Prestressed Concrete

Module aims

  • To introduce the fundamental principles about the structural behaviour and design criteria of Prestressed Concrete Structures.
  • To introduce the fundamental mechanics to define the internal forces.
  • To review the current technology available to prestress concrete structures.
  • To introduce the formulae to estimate the initial and time-dependent losses.
  • To emphasis the fundamentals but reference is made to Eurocode 2.
  • To present the serviceability limit states that are critical for the design of conventional prestressed concrete structures and the inequalities to fulfil such limit states are derived, allowing the prestressing force and its eccentricity to be determined.
  • To cover the specific implications for the ultimate limit states.

Learning outcomes

On successfully completing this course unit, students will be able to:

  •  Obtain the internal forces due to the prestressing in a prestressed concrete structure, being able to identify the primary and secondary components of the total internal forces.
  • Evaluate the initial and time-dependent losses.
  • Propose an appropriate system to prestress a particular structure.
  • Design the prestressing layout and the prestressing force that fulfils the relevant limit states.

Module syllabus

  • Concept of prestressing (historical approach, and prestressing types).
  • Structural analysis of prestressed statically determinate structures including: Anchorage and deviating forces introduced by the tendons; Internal forces and strains due to prestressing; Tendon centroid, and prestressing layouts; Mechanical properties before and after grouting; Introduction of self-weight during prestressing in post-tensioned structures; Introduction of lateral bending during prestressing in post-tensioned structures.
  • Structural analysis of prestressed statically indeterminate structures including: methods for the analysis of prestressed statically indeterminate structures: Primary, secondary and total internal forces due to prestressing.
  • Prestressing technology including: Steel products and technologies for prestressing (strands, tendons, bars); Anchorage systems, ducts, couplers; Technological requirements for the prestessing layouts; Threading, prestressing, and grouting; External prestressing technology.
  • Prestressing losses: Concept of loss and classification of losses (initial and long-term losses); Frictional losses; Elastic shortening losses; Anchorage drawn-in losses and transmission lengths; Prestressing strategies; Prestressing losses due to concrete creep, concrete shrinkage and steel relaxation.
  • Serviceability limit state including: SLS of normal tension stresses (decompression, cracking, and crack opening limit states); SLS of normal compression stresses; SLS deformation, SLS vibration; Prestressing approaches and classes.
  • Design of prestressed structures: Central kern; Inequality equations for the design of prestressed concrete structures; Magnel diagrams; Regions where the centroid of the prestressing layout has to be located; Relation between section efficiency and amount of prestressing.
  • Specific implications for ultimate limit states.
  • Anchorage zones.
  • Prestressed concrete slabs. 

No.

Topic

Staff

01

Concept of prestressing. Historical approach

Different types of prestressing

Prestressing by tendons

Prestressing types according to the moment in which the prestressing is applied

Prestressing types according to the location of the tendons in relation to the concrete section

Prestressed tie (including examples)

ART

02

Structural analysis of prestressed statically determinate structures

Anchorage and deviating forces introduced by the tendons

Internal forces due to prestressing in statically determinate structures

Strains due to prestressing

Prestressing of in-situ concrete beams (post-tension)

Tendon centroid            

Prestressing of precast concrete beams (pre-tension).

Prestressing layouts

Mechanical properties before and after grouting

Introduction of self-weight during prestressing in post-tensioned structures

Introduction of lateral bending during prestressing in post-tensioned structures

Example

ART

03

Structural analysis of prestressed statically indeterminate structures

Methods for the analysis of prestressed statically indeterminate structures

Static internal forces due to prestressing; Secondary internal forces due to prestressing; and Total internal forces due to prestressing

Examples

ART

04

Prestressing technology

Steel products and technologies for prestressing (strands, tendons, bars)

Mechanical properties of steel products

Anchorage systems. Types

Ducts

Couplers

Prestessing layout

Introduction of prestressing elements, prestressing, Grouting

Jacks

External prestressing technology

ART

05

Prestressing losses

Concept of loss

Classification of losses (initial and long-term losses)

Initial Prestressing losses

Frictional looses

Elastic shortening losses

Anchorage drawn-in losses

Transmission lengths

Initial internal forces due to prestressing

Prestressing strategies

Examples

ART

06

Long-term Prestressing losses

Historical introduction

Concrete creep and shrinkage

Steel relaxation

Prestressing losses due to concrete creep, concrete shrinkage and steel relaxation

Example

Coursework is set

ART

07

Serviceability limit state.

SLS of normal tension stresses (decompression, cracking, and crack opening limit states)

SLS of normal compression stresses

SLS deformation, SLS vibration

Prestressing approaches and classes

Tutorial (Coursework)

ART

08

Design of prestressed structures

Central kern

Inequality equations for the design of prestressed concrete structures

Magnel diagrams

Regions where the centroid of the prestressing layout has to be located

Relation between section efficiency and amount of prestressing

Examples

Ultimate limit states

Ultimate limit state of normal stresses

Example

Ultimate limit state of shear stresses

Coursework submission

ART

09

Anchorage zones

Prestressed concrete slabs

Course work feedback

ART

10

Revision

ART

Teaching methods

A combination of lectures and tutorials. 

Assessments

Assessment will be 75% written examination and 25% coursework (MSc)/100% written examination (UG). 

Reading list

Module leaders

Dr Ana Ruiz-Teran