finite element modeling, analysis and validation of the shear capacity of rc beams made of steel...

AHSANULLAH UNIVERSITY OF

SCIENCE AND TECHNOLOGY (AUST)

FINITE ELEMENT MODELING, ANALYSIS AND VALIDATION OF THE

SHEAR CAPACITY OF RC BEAMS MADE OF STEEL FIBER

REINFORCED CONCRETE (SFRC)

1

Presented by:

Md. Shahadat HossainDepartment of Civil Engineering

Ahsanullah University of Science

and Technology (AUST),

Dhaka-1208, Bangladesh

Co-Authors:

Md. Mashfiqul Islam

Saiful Amin

Zahidul Islam

Mana Bala

Md. Arman Chowdhury

Ashfia Siddique

Paper ID: SEE 075

2

SFRC

STEEL FIBER REINFORCED CONCRETE

3

OPC(Hydraulic cement &

Admixtures)

Fine & Coarse aggregates

Dispersion of Short Discrete

Steel Fiber

SFRC

components

4

SFRC ADVANTAGES

Enhancement of ductility and energy absorption

capacity transforms failure modes from brittle

and dangerous shear failures into

more ductile flexural failures

Increase the flexural strength

, direct tensile strength and

fatigue strength.

Enhance shear and torsional strength

Shock resistance as

well as toughness of

concrete

Increasesstiffness , reduces

deflections

5

Applications of SFRC

• industrial or factory pavements, highways, roads, parking areas , airport runways

• tunnel linings,

• pre-cast structures, structures in high seismic risk areas, bridge decks

• off-shore platforms, water-retaining structures etc.

6

PC

(reinforced) SFRC

Mechanism of SFRC

Fibers distribute randomly and act as crack arrestors.

Resistance to crack extension provided near a crack tip(zone a) by the bond stress between fibers and concrete

Increases the ductility by arresting crack and preventsthe propagation of cracks by bridging fibers.

7

zone a: Free area of stress

zone b: Fiber bridging area

zone c: Micro-crack area

zone d: Undamaged area

When steel fibers are added to a

concrete mix :

8

To investigate the performance of steel

fiber with three different aspect ratio,

i.e. 40, 60 and 80

To evaluate the shear capacities of SFRC RC beams due to aspect ratio of steel fibers.

To examine failure patterns of RC beams

made of SFRC.

To construct FE models for plain

reinforced concrete and SFRC in the FE platform of ANSYS

11.0 and also validate the models with the

experimental results.

Above all to

provide the

construction

industry of

Bangladesh

with reliable

experimental

data and

validated FE

modeling

about this

engineering

material.

9

Experimental program and strategy

Experimental strategy

Experimental program

Specimen preparation

Testing and Data Acquisition

Investigation of failure

pattern

FE modeling through

optimizing the basic

engineering properties

FE analysis applying

experimental loading

environment and

displacement boundary

conditions

Validation of FE models and

analyses with experimental

results and failure modes

Strategy:Three different aspect ratio of steel fibers are selected

i.e. 40, 60 and 80 and prepared manually in thelaboratory. The beams are designed with 2-12mmφ

rebars(Figure-1) at bottom and without any web

reinforcement(Figure-2). The Rebars are connected to

provide anchorage at the end instead of making hook.The strategy is to estimate the shear capacity

increament due to steel fiber in the concrete mix and

also to evaluate the performance of fibers with respectto aspect ratio.

10

Figure1: Longitudinal

reinforcement

Figure 2: Experimental strategy

on shear beams.

11

Materials

Steel Fibers: Source types and shapes

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, they are,

Type I: cold-drawn wire,

Type II: cut sheet,

Type III: melt-extracted,

Type IV: mill cut,

Type V: modified

cold-drawn wire and

the fibers shall be

straight or deformed.

12

Typical Steel Fibers

13

Selection of shape

Stress-strain curves for steel fiber reinforced mortars in

tension

(ACI 544.4R-88)

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Fiber preparation

The fibers are prepared manually in the laboratory.

The cold drawn wires are cut from the coil as desired

length to make the required aspect ratio. In this

research the ends of the fibers are bended 120˚ to

make enlarged ends which provide anchorage in the

concrete matrix. Figure 3 shows the fiber preparation

and images of the prepared fibers.

15

16

Figure 3 : (a) Preparation of steel fibers (b) steel fibers of different

aspect ratio.

(a) (b)

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Three different types of steel fiber aspect ratio (l/d) i.e.

40, 60 and 80 are selected to be made. Their

corresponding measurements are given in the table-1

and shown in figure 4.

Aspect ratio

of steel fiber

Diameter

(mm)

Effective

length

(mm)

Original

length

(mm)

Angle

(Degree)

40 1.18 47.2 67.2 120

60 1.18 70.8 90.8 120

80 1.18 94.4 114.4 120

Aspect ratio:

Table1: Steel fiber size and geometry

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(a) (b)

Figure 4: (a) Size and geometry of steel fibers (b) image of fibers

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Aggregates

Crushed stone are used as coarse aggregate in this

research. Different types of aggregate are shown in

Figure 5.

Figure 5: (a) Stone aggregate (CA) and (b) Sand (FA)

(a) (b)

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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 dia 1.18 mm

Concrete comp. strength 3700 psi (25.5 MPa)

Type of coarse aggregate Stone

Table 2: Mix design of plain reinforced concrete and SFRC

Mix design

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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(Figure 6&7) and employing an image analysis

technique which is called Digital Image Correlation

Technique (DICT).

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Figure 7: Horizontal data acquisition

system via DICT.

Figure 6: Experimental setup for shear

critical beam in the UTM.

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Images of Experimental Testing of Simply Supported Beam

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0

1000

2000

3000

4000

5000

0 0.005 0.01 0.015

CSCCONCSC40CSC60CSC80

Co

mp

ressiv

e s

tress (

psi)

Compressive strain

0

7

14

21

28

35

Co

mp

ressiv

e s

tress (

MP

a)

2691 psi (19 MPa)

3741 psi (26 MPa)

4400 psi (30 MPa)

3733 psi (25.7 MPa)

Fig. 8: Experimental results of plain concrete and SFRC cylinder (a) compression

(b) splitting tension

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

CSTCONCST40CST60CST80

Tensile

str

ess (

psi)

Tensile strain

0

1.4

2.8

4.2

5.6

7.0

8.4

9.8

Tensile

str

ess (

MP

a)

(a) (b)

25

(a)

Fig. 9: Experimental results of plain reinforced concrete and SFRC beam (a) load

deflection behaviour of beams.

0

5

10

15

20

25

30

35

0 0.5 1 1.5 2

CSBSCCONCSBSC40CSBSC60CSBSC80

Lo

ad

(kip

)

Mid point deflection (in)

0 12.7 25.4 38.1 50.8

Mid point deflection (mm)

0

22

44

66

88

110

Lo

ad

(kN

)

132

154

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FE modeling

* Suitable element type

* Adequate mesh size

* Optimized material properties

* Appropriate boundary conditions

* Realistic loading environment

* Proper time stepping

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SOLID65 is used in ANSYS 11.0 to model the concrete and also SFRC, which is a three

dimensional (3D) solid element having eight nodes with three degrees of freedom at each

node, i.e., translational in the nodal x, y, and z directions. The element is capable of plastic

deformation, cracking in tension, crushing in compression and is also applicable for

reinforced composites (ANSYS 2005), such as, fibreglass, SFRC etc.

The flexural reinforcement is modelled using LINK8 element, which is a 3D spar element

as well as a uniaxial tension-compression element with three degrees of freedom at each

node same as SOLID65. The geometry and node locations for SOLID65 and LINK8

elements are shown in Fig.

FE element:

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FE models

(a)

(b)

Figure 9: Typical diagram of FE model of Shear-critical RC beam in ANSYS 11.0

(a) volume and (b) after meshing.

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FE governing parameters

Modulus of elasticity

Stress-strain behaviour

Poisson’s ratio

Density

Willum and Warke (1975) criterion

Shear transfer coefficient for open crack

Shear transfer coefficient for close crack

Tensile strength

Compressive strength

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Properties for FE

model

Beam specimen (SOLID65)

Rebar

(LINK8)CSBSCCON CSBSC40 CSBSC60 CSBSC80

Modulus of

elasticity3000000 psi 1870000psi 1400000psi 1400000psi

Density 2.69g/cm3 2.77g/cm3 2.72g/cm3 2.74g/cm3 7.8g/cm3

Tensile strength 4 Mpa 6 MPa 8 MPa 6.3 MPa -

Poisson’s ratio 0.325 0.325 0.325 0.325 0.3

Displacement

boundary

condition (-y

direction)

0.5mm 0.5mm 0.5mm 0.5mm

Shear transfer co-

efficient: closed

crack

0.25 0.5 0.5 0.5 -

Open crack 0.3 0.3 0.3 0.3 -

Yield stress- - - - 420 MPa

Table 3: FE input data for SOLID65 and LINK8 element

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0

5

10

15

20

25

30

35

0 0.5 1 1.5 2

ANSYS CSBSCCONCSBSCCON

Load

(kip

)

Mid point deflection (in)

0 12.7 25.4 38.1 50.8

Mid point deflection (mm)

0

22

44

66

88

110

Load

(kN

)

132

154

Fig. 4: Evaluation of load deflection behaviour FE and experimental

SC beams a) CSBSCCON i.e. control beam b) CSBSC40

0

5

10

15

20

25

30

35

0 0.5 1 1.5 2

ANSYS CSBSC40�CSBSC40

Load

(kip

)

Mid point deflection (in)

0 12.7 25.4 38.1 50.8

Mid point deflection (mm)

0

22

44

66

88

110

Load

(kN

)

132

154

(a) (b)

32

Fig. 4: Evaluation of load deflection behaviour FE and

experimental SC beams a) CSBSC60 b) CSBSC80.

0

5

10

15

20

25

30

35

0 0.5 1 1.5 2

ANSYS CSBSC80CSBSC80

Load

(kip

)

Mid point deflection (in)

0 12.7 25.4 38.1 50.8

Mid point deflection (mm)

0

22

44

66

88

110

Load

(kN

)

132

154

0

5

10

15

20

25

30

35

0 0.5 1 1.5 2

ANSYS CSBSC60CSBSC60

Load

(kip

)

Mid point deflection (in)

0 12.7 25.4 38.1 50.8

Mid point deflection (mm)

0

22

44

66

88

110

Load

(kN

)

132

154

(a) (b)

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Fig. 6: Experimental and FE failure pattern (a) CSBFCCON

(b)CSBFC40

(a) (b)

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Fig. 6: Experimental and FE failure pattern (a) CSBFC60

(b) CSBFC80.

(b)(a)

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Shear strength of SC beams increased about 25%, 29%and 18% for the SFAR 40, 60 and 80 respectivelycompared to control specimen.The ductility isenhanced 1.33, 1.58 and 1.17 times respectively.

The FE models showed similar analyses resultcompared to experimental outcomes which ensuresgood agreements

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

FE models showed conservative results which ensureadequate factor of safety as well as reliability of FEmodeling and analyses.

Further investigation shows the capability of themodels to predict capacity enhancements due to SFRCwhich ensures reliability of FE models.