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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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Experimental Results cont..
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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Experimental Results cont..
-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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Experimental Results
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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Experimental Results cont..
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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Experimental Results cont..
-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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Experimental Results
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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Experimental Results cont..
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