post tensioned concrete floors amr abdelrahman ain shams
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POST-TENSIONEDCONCRETE FLOORS
Dr. Amr Abdelrahman Associate Professor, Ain Shams University, Cairo, Egypt
April 2006
Why post-tensioning?Structural Systems of Slabs
RC solid slabs on beams
Ribbed slabs (hollow blocks, waffle)
RC flat slabs
Hollow core precast slabs
Post-tensioning Can Provide
Faster construction
Durable structureBetter connections compared
to precast slabs
“Cheaper” alternative
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How can we do it?normalreinforcement
tendons
middlestrip
column
stripmiddlestrip
middlestrip
middlestrip
columnstrip
middlestrip
middlestrip
columnstrip
100% banded through columnsin both directions and normal reinforcement
100% banded through columns in one directionand uniform distribution in other direction
75% concentrated in column strip and25% in middle strip in both directions
75% concentrated in column strip and 25% i nmiddle strip in one direction-other direction uniform
Post-tensioned
flat slabs
Choice of the
system:
•Aspect ratio•Constructibility issues
Analysis?
Equivalent frame method
Finite element method
SAP2000
Computer programs for prestressedconcrete members “ADAPT, Concise, ….”
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Structural analysisEquivalent frame method
Aalami et al. 2001
Cable layout
Banded tendons Distributed tendons
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Computer model
L
L(1-2 ) L
2 31 4 5 e5e1e3
Curve(1) Curve (2)
Curve(3)
L
Rcolumn
yi =
aix
i2 + b
ix
i+ c
i(1)
y1 = e1 ( fo r c urve 1) (2)
y3 = e3 ( fo r c urve 2) (3)
y5 = e5 ( fo r c urve 3) (4)
y2 (for curve 1) = y2 (for curve 2) (5)
y4 (for curve 2) = y4 (for curve 3) (6)
2curvefordx
dy 1curvefor
dx
dy
22
⎟ ⎠
⎞⎜⎝
⎛ =⎟
⎠
⎞⎜⎝
⎛
3curvefordx
dy 2curvefor
dx
dy
44
⎟ ⎠
⎞⎜⎝
⎛ =⎟
⎠
⎞⎜⎝
⎛
1)curve(for0dxdy =⎟
⎠ ⎞⎜
⎝ ⎛
1
3)curve(for0dx
dy=⎟
⎠
⎞⎜⎝
⎛
5
(7)
(8)
(9)
(10)
Computer model
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SPECIMENS
Pattern No1
L y
Lx
L y
Lx
L y
Lx
L y
Lx
Pattern No2
Pattern No3 Pattern No4
The analyzed panels are
divided into three groups
according to its aspect ratio.
The applied aspect ratios in
analysis are 1.00, 1.33, and 2.00.
For plates with aspect ratio 1.33
and 2.00 “Lx” represent the
long direction and “Ly” is the
short direction.
Analysis of PT flat slabs
Test specimensPlate
Dimensions Pattern PT Force (kN)
Lx(m) Ly(m) ts(m) Px Py
1 12.50 x 12.50 12.50 12.50 0.30 1 1150 1150
2 12.50 x 12.50 12.50 12.50 0.30 2 1400 1400
3 12.50 x 12.50 12.50 12.50 0.30 3 1350 1350
4 12.50 x 12.50 12.50 12.50 0.30 4 1300 1300
5 10.0 x 10.0 10.00 10.00 0.24 1 600 600
6 10.0 x 10.0 10.00 10.00 0.24 2 950 950
7 10.0 x 10.0 10.00 10.00 0.24 3 700 700
8 10.0 x 10.0 10.00 10.00 0.24 4 700 700
9 7.50 x 7.50 7.50 7.50 0.18 1 300 300
10 7.50 x 7.50 7.50 7.50 0.18 2 350 350
11 7.50 x 7.50 7.50 7.50 0.18 3 350 350
12 7.50 x 7.50 7.50 7.50 0.18 4 350 35013 10.0 x 7.50 10.00 7.50 0.24 1 437.5 350
14 10.0 x 7.50 10.00 7.50 0.24 2 625 500
15 10.0 x 7.50 10.00 7.50 0.24 3 500 400
16 10.0 x 7.50 10.00 7.50 0.24 4 500 400
17 10.0 x 5.0 10.00 5.00 0.24 1 210 368
18 10.0 x 5.0 10.00 5.00 0.24 2 210 368
19 10.0 x 5.0 10.00 5.00 0.24 3 210 368
20 10.0 x5.00 10.00 5.00 0.24 4 210 368
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0
50
100
150
200
250
300
350
12 . 5 x 12 . 5 10 . 0 x 10. 0 7. 50 x 7. 50
Slab dimensions
C o s t p e r m 2 ( E G P )
Pattern 1
Pattern 2
Pattern 3
Pattern 4
Effect of tendon patterns
Plates with aspect ratio “1”
Concrete 250 EGP/m3
Non PS steel 3500 EGP/ton
PS steel 16000 EGP/ton
0
50
100
150
200
250
10 . 0 x 7 . 50 10 . 0 x 5 . 00
Slab dimensions
C o s t p e r m 2 E G P
Pattern 1
Pattern 2
Pattern 3
Pattern 4
Plates with aspect ratio “1.33 and 2”
Effect of tendon patterns
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0
50
100
150
200
250
300
56 .25 100 156 .25
PT Plate Area
C o s t p e r m 2 ( E G P )
Effect of PT plate area
0
50
100
150
200
250
300
5.0x10.0 7.50x10.0 10.0x10.0
Plates with different aspect ratios
C o
s t p e r m 2 E G P
0
50
100
150
200
250
300
7.50 x7 .50 10 .0x10 .0 12 .50 x12 .50
Plates with aspect ratio “1”
PT slabs
RC slabs
PT vs. RC slabs
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Case study I
8 x 5. 4 = 4 3.
25 8 .5 6
115.40
5 9 . 4
0
55.67
PART 1 PART 3
PART 2
Plan of the first basement framing plan
Office Building
Smart Village
2B
1B
G
1st
2nd
3rd
roof
Elevation
E x p a n s i o n j o i n t E x p a n s i o n j o
i n t
E x p a n s i o n
j o i n t
E x p a
n s i o n j o i n t
Overview “Case study I”
Part 3
Part 1
Part 2
Autocad
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Construction sequence “Case study I”
Form Work
Laying Ducts
Profile of Ducts
Cable layout “Case study I”
Ba nded te ndo ns
D is t r i b u ted te ndo ns
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Concreting “Case study I”
Measurements “Case study I”
Stressing
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Construction details “Case study I”
Jacking
end
regions not prestressed in direction parallel to tendons
tendons
free edge
Flat duct
Dead
end
Formwork removal “Case study I”
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Grouting “Case study I”
What if it was RC ? “Case study I”
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Does it look good? “Case study I”
Front elevation
Sideelevation
1 5 % c o s t s
a v i n g
Case study II
14.9017.0017.0011.00
59.90
1 0 . 9
1 6 . 0
1 3 . 6
4 0 . 5
Main beam
Main beam
s e c o n d a r y b e a m s
Exhibition Hall, Nasr City
opening
prestressed
non-prestressed
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Details “Case study II”
1500
1100
Main beam
400
700
160
Secondary beam
Details “Case study II”
Frame
Bending moment
Deformed shape after stressing