civil engineering

1. VIRGINIA CONCRETE
CONFERENCE
March 3-4, 2011
Presented by:
Teddy Theryo, P.E.
Parsons Brinckerhoff
SEGMENTAL BRIDGE GROUP

2. 1. Introduction
2. Understanding of Creep & Shrinkage
3. Code Development of Creep & Shrinkage
4. Impact of Creep & Shrinkage on Post-Tensioned
Bridges
5. Conclusions

3. Definitions
 Creep is time dependent deformations of concrete
under permanent loads (self weight), PT forces and
permanent displacement
 Shrinkage is shortening of concrete due to drying and
is independent of applied loads

4. Factors Affecting Creep
 Concrete mix proportion
 Cement properties
 Curing conditions
 Size and shape of members
 Environment
 Age at loading
 Stress level

5. Factors Affecting Shrinkage
 Concrete mix proportion
 Cement properties
 Aggregate properties
 Curing conditions
 Size and shape of members
 Environment

6.  In structural concrete creep and shrinkage strains are
coexist and occur together.
 The rate of both creep and shrinkage decrease with time.
 Theoretically the creep and shrinkage are considered
diminished at 10,000 days (27 years) after construction.
 For practical purposes the ending time of 4,000 days (11
years) is also commonly used in creep and shrinkage
calculations .
 Mathematically the non linear shape of creep and
shrinkage has been assumed as hyperbolic, exponential or
logarithmic.

7. Strain
Strain
Time Time
Creep strain
Instantaneous
strain
TYPICAL CREEP – TIMECURVE TYPICAL SHRINKAGE – TIMECURVE

8. Drying
creep
Basic
creep
Total
creep
Shrinkage
Nominal
elastic strain
Time (t – t )
0
t0
Strain

9. 0 50 100 150 200
Instantaneous
recovery
Creep recovery
Residual
deformation
500
1000
1500
Strain on application
of load
Time since application of load - days
Strain
-
10
-
6

10. 1. Introduction
2. Understanding of Creep & Shrinkage
3. Code Development of Creep & Shrinkage
4. Impact of Creep & Shrinkage on Post-Tensioned
Bridges
5. Conclusions

11. Relationship between creep and elastic deformations
cr = el =
E28
where: cr = creep strain
el = elastic strain
= stress
E28 = elastic modules of concrete at age 28 days
= creep factor

12. 4.0
3.5
3.0
2.5
2.0
1.5
3.72
3.03
2.57
2.22
2.00
1.70
1.44
1.0
0.5
0 3 7 14 21 28 42 56 3 4 5 6 9 1 1.5 2 3 5
Days Months Years
1.20
1.07
1.00
0.96
0.91
0.94
0.90
0.88
t
DURATION OF LOADING
TOTAL
ELASTIC
AND
CREEP
STRAIN

13. Mcr(t) = (1 – e - (t)) (MII – MI)
MFinal(t) = MII + (MI – MII) e- (t)
where: (t) = creep factor at time t
e = Base of Napierian logarithms
= 2.7182
MI = Movement due to permanent loads before
change of statical system
MII = Movement due to the same loads applied on
changed statical system (build on
false-work)

15. Free Cantilever Statical System
Changed Statical System (Midspan Continuous)
MFinal (t)
½L ½L
MI M =
I
Fixed Fixed
q
qL
2
8
MII
M =
II
qL
2
12
qL
2
24
MII
MI
Mcr (t)

16. el (t )
0
cr (t )
P P
Pef Pef
Cantilever Beam
Simple Beam
el ( )
t0
cr (t )

17. P
Post-Tensioned Beam
P
P P
P
ef P
ef
el (t )
0
el (t )
0
el (t )
PT Tendon

20. 1. Introduction
2. Understanding of Creep & Shrinkage
3. Code Development of Creep & Shrinkage
4. Impact of Creep & Shrinkage on Post-Tensioned
Bridges
5. Conclusions

21. CEB-FIP 1970 Model Code
CEB-FIP 1978 Model Code
CEB-FIP 1990 Model Code
FIB 2010 Draft Model Code
ACI-209
BP3

22. 1. Introduction
2. Understanding of Creep & Shrinkage
3. Code Development of Creep & Shrinkage
4. Impact of Creep & Shrinkage on Post-Tensioned
Bridges
5. Conclusions

23. There are two major impacts of creep and shrinkage
on structural concrete
 Deformations (simply supported and indeterminate
structures)
 Redistribution of stresses / forces on indeterminate
structure, including support reactions

24. C
L
C
L
In-span Hinge
In-span Hinge
Mid-span Hinge
Bearing &
Expansion Joint Bearing

25. Expansion Joint
Bearing
Old Generation of Midspan Hinge
(not recommended)

26. Mid-Span
Hinge
In-Span
Hinge
5.1%
S
1.8%
2.5
5.0
7.5
Deformation
(cm)
Span Length: 79m (260 feet)

27. Deck Profile based
on As-Built Dwgs
Existing
Deck Profile
Reference
Line
C EXP. JT. NO. 3
L
STA. 67+16.50
C PIER 9
L
STA. 68+16.59
BEGIN S.E. TRANSITION
STA. 68+18
C PIER 8
L
STA. 65+74
0.36’
0.46’
0.82’

28. Deck Profile based
on As-Built Dwgs
Existing
Deck Profile
Line
C EXP. JT. NO. 3
L
STA. 67+16.50
C PIER 9
L
STA. 68+16.59
C PIER 8
L
STA. 65+74
0.49’
0.35’
0.84’
Reference

29. Active Hinge
(proposed by Jean M. Muller)
Active hinge member
Midspan expansion joint
Typical internal
diaphragm
Hydraulic jack

30. Sliding
Expansion Joint
C
L Mid-Span
Steel Strong Back
Fixed
Elastomeric Bearing
Teflon Surface (typ)
Mid-span Hinge with Strong Back

31. -0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 200 400 600 800
Distance Along the Bridge (ft)
Vertical
Displacement
(in)
L
L
@ TF
o
creep
0.079 Degree 8’-6”
3’-6”
12’-0”
L creep = 0.079 x 3.5 x 12 = 3.31”
Assuming 50% of the creep had been corrected
camber during segment casting.
L available gap at 60F in 2010
o
Abutment 1 = 3-3/4” - 0.5 (3.31) = 2.09” vs 1.75”
Abutment 29 = 3-3/8” - 0.5 (3.31) = 1.75” vs 1”
Point of rotation
creep
V
Abutment
Back Wall
Camber Diagram of Unit 1 at T =
End Span Girder Rotation at Abutment 1
(Varina-Enon Bridge Case Study)
Elastomeric Bearing

32. Expansion Joint at Abutment
Abutment
Span 1

33. X C
L
Top Plate
Bottom Pot
>X
C
L Top Plate
X min.
C
L
C
L Bottom
Pot
C
L Bottom
Pot
creep at T =
Top Plate
creep at T =
e =
Ideal/preferred
position at T=
Incorrect
position at T=
Correct bearing &
joint expansion
preset at construction
Expansion
Joint

34. Over Extended of Bearing Top Plate

35. Torsional Creep Deformation in Horizontally Curved Bridge
A
A
GOOD
BAD
Roadway Axis
Girder Axis
Support
Axis
SECTION A-A
BAD STRATEGY GOOD STRATEGY
Top Abutment
Elevation

36.  Introduction
 Understanding of Creep & Shrinkage
 Code Development of Creep & Shrinkage
 Impact of Creep & Shrinkage on Post-Tensioned
Bridges
 Conclusions

37. In order to avoid the negative impacts of long-term
creep and shrinkage:
1. Good understanding of creep and shrinkage behaviors
2. Accurate estimation of creep and shrinkage on structural
concrete design
3. Proper counter measures of long-term creep and
shrinkage effects
4. Implement simple structural details