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LONG-TERM EFFECT OF CREEP & SHRINKAGE ON SEGMENTAL CONCRETE BRIDGES

VIRGINIA CONCRETE

CONFERENCEMarch 3-4, 2011

Presented by:

Teddy Theryo, P.E.

Parsons Brinckerhoff SEGMENTAL BRIDGE GROUP

Presentation Outline

1. Introduction2. Understanding of Creep & Shrinkage3. Code Development of Creep & Shrinkage4. Impact of Creep & Shrinkage on Post-

Tensioned Bridges5. Conclusions

Introduction

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

Introduction

Factors Affecting Creep

Concrete mix proportionCement propertiesCuring conditionsSize and shape of membersEnvironmentAge at loadingStress level

Introduction

Factors Affecting Shrinkage

Concrete mix proportionCement propertiesAggregate propertiesCuring conditionsSize and shape of membersEnvironment

Introduction 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.

Creep and Shrinkage Typical Time Curve

S tr a

in

S tr a

in

Time Time

Creep strain

Instantaneous strain

TYPICAL CREEP – TIMECURVE TYPICAL SHRINKAGE – TIMECURVE

Drying creepBasic creep

Totalcreep

Shrinkage

Nominalelastic strain

Time (t – t )0t0

Stra

i n

0 50 100 150 200

Instantaneousrecovery

Creep recoveryResidualdeformation

500

1000

1500

Strain on applicationof load

Time since application of load - days

Stra

in -

10-6

Creep Analysis Fundamental

Relationship between creep and elastic deformations cr = el

= E28

where: cr = creep strain el = elastic strain = stressE28 = elastic modules of concrete at age 28 days

= creep factor

4.0

3.5

3.0

2.5

2.0

1.5

7 days

14 days

28 days56 days

3 months

6 months

1 year

3.72

3.03

2.57

2.222.00

1.701.44

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

TOTA

L EL

AST

IC A

ND C

REE P

ST R

AIN

Franz Dischinger Theory on Creep Formulation

Mcr(t) = (1 – e - (t)) (MII – MI)

MFinal(t) = MII + (MI – MII) e- (t)

where: (t) = creep factor at time te = Base of Napierian logarithms = 2.7182

MI = Movement due to permanent loads before change of statical systemMII = Movement due to the same loads applied on changed statical system (build on false-work)

Variation of Creep Factors

Moment due to Creep

Free Cantilever Statical System

Changed Statical System (Midspan Continuous)

MFinal (t)

½L ½L

MI M = I

Fixed Fixedq

qL2

8

MII M = II qL2

12qL2

24

MII

MIMcr (t)

Structural Concrete subjected to Creep

el (t )0

cr (t )

P P

Pef Pef

Cantilever Beam

Simple Beam

el ( )t 0cr (t )

Structural Concrete subjected to Creep

PPost-Tensioned Beam

P

P P

Pef Pef

el (t )0

el (t )0el (t )

PT Tendon

Creep Moment Development

Moment Distribution Due to Creep

Code Development of Creep & Shrinkage

CEB-FIP 1970 Model CodeCEB-FIP 1978 Model CodeCEB-FIP 1990 Model CodeFIB 2010 Draft Model CodeACI-209BP3

Impact of Creep & Shrinkage on PT Bridges

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

CL

CLIn-span HingeIn-span Hinge

Mid-span HingeBearing & Expansion Joint Bearing

Expansion Joint

Bearing

Old Generation of Midspan Hinge(not recommended)

Effect of Hinge Location on Deformation for Oleron Viaduct (Mathivat)

Mi d

- Spa

n H

i nge

I n- S

pan

Hi n

ge5.1%

In-Span Hinge

Without Hinge

1.8%2.5

5.0

7.5Defo

rmat

ion

(cm

)

Span Length: 79m (260 feet)

NBL Bridge – East Face of CurbRobert E. Lee Bridge (Courtesy of VDOT)

Deck Profile basedon As-Built Dwgs

ExistingDeck Profile

ReferenceLine

C EXP. JT. NO. 3LSTA. 67+16.50

C PIER 9LSTA. 68+16.59

BEGIN S.E. TRANSITIONSTA. 68+18

C PIER 8LSTA. 65+74

0.36’

0.46’0.

82’

NBL Bridge – West Face of CurbRobert E. Lee Bridge (Courtesy of VDOT)

Deck Profile basedon As-Built Dwgs

ExistingDeck ProfileLine

C EXP. JT. NO. 3LSTA. 67+16.50

C PIER 9LSTA. 68+16.59

C PIER 8LSTA. 65+74

0.49’

0.35’0.

84’

Reference

Active Midspan Hinge

Active Hinge(proposed by Jean M. Muller)

Active hinge memberMidspan expansion joint

Typical internaldiaphragm

Hydraulic jack

SlidingExpansion Joint

CL Mid-Span

Steel Strong Back

Fixed

Elastomeric Bearing

Teflon Surface (typ)

Mid-span Hinge with Strong Back

-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)

Verti

cal D

ispl

acem

ent (

in)

LL

@ TFo

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 2010o

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 rotationcreepV

AbutmentBack Wall

Camber Diagram of Unit 1 at T =

End Span Girder Rotation at Abutment 1(Varina-Enon Bridge Case Study)

Elastomeric Bearing


Expansion Joint at Abutment

AbutmentSpan 1

Creep Axial Deformation Impact on Bearing & Expansion Joint Set-up

X CL

Top PlateBottom Pot

>X

CL Top Plate

X min.

CL

CL Bottom Pot

CL Bottom Pot

creep at T =

Top Plate

creep at T = e =

Ideal/preferredposition at T=

Incorrectposition at T=

Correct bearing &joint expansionpreset at construction

ExpansionJoint


Over Extended of Bearing Top Plate

Torsional Creep Deformation in Horizontally Curved Bridge

A

A

GOODBAD

Roadway Axis

Girder Axis

Sup

port

Axi

s

SECTION A-A

BAD STRATEGY GOOD STRATEGY

Top AbutmentElevation

Presentation OutlineIntroductionUnderstanding of Creep & ShrinkageCode Development of Creep & ShrinkageImpact of Creep & Shrinkage on Post-

Tensioned BridgesConclusions

Conclusions

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

THANK YOU

Any Questions?

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