gt strudl users group 22 nd annual meeting & training seminar june 24, 2010
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GT STRUDL Users Group 22 nd Annual Meeting & Training Seminar June 24, 2010. Practical Modeling Technique for Transfer Length Chris Carroll, Ph.D. Assistant Professor Department of Civil Engineering University of Louisiana at Lafayette. Overview. Introduction. Background. - PowerPoint PPT PresentationTRANSCRIPT
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GT STRUDL GT STRUDL Users Group22nd Annual Meeting & Training
SeminarJune 24, 2010
Practical Modeling Technique for Transfer Length
Chris Carroll, Ph.D.
Assistant Professor
Department of Civil Engineering
University of Louisiana at Lafayette
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Overview
Introduction
Top-strand Effect
Test Speciemens
GT STRUDL Model
Background
Practical Modeling Techniquefor Transfer Length
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BackgroundDevelopment length (standard reinforcing steel)
• The length required to anchor the reinforcing to fully develop the stress in the reinforcing at the nominal moment capacity of the member (AASHTO)• The length of embedment required to prevent slip between reinforcing and the surrounding concrete when that reinforcing is placed in tension (or
compression)
Practical Modeling Technique
for Transfer Length
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Background
'
3
40 b tr
b
y t e sd bc K
dc
fL d
f
Required stress in steel
Concrete Strength
Location of the bar Coating of the bar
Size of the bar
Diameter of the bar
Cover and confinement
Effect of lightweight concrete
Required stress in steel
Diameter of the bar
Development length (standard reinforcing steel)
Practical Modeling Technique for Transfer Length
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Background
Development Length• The length required to
anchor the strand to fully develop the stress in the strand at the nominal moment capacity of a member
3000 1000ps sese
d b b
f ffL d d
Lt Lfb
fse
fps
Ld
2
3d ps se bL f f d
ACI
AASHTO
Practical Modeling Technique for Transfer Length
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BackgroundTransfer Length• The bonded length of
strand required to transfer the prestress force in the strand to the surrounding concrete
3000 1000ps sese
d b b
f ffL d d
Lt = 50db
Lt = 60db
3000se
t b
fL d
Lt
fseACI
AASHTO
Practical Modeling Technique for Transfer Length
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Unconservative
BackgroundTransfer Length (Code Provisions)
UnconservativeUnconservative
Practical Modeling Technique for Transfer Length
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Practical Modeling Techniquefor Transfer Length
Background
Top-strand Effect
> 12”
Deformed Bar
• Provisions exist for development length of deformed bars
• Ld multiplied by 1.3 (ACI) and 1.4 (AASHTO) with > 12 inches of fresh concrete below the bar
• Provisions do not exist for the development or transfer length of prestressing strands
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Practical Modeling Techniquefor Transfer Length
BackgroundTop-strand Effect
a
b
a
b
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Practical Modeling Techniquefor Transfer Length
Background
Top-strand Effect– Is top-strand effect a factor of the amount of
concrete beneath the strand?– New hypothesis: Top-strand effect may be a factor
of the amount of concrete above the strand rather than the amount below or a combination thereof
12 ft 12 ft
Block A Block B
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Practical Modeling Techniquefor Transfer Length
Test SpeciemensT-beams
30 in.
4 in.
5 in.
24 in.
2 in.
8 in.
Large
3 in.
19 in.
2 in.
4 in.
24 in.
Medium
8 in.
24 in.
2 in.
17 in.
2 in.
4 in.
Small
8 in.
½” regular ½” special 0.6”
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Practical Modeling Techniquefor Transfer Length
Test Specimens
300 ksi
270 ksi
Normal InvertedA
A
B
B
Normal
Inverted
Normal
Inverted
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Practical Modeling Techniquefor Transfer Length
Test SpecimensT-beams
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Practical Modeling Techniquefor Transfer Length
Test SpecimensTop-strand blocks
12 ft 12 ft
Block A Block B
24”
4”
2”
5”
5”
5”
5”
2”
2”
5”
5”
2”
14”
4”
A
B
CC
D
E
F
G
H
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Practical Modeling Techniquefor Transfer Length
Test SpecimensTop-strand blocks
Single Strand Blocks
Five Strand Blocks
Three Strand Blocks
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Practical Modeling Techniquefor Transfer Length
Test SpecimensTop-strand blocks
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Practical Modeling Techniquefor Transfer Length
Test SpecimensTop-strand blocks
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Practical Modeling Techniquefor Transfer Length
Test SpecimensTop-strand blocks
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Practical Modeling Techniquefor Transfer Length
Test SpecimensTransfer Length
50 mmspacing
100 mmspacing
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Practical Modeling Techniquefor Transfer Length
Test SpecimensTransfer Length
50 mmspacing
100 mmspacing
≈ 30,000 measurements
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Practical Modeling Techniquefor Transfer Length
Test SpecimenTransfer Length
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Practical Modeling Techniquefor Transfer Length
Test SpecimensBond/Shear Failure
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Practical Modeling Techniquefor Transfer Length
Test SpecimensBond/Shear Failure
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Practical Modeling Techniquefor Transfer Length
Test SpecimensBond/Shear Failure
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Practical Modeling Techniquefor Transfer Length
Test SpecimensBond/Shear Failure
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Practical Modeling Techniquefor Transfer Length
Test SpecimensBond/Shear Failure
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Practical Modeling Techniquefor Transfer Length
Test SpecimensBond/Shear Failure
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Practical Modeling Techniquefor Transfer Length
Top-strand EffectTransfer Length• Influence of Release Method• Influence of Strand Strength• Influence of Strand Diameter/Area• Influence of Effective Prestress• Influence of Concrete Strength• Influence of Time• Influence of Casting Orientation• Proposed Transfer Length Equation
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Practical Modeling Techniquefor Transfer Length
Top-strand EffectTransfer Length (Influence of Casting Orientation)
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Practical Modeling Techniquefor Transfer Length
Top-strand EffectTransfer Length (Influence of Casting Orientation)
Amount of Concrete Below
Amount of Concrete Above
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Practical Modeling Techniquefor Transfer Length
Top-strand EffectTransfer Length (Influence of Casting Orientation)
Same Amount of Concrete Below
Same Amount of Concrete Above
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Practical Modeling Techniquefor Transfer Length
Amount of Concrete Above
Amount of Concrete Below
Top-strand EffectTransfer Length (Influence of Casting Orientation)
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Practical Modeling Techniquefor Transfer Length
Top-strand EffectTransfer Length (Proposed Transfer Length Eq.)
'
sib
ci
fX d
f
12 in.
24castd 24castd 0castd
1
Z
Tra
nsfe
r Le
ngth
A B
C
Amount of Concrete Above the Strand
'
sib
ci
fX d
f
12 in.
24castd 24castd 0castd
1
Z
Tra
nsfe
r Le
ngth
A B
C
Amount of Concrete Above the Strand
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Practical Modeling Techniquefor Transfer Length
Top-strand EffectTransfer Length (Proposed Transfer Length Eq.)
2'
2435
40castsi
t b
c
dfL d
f
= 1 = 2
R2 = 0.176R2 = 0.206
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Practical Modeling Techniquefor Transfer Length
Top-strand EffectTransfer Length (End-slip)
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Practical Modeling Techniquefor Transfer Length
Top-strand Effect
Conclusions
• Top-strand effect was more dependent on the amount of concrete cast above the strand
• On average Lt increased ½ in. for every 1 in. reduction in the amount of concrete cast above the strand
2'
2435
40castsi
t b
ci
dfL d
f
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
$$===================================================$$ CONCRETE ELEMENT DATA$$===================================================
TYPE PLANE STRESSGENERATE 6 ELEMENTS ID 'AB-1', 1 FROM 'A1',1 TO 'A2',1 TO 'B2',1 TO 'B1',1GENERATE 6 ELEMENTS ID 'BC-1', 1 FROM 'B1',1 TO 'B2',1 TO 'C2',1 TO 'C1',1
ELEMENT PROPERTIES TYPE 'IPLQ' THICK 4'AB-1' TO 'AB-6''BC-1' TO 'BC-6‘
CONSTANTS E 3949 -'AB-1' TO 'AB-6‘ –'BC-1' TO 'BC-6‘
G 1688 -'AB-1' TO 'AB-6' -'BC-1' TO 'BC-6‘
POI 0.17 -'AB-1' TO 'AB-6' -'BC-1' TO 'BC-6'
A1 A2 A3 A4 A5 A6 A7
C1 C2 C3 C4 C5 C6 C7
B1 B2 B3 B4 B5 B6 B7
AB-1 AB-2 AB-3 AB-4 AB-5 AB-6
BC-1 BC-2 BC-3 BC-4 BC-5 BC-6
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
$$==================================================================$$ SPECIFY JOINT COORDINATES$$==================================================================
GENERATE 5 JOINTS ID 'C1',1 X 0. -DIFF -1 2 AT 1 2 AT 2. Y 2. Z 0.
C1 C2 C3 C4 C5
(-1,2) (0,2) (1,2) (3,2) (5,2)
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
$$==================================================================$$ SPECIFY STRAND PROPERTIES $$==================================================================
TYPE PLANE TRUSSGENERATE 4 MEMBERS ID 'STRND-0',1 FROM 'Cd0', 1 TO 'Cd1'
MEMBER PROPERTIES PRISMATIC AX 0.153'STRND-0' TO 'STRND-3'
Cd0 Cd1 Cd2 Cd3 Cd4
STRND-0 STRND-1 STRND-2 STRND-3
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
$$===================================================$$ SPECIFY BOND ELEMENT PROPERTIES$$===================================================
ELEMENT INC'BOND-1' 'Cd1' 'C1''BOND-2' 'Cd2' 'C2''BOND-3' 'Cd3' 'C3''BOND-4' 'Cd4' 'C4'
NONLINEAR SPRING PROPERTIESCURVE 'BOND' FORCE VS DISPL0.0 0.0 -50.0 -1.0END
ELEMENT PROPS'BOND-1' TO 'BOND-4' TYPE 'NLS'
NONLINEAR SPRING ELEMENT DATASTIFFNESS'BOND-1' TO 'BOND-4' X CURVE 'BOND'END
50 kip/in.
100 kip/in.
150 kip/in.
200 kip/in.
250 kip/in.
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
61100 6.5 10 28500 0.153 31.2
P A EA
T
P T EA
P x
$$==================================================================$$ SPECIFY TEMPERATURE LOADINGS$$==================================================================
LOADING 'TRANSFER' '-1100 TEMPERATURE CHANGE'MEMBER TEMPERATURE LOADS'STRND-0' TO 'STRND-3' AXIAL -1100
Cd0 Cd1 Cd2 Cd3 Cd4
STRND-0 STRND-1 STRND-2 STRND-3
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model• 4x4 in. 12 ft concrete prism (k = 50 kip/in.)
• 4x4 in. 12 ft concrete prism (k = 50 kip/in.)
• 4x4 in. 12 ft concrete prism (k = 250 kip/in.)
• Excel Spreadsheet
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
99% max force
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
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Practical Modeling Techniquefor Transfer Length
GT STRUDL Model
• 4x24 in. 12 ft concrete block (k = variable)
• 17 in. deep T-beam with eccentric strands
• 17 in. deep T-beam with eccentric strands
• 8 ft deep 96 ft long I-beam (End-zone)
• 8 ft deep 96 ft long I-beam (End-zone)
???Questions