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

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

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

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

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

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.

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

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

M cr(t) = (1 – e - (t) ) (M II – M I ) M Final(t) = M II + (M I – M II ) e - (t) where: (t) = creep factor at time t e = Base of Napierian logarithms = M I = Movement due to permanent loads before change of statical system M II = Movement due to the same loads applied on changed statical system (build on false-work)

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

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

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

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

In-span Hinge Mid-span Hinge Bearing & Expansion Joint Bearing

Old Generation of Midspan Hinge (not recommended)

Active Hinge (proposed by Jean M. Muller)

Mid-span Hinge with Strong Back

Expansion Joint at Abutment Abutment Span 1

Over Extended of Bearing Top Plate

Torsional Creep Deformation in Horizontally Curved Bridge

Introduction Understanding of Creep & Shrinkage Code Development of Creep & Shrinkage Impact of Creep & Shrinkage on Post-Tensioned Bridges 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