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29 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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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


Top
-
strand Effect

Test Speciemens


GT STRUDL Model

Background

Practical Modeling Technique

for Transfer Length

Background

Development 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

Background



'
3
40
b tr
b
y
t e s
d b
c K
d
c
f
L 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

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 1000
ps se
se
d b b
f f
f
L d d

 
 
 
 
 
 
 
L
t

L
fb

f
se

f
ps

L
d

2
3
d ps se b
L f f d

 
 
 
 
ACI

AASHTO

Practical Modeling Technique
for Transfer Length

Background

Transfer Length


The bonded length of
strand required to
transfer the prestress
force in the strand to the
surrounding concrete

3000 1000
ps se
se
d b b
f f
f
L d d

 
 
 
 
 
 
 
L
t

= 50d
b

L
t

= 60d
b

3000
se
t b
f
L d
 

 
 
L
t

f
se

ACI

AASHTO

Practical Modeling Technique
for Transfer Length

Unconservative

Background

Transfer Length
(Code Provisions)

Unconservative

Unconservative

Practical Modeling Technique
for Transfer Length

Practical Modeling Technique

for Transfer Length

Background

Top
-
strand Effect

> 12”

Deformed Bar


Provisions exist for
development length of
deformed bars


L
d

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

Practical Modeling Technique

for Transfer Length

Background

Top
-
strand Effect

a

b

a

b

Practical Modeling Technique

for 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

Practical Modeling Technique

for Transfer Length

Test Speciemens

T
-
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”
f

regular

½”
f

special

0.6”
f

Practical Modeling Technique

for Transfer Length

Test Specimens

300 ksi

270 ksi

Normal

Inverted

A

A

B

B

Normal

Inverted

Normal

Inverted

Practical Modeling Technique

for Transfer Length

Test Specimens

T
-
beams

Practical Modeling Technique

for Transfer Length

Test Specimens

Top
-
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

C

C

D

E

F

G

H

Practical Modeling Technique

for Transfer Length

Test Specimens

Top
-
strand blocks

Single
Strand
Blocks

Five
Strand
Blocks

Three
Strand
Blocks

Practical Modeling Technique

for Transfer Length

Test Specimens

Top
-
strand blocks

Practical Modeling Technique

for Transfer Length

Test Specimens

Top
-
strand blocks

Practical Modeling Technique

for Transfer Length

Test Specimens

Top
-
strand blocks

Practical Modeling Technique

for Transfer Length

Test Specimens

Transfer Length

50 mm

spacing

100 mm

spacing

Practical Modeling Technique

for Transfer Length

Test Specimens

Transfer Length

50 mm

spacing

100 mm

spacing


30,000 measurements

Practical Modeling Technique

for Transfer Length

Test Specimen

Transfer Length

Practical Modeling Technique

for Transfer Length

Test Specimens

Bond/Shear Failure

Practical Modeling Technique

for Transfer Length

Test Specimens

Bond/Shear Failure

Practical Modeling Technique

for Transfer Length

Test Specimens

Bond/Shear Failure

Practical Modeling Technique

for Transfer Length

Test Specimens

Bond/Shear Failure

Practical Modeling Technique

for Transfer Length

Test Specimens

Bond/Shear Failure

Practical Modeling Technique

for Transfer Length

Test Specimens

Bond/Shear Failure

Practical Modeling Technique

for Transfer Length

Top
-
strand Effect

Transfer 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


Practical Modeling Technique

for Transfer Length

Top
-
strand Effect

Transfer Length

(Influence of Casting Orientation)

Practical Modeling Technique

for Transfer Length

Top
-
strand Effect

Transfer Length

(Influence of Casting Orientation)

Amount of Concrete Below

Amount of Concrete Above

Practical Modeling Technique

for Transfer Length

Top
-
strand Effect

Transfer Length

(Influence of Casting Orientation)

Same Amount of Concrete Below

Same Amount of Concrete Above

Practical Modeling Technique

for Transfer Length

Amount of Concrete Above

Amount of Concrete Below

Top
-
strand Effect

Transfer Length

(Influence of Casting Orientation)

Practical Modeling Technique

for Transfer Length

Top
-
strand Effect

Transfer Length

(Proposed Transfer Length Eq.)

'
si
b
ci
f
X d
f
12 in.
24
cast
d

24
cast
d

0
cast
d

1
Z
Transfer Length
A
B
C
Amount of Concrete Above the Strand
'
si
b
ci
f
X d
f
12 in.
24
cast
d

24
cast
d

0
cast
d

1
Z
Transfer Length
A
B
C
Amount of Concrete Above the Strand
Practical Modeling Technique

for Transfer Length

Top
-
strand Effect

Transfer Length

(Proposed Transfer Length Eq.)



2
'
24
35
40
cast
si
t b
c
d
f
L d
f


 


= 1



= 2

R
2

= 0.176

R
2

= 0.206

Practical Modeling Technique

for Transfer Length

Top
-
strand Effect

Transfer Length
(End
-
slip)

Practical Modeling Technique

for Transfer Length

Top
-
strand Effect

Conclusions


Top
-
strand effect was more dependent on
the amount of concrete cast above the
strand


On average
L
t

increased ½ in. for every 1 in.
reduction in the amount of concrete cast
above the strand



2
'
24
35
40
cast
si
t b
ci
d
f
L d
f


 
Practical Modeling Technique

for Transfer Length

GT STRUDL Model

Practical Modeling Technique

for Transfer Length

GT STRUDL Model


Practical Modeling Technique

for Transfer Length

GT STRUDL Model

Practical Modeling Technique

for Transfer Length

GT STRUDL Model

$$===================================================

$$ CONCRETE ELEMENT DATA

$$===================================================


TYPE PLANE STRESS

GENERATE 6 ELEMENTS ID 'AB
-
1', 1 FROM 'A1',1 TO 'A2',1 TO 'B2',1 TO 'B1',1

GENERATE 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

Practical Modeling Technique

for 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)

Practical Modeling Technique

for Transfer Length

GT STRUDL Model

$$==================================================================

$$ SPECIFY STRAND PROPERTIES

$$==================================================================


TYPE PLANE TRUSS

GENERATE 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

Practical Modeling Technique

for 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 PROPERTIES

CURVE 'BOND' FORCE VS DISPL

0.0 0.0
-
50.0
-
1.0

END


ELEMENT PROPS

'BOND
-
1' TO 'BOND
-
4' TYPE 'NLS'


NONLINEAR SPRING ELEMENT DATA

STIFFNESS

'BOND
-
1' TO 'BOND
-
4' X CURVE 'BOND'

END

50 kip/in.

100 kip/in.

150 kip/in.

200 kip/in.

250 kip/in.

Practical Modeling Technique

for Transfer Length

GT STRUDL Model









6
1100 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

Practical Modeling Technique

for 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



Practical Modeling Technique

for Transfer Length

GT STRUDL Model

99% max force

Practical Modeling Technique

for Transfer Length

GT STRUDL Model

Practical Modeling Technique

for Transfer Length

GT STRUDL Model

Practical Modeling Technique

for 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