Strength Enhancement in Concrete Confined by Spirals

8/3/2019 Strength Enhancement in Concrete Confined by Spirals

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Strength Enhancement inConcrete Confined bySpirals

Supervised by:

Dr. K. Baskaran

Group Members:U. Kaneswaran

J. Reginthan

H.M.P. Perera


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Introduction & Experiment

1H.M.P. Perera


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Introduction

This is not a widely used technology inconstruction industry

Strength of the concrete can be

enhanced by the confinement effectusing spirals

Confinement increases the ductility of

concrete The spiral reinforcement can be used

to prevent the punching shear failure

of flat slabs


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Introduction cont..

The shear carrying capacity of spiral is

due to,

Direct tension induced in spirals

Enhanced strength of concrete due to

confinement


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Failures Due to Lack ofConfinement


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Advantages of Using Spiral toIncrease the Confinement

Increase the ductility and strength ofthe concrete

Prevent spalling of concrete Prevent buckling of longitudinal

reinforcement

Give good response to seismic effect Give warning before failure

Easy to install


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Objectives

Determine the anchorage depth of thespiral

Identify the shear strength

enhancement in beams due to spiralreinforcement

Identify the shear strength

enhancement in flat slab due to spiralreinforcement

Find the equation to calculate shear

enhancement in beams


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Experiment 1

Diameter of the spiral = 118mm

Diameter of steel = 5.8mm

D = Embedded depth inside the concrete


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Testing arrangement


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Experiment Results

Depth of spiral (mm) Failure load (kN) Mode of failure26 7.32 Pullout33 11.12 Shear43 13.35 Shear48 16.46 Block shear53 18.91 Fracture of steel58 17.8 Fracture of steel60 17.8 Fracture of steel61 15.57 Fracture of steel63 15.57 Fracture of steel66 13.35 Fracture of steel68 13.35 Fracture of steel


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Mode of Failures

Pullout Failure Shear Failure


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Mode of Failures cont.

Block Shear Failure Fracture of Steel


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Conclusion RegardingExperiment 1 The anchorage depth of the spiral is

26mm

The anchorage depth depends on the

strength of concrete and diameter ofspiral


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Experiment 2 & 3

J. Reginthan


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Experiment 2

Beam Identification Description

Beam A Without any reinforcement

Beam B Reinforced with 2 Nos. of T16 bars at the bottom

Beam C

Reinforced with 2 Nos. of T16 bars at the bottom

and the spiral having the pitch of 30 mm and

108 mm centre to centre diameter


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Testing Arrangement


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Experimental Results

Failure loadsBeam Identification Failure Load (kN)

Beam A 17.66

Beam B 109.87

Beam C 155.00

0

50

100150

200

A B C

Load

(kN

)

Beam


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Experimental Results cont..

Failure modesBeam Identification Failure Mode

Beam A Flexural

Beam B Shear

Beam C Shear

Flexural Failure Shear Failure


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0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Load

(kN)

Deflection (mm)

Load VS Deflection

Beam A

Beam B

Beam C


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-6.00

-4.00

-2.00

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00

Strain

(10-6)

Load (kN)

Strain VS Load

CH 1

CH 2

Beam C


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Experiment 3

Beam Identification Description

Beam D Reinforced with 2 Nos. of T16 bars at the bottom

Beam E Reinforced with 2 Nos. of T16 bars at the bottom

and the spiral having the pitch of 30 mm and 108mm centre to centre diameter

Beam F Reinforced with 2 Nos. of T16 bars at the bottom

and the spiral having the pitch of 45 mm and 108

mm centre to centre diameter

Beam G Reinforced with 2 Nos. of T16 bars at the bottomand the spiral having the pitch of 60 mm and 108

mm centre to centre diameter


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Failure loadsBeam Identification Failure Load (kN)

D 109.87

E 149.11

F 139.30

G 127.53

0

50

100

150

D E F GBeam

Load

(kN

)


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0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

Load

(kN)

Deflection (mm)

Load Vs Deflection

Beam D

Beam E

Beam F

Beam G


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-10

-8

-6

-4

-2

0

2

4

6

8

10

0 50 100 150 200

Strain

(10-6)

Load (kN)

Strain VS Load

CH 1

CH 2

-10

-8

-6

-4

-2

0

2

4

6

8

10

0.00 50.00 100.00 150.00

Strain

(10-6)

Load (kN)

Strain VS Load

CH 1

CH 2

-5

-4

-3

-2

-1

0

1

2

3

0.00 50.00 100.00 150.00

Strain

(10-6)

Load (kN)

Strain VS Load

CH 1

CH 2

Beam E Beam F

Beam G


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Conclusion Regarding BeamTest There is a significant increase in shear

carrying capacity when spiral is usedas shear reinforcement

The pitch of the spiral should beselected as greater than (hagg+5)mm


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Experiment 4 & Design

MethodsU. Kaneswaran


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Experiment 4

Dimensions of the slab panel Width =1200mm

Length = 1200mm

Thickness = 150mm

Specimens tested Panel A : no spiral reinforcement

Panel B : with spiral reinforcement


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Reinforcement Arrangement

Panel A

Panel B


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Testing Arrangement


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Failure loadsSlab panel Failure load (kN)

A 262.1

B 299

0

50

100

150

200

250

300

0.00 2.00 4.00 6.00 8.00 10.00

Load

(kN

)

Deflection (mm)

Load VS Deflection

Panel B

Panel A

Strength enhancement in panel B =36.9 kN


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Strain variation in spirals with load for panel B

-400

-200

0

200

400

600

800

1000

0 50 100 150 200 250 300

Strain

()

Load (kN)

@ column face

@ 1.5d away from column face

@ 1.5d away from column face


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Crack pattern

Panel A Panel B


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Conclusion RegardingExperiment 5 There is a significant increase in load

carrying capacity (36.9kN)

Spirals were not yielded under the

direct tension induced on them The deflection of panel B is higher

than panel A at failure


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Design Methods

There are two design methodsavailable to calculate the shearcarrying capacity of spirals

Average integration method

Discrete method


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Average Integration Method

Proposed by Ghee Considers spiral geometry by a factor k =/4


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Discrete Method

Considers the exact variation of spiralcontribution to shear force due tospiral geometry


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Arrangement of Spiral and FailureSurface

Beam D

Beam E

Beam G


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Expected Results VS ActualResults Average integration method

Beam Expectedenhancement (kN)

Actualenhancement (kN)

E 32.31 39.24F 25.17 29.43G 15.85 17.66

The actual enhancement is higher than the expected shearenhancement


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Expected Results VS ActualResults Discrete method

Beam Expectedenhancement (kN)

Actualenhancement (kN)

E 50.53 39.24F 38.59 29.43G 24.50 17.66

The expected shear enhancement is higher then the actualshear enhancement


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Conclusion Regarding AvailableDesign Methods

The actual shear enhancement is closer tothe expected shear enhancementcalculated using average integration

method In the average integration method the

actual contribution from the spiral geometryis not considered

More specimens has to be tested withdifferent diameter of spirals to identify thebest method to calculate the shear

enhancement of spirals


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Future works to be done

Find the anchorage length of differentdiameter of spirals

Test different sizes of beams with

different diameter of spirals anddifferent pitches

Test the slab panel with different

arrangement of spirals


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Thank you

Documents

Strength Enhancement in Concrete Confined by Spirals