.e. 40, 60 and 80

To investigate the compressive and tensile behavior of SFRC RC columns of two different cross-sections

To examine failure patterns of RC columns made of SFRC.

To construct FE models for plain concrete and SFRC in the FE platform of ANSYS 11.0 and also to validate the models with the experimental results.

9

Important properties of steel fibers for fiber selection

Type of fiber Shape of fiber Aspect ratio (ratio of length to diameter, l/d) Quantity of steel fiber (volume ratio in %) Orientation of fiber

Experimental program and strategy

10

Selection of shape

Stress-strain curves for steel fiber reinforced mortars in tension (ACI 544.4R-88)


11

Materials

Sand Stone Cement Water Steel fiber


Cement type OPC (Ordinary Portland Cement)

Coarse Aggregate Size 1 in passing and 3/4 in retain (50%)3/4 in passing and 1/2 in retain (50%)

C:FA:CA 1:1.5:3

W/C 0.5

Slump 1in (25mm)

Fiber Volume 1.5%

Fiber Aspect ratio 40, 60 and 80

Fiber type End enlarged

Fiber Tensile strength 160000 psi (1100 MPa)

Fiber cross section Circular

Fiber diameter 1.18 mm

Concrete comp. strength 3700 psi (25.5 MPa)

Type of coarse aggregate Stone

12

Testing and Data Acquisition A digital universal testing machine (UTM) of capacity 1000

kN is used in this experiment. This is a displacement controlled machine. Load and displacement value can be measured from this UTM.

In this experiment displacement rate of 0.5mm per minute is applied.

Lateral displacements/strain are measured by analyzing the image histories obtained from high definition video camera and employing an image analysis technique which is called Digital Image Correlation Technique (DICT).


13


4-8mm

6in

6in 6in dia

4-8mm

15in 15in

Experimental strategy and reinforcement layout

14

Images of Experimental Testing and Data Acquisition


15

Effects on compressive strength

Experimental data analysis

Compressive strength test mechanism

16


Effects on compressive strength

0

1000

2000

3000

4000

5000

0 0.005 0.01 0.015

CSCCONCSC40

Co

mp

ress

ive

str

ess

(p

si)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

str

ess

(M

Pa)

0

1000

2000

3000

4000

5000

0 0.005 0.01 0.015

CSCCONCSC60

Co

mp

ress

ive

str

ess

(psi

)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

str

ess

(MP

a)

0

1000

2000

3000

4000

5000

0 0.005 0.01 0.015

CSCCON

CSC80

Co

mp

ress

ive

str

ess

(p

si)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

str

ess

(M

Pa)

17


Effects on tensile capacity Tensile strength test mechanism

18


Effects on tensile capacity

0

200

400

600

800

1000

1200

1400

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

CSTCONCST40

Ten

sile

str

ess

(ps

i)

Tensile strain

0

1.4

2.8

4.2

5.6

7.0

8.4

9.8

Ten

sile

str

ess

(M

Pa

)

0

200

400

600

800

1000

1200

1400

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

CSTCONCST60

Ten

sile

str

ess

(ps

i)

Tensile strain

0

1.4

2.8

4.2

5.6

7.0

8.4

9.8

Ten

sile

str

ess

(M

Pa

)

0

200

400

600

800

1000

1200

1400

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

CSTCONCST80

Ten

sile

str

ess

(ps

i)

Tensile strain

0

1.4

2.8

4.2

5.6

7.0

8.4

9.8

Ten

sile

str

ess

(M

Pa

)

19


0

1000

2000

3000

4000

5000

6000

0 0.005 0.01 0.015 0.02 0.025

CSSCCONCSSC40

Co

mp

ress

ive

str

ess

(psi

)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

str

ess

(MP

a)

42

48mm127X127X380mm

0

1000

2000

3000

4000

5000

6000

0 0.005 0.01 0.015 0.02 0.025

CSSCCONCSSC60

Co

mp

ress

ive

str

ess

(psi

)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

str

ess

(MP

a)

42

48mm127X127X380mm

0

1000

2000

3000

4000

5000

6000

0 0.005 0.01 0.015 0.02 0.025

CSSCCONCSSC80

Co

mp

ress

ive

str

ess

(psi

)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

str

ess

(MP

a)

42

48mm127X127X380mm

Effects on axial capacity

20


Effects on axial capacity

0

1000

2000

3000

4000

5000

6000

0 0.001 0.002 0.003 0.004 0.005 0.006

CSCCCONCSCC40

Co

mp

ress

ive

str

ess

(psi

)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

str

ess

(MP

a)

42

48mm

150X380mm

0

1000

2000

3000

4000

5000

6000

0 0.001 0.002 0.003 0.004 0.005 0.006

CSCCCONCSCC60

Co

mp

ress

ive

str

ess

(psi

)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

str

ess

(MP

a)

42

48mm

150X380mm

0

1000

2000

3000

4000

5000

6000

0 0.001 0.002 0.003 0.004 0.005 0.006

CSCCCONCSCC80

Co

mp

ress

ive

str

ess

(psi

)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

str

ess

(MP

a)

42

48mm

150X380mm

Finite Element modeling and analysis

21

FE elementSOLID65 is used to model the concrete and also SFRC. The solid is capable of cracking in tension and crushing in compression. The element is defined by eight nodes having three degrees of freedom at each node; translations in the nodal x, y, and z directions. The element is capable of plastic deformation, cracking in three orthogonal directions and crushing. In concrete applications, the element is also applicable for reinforced composites, such as, fiberglass and in this case fiber reinforced concrete (FRC). The geometry and node locations for this type of element are as follows:

FE element

LINK8 is a spar. The 3-D spar element is a uniaxial tension-compression

element with three degrees of freedom at each node: translations in the

nodal x, y, and z directions. As in a pin-jointed structure, no bending of the

element is considered. Plasticity, creep, swelling, stress stiffening, and large

deflection capabilities are included. The geometry and node locations for this

type of element has shown below:


22

Properties for FE model

SpecimenUnitCSSCCON CSSC40 CSSC60 CSSC80

Elastic Modulus 2200000 1936000 1936000 1936000 psi

Density 0.083 0.094 0.094 0.094 lb/in 3

Ultimate uniaxial tensile strength 558 884 1215 918 psi

Poisson’s Ratio 0.3 0.3 0.3 0.3 -

Displacement boundary condition (-y direction)

1.0 1.0 1.0 1.0 mm

Shear TransferCo-efficient for Closed crack

0.5 0.5 0.5 0.5 -

Shear TransferCo-efficient for Open crack

0.3 0.3 0.3 0.3 -

FE input data

Properties for FE model

SpecimenUnit

CSCCCON CSCC40 CSCC60 CSCC80

Elastic modulus 2200000 2200000 2200000 2200000 psi

Density 0.083 0.094 0.094 0.094 lb/in 3

Ultimate uniaxial tensile strength 558 884 1215 918 psi

Poisson’s ratio 0.3 0.3 0.3 0.3 -

Displacement boundary condition (-y direction)

1.0 1.0 1.0 1.0 mm

Shear TransferCo-efficient for Closed crack

0.5 0.5 0.5 0.5 -

Shear TransferCo-efficient for Open crack

0.3 0.3 0.3 0.3 -

Properties for FE model Reinforcement Unit

Density 0.283 lb/in 3

Yield stress 72,500 psi

Teng. Modulus 3,000 psi

Poisson’s ratio 0.3

Elastic modulus 30000000 psi


23

Finite Element modeling requires optimum mesh size for better analysis. A suitable mesh size helps to achieve sufficient accuracy and also saves time.

FE mesh analysis


24

Geometry of FE models

Volume With Reinforcement Boundary Condition

Evaluation of FE results

25

Stress-strain patterns

0

1000

2000

3000

4000

5000

6000

0 0.002 0.004 0.006 0.008 0.01

CSSCCONANSYS CSSCCON

Co

mp

ress

ive

stre

ss (

psi)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

stre

ss (

MP

a)

42

48mm127X127x380mm

0

1000

2000

3000

4000

5000

6000

0 0.005 0.01 0.015 0.02

CSSC40ANSYS CSSC40

Co

mp

ress

ive

stre

ss (

psi)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

stre

ss (

MP

a)

42

48mm127X127x380mm


26


0

1000

2000

3000

4000

5000

6000

0 0.005 0.01 0.015 0.02 0.025 0.03

CSSC60ANSYS CSSC60

Co

mp

ress

ive

stre

ss (

psi)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

stre

ss (

MP

a)

42

48mm127X127x380mm

0

1000

2000

3000

4000

5000

6000

0 0.005 0.01 0.015 0.02

CSSC80ANSYS CSSC80

Co

mp

ress

ive

stre

ss (

psi)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

stre

ss (

MP

a)

42

48mm127X127x380mm


27


0

1000

2000

3000

4000

5000

6000

0 0.0005 0.001 0.0015 0.002

CSCCCONANSYS CSCCCON

Co

mp

ress

ive

stre

ss (

psi)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

stre

ss (

MP

a)

42

48mm

150X380mm

0

1000

2000

3000

4000

5000

6000

0 0.001 0.002 0.003 0.004 0.005

CSCC40ANSYS CSCC40

Co

mp

ress

ive

stre

ss (

psi)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

stre

ss (

MP

a)

42

48mm

150X380mm


28


0

1000

2000

3000

4000

5000

6000

0 0.001 0.002 0.003 0.004 0.005 0.006

CSCC60ANSYS CSCC60

Co

mp

ress

ive

stre

ss (

psi)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

stre

ss (

MP

a)

42

48mm

150X380mm

0

1000

2000

3000

4000

5000

6000

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

CSCC80ANSYS CSCC80

Co

mp

ress

ive

stre

ss (

psi)

Compressive strain

0

7

14

21

28

35

Co

mp

ress

ive

stre

ss (

MP

a)

42

48mm

150X380mm

29

Evaluation of failure patterns& failure location

30



31

Conclusion

32

It was observed that steel fibers, up to approximately 1.5% by volume, can partially substitute for the transverse reinforcement in RC columns and hence could result in improved constructability.

It was also observed that fibers transform the cover spalling from a sudden mechanism to a gradual mechanism. The addition of fibers, however, did not prevent bar buckling from occurring.

The FE models showed similar analyses result compared to experimental outcomes which ensures good agreements

The failure patterns are also similar which validated the FE models.

The addition of steel fibers in reinforced concrete columns can lead to improvements, including an increase in peak load-carrying capacity of the column and a significant improvement in the post-peak response of the column. FE analyses have shown conservative results in most of the cases compared to experimental result which indicate sufficient factor of safety and also ensure a reliable FE model.

33

THANK YOU