Pres 230

7/27/2019 Pres 230

1/43

EUROCODES

Workshop - 27-29 November 2006, Varese, Italy

Bu

ildingtheFut

ureintheEur

o-Mediterrane

anArea

Building the Future

POST-TENSIONED SLABS

IN BUILDINGS

Increasing popularity

/versus/

Lack of specific coverage by Euro codesby

Guy A. TABET

LEBANON

7/27/2019 Pres 230

2/43

EUROCODES


Bu

ildingtheFut

ureintheEur

o-Mediterrane

anArea

Building the FuturePost-tensioned

Slabs in Buildings

7/27/2019 Pres 230

3/43

EUROCODES


Bu

ildingtheFut

ureintheEur

o-Mediterrane

anArea

Building the Future

PRINCIPLE

OF POST-TENSIONED

CONCRETE

7/27/2019 Pres 230

4/43

EUROCODES


Bu

ildingtheFut

ureintheEur

o-Mediterrane

anArea

Building the Future

Illustrative example

P

2 P cos

For harped profile

P

Three-span post-tensioned beam

Tendon

P

V

PA

BW

Free-body diagram of a tendon sectionbetween its low point (A) and point of inflection (B)

w =For parabolic shapeL2

8P x sag

7/27/2019 Pres 230

5/43

EUROCODES


Bu

ildingtheFutureintheEur

o-Mediterrane

anArea

Building the Future

WVdVa

P P

Free-body diagram of tendon

Free-body diagram of beam after removal of tendon

Force system between tendon and beam

P

Va W Vd

P

Illustrative example

7/27/2019 Pres 230

6/43

EUROCODES


BuildingtheFutureintheEur

o-Mediterrane

anArea

Building the Future

Benefits of Post-Tensioned slabs

Longer Spans

Flat Soffits

Flexibility of Layout & Services

Deflection & Crack Control

Thinner Slabs

Reduced Storey Height

Lighter Structure

Fast Construction

Cost Saving

7/27/2019 Pres 230

7/43

EUROCODES



o-Mediterrane

anArea

Building the Future

Who Benefits ?

Clients More clearance & More Flexibility

Less Columns, Larger Open Spaces

Architects Easier Internal Planning

More Elegant Structure

Structural Engineers More solutions

Better Structural Performance

Contractors Quicker and Easier Construction

7/27/2019 Pres 230

8/43

EUROCODES



o-Mediterrane

anArea

Building the Future

IN SLABStwo categories of PT systems are used :

Un-bonded system

&

Bonded system

7/27/2019 Pres 230

9/43

EUROCODES



o-Mediterrane

anArea

Building the Future

Single strand coated with corrosion inhibitinggrease and encased in polyethylene sheathing

PT force is transferred to the concrete by the

anchors provided at the ends

Un-bonded Tendons

7/27/2019 Pres 230

10/43

EUROCODES



o-Mediterrane

anArea

Building the Future

7/27/2019 Pres 230

11/43

EUROCODES


BuildingtheFutureintheEuro-MediterraneanArea

Building the Future

Bond is achieved throughout the length of the tendon by a

cementitious matrix called grout PT force along the tendon is a function of the deformation of the

concrete

Flat corrugated duct

Bonded system tendon detail

for beams & slabs

Strand position in a circular duct

Bonded Tendons

7/27/2019 Pres 230

12/43

EUROCODES



Building the Future

7/27/2019 Pres 230

13/43

EUROCODES



Building the FutureStructural Forms

7/27/2019 Pres 230

14/43

7/27/2019 Pres 230

15/43

EUROCODES



Building the Future

Preferred Option Flat Slab

Minimum Thickness

Flat Soffit

Structural Forms

7/27/2019 Pres 230

16/43

EUROCODES



Building the Future

LOAD BALANCING

A comprehensive solution to Post-Tensioning

by T.Y.LinSimple - General Powerful

for analyzing simple & complex PT structures

Principles

Remove the PT tendons from the structure & replace it with all

the forces that it exerts on the structure when in place

Analyze the structure under this given set of

equivalent loads

Design Concept

7/27/2019 Pres 230

17/43

EUROCODES



Building the Future

Load Balancing

Three-span post-tensioned beam

Tendon

W

VdVa

P P

Design Concept

7/27/2019 Pres 230

18/43

EUROCODES


BuildingtheFu

tureintheEuro-MediterraneanArea

Building the Future

Modeling of two way slab system

Methods available :

Equivalent Frame Method Finite Element Method

.

Analysis of the

Structure

7/27/2019 Pres 230

19/43

EUROCODES


B

uildingtheFu


Building the FutureAnalysis of the

Structure

Finite Element Model

Models a whole Floor Actual Tendon Locations

Plane Frame Model Models a single sub-frame

7/27/2019 Pres 230

20/43

EUROCODES


B

uildingtheFu


Building the Future

Most common modeling of gravity loading

and post-tensioning:

Slab systems are modeled as rows of intersecting twodimensional slab frames.

A single story slab frame consists of a line of column supports

bounded by its tributary Floor levels are treated each separately

Equivalent Frame Method

Analysis of the

Structure

7/27/2019 Pres 230

21/43

EUROCODES


B

uildingtheFu


Building the Future

Typical slab frame

Analysis of the

Structure

7/27/2019 Pres 230

22/43

EUROCODES


B

uildingtheFu


Building the Future

STRUCTURE

PERSPECTIVE


7/27/2019 Pres 230

23/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

ELEMENT MESH PLAN


7/27/2019 Pres 230

24/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

BANDED TENDON LAYOUT


7/27/2019 Pres 230

25/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

DISTRIBUTED TENDON LAYOUT


7/27/2019 Pres 230

26/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the FutureFinite Element Model

TOP FIBER STRESSES

7/27/2019 Pres 230

27/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea


BOTTOM FIBER STRESSES

7/27/2019 Pres 230

28/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea


DEFLECTION

7/27/2019 Pres 230

29/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

Design Criteria exist in most Codes:

British Standards (BS8110 Part 1) ACI 318 (Chapter 18)

ACI 423 for un-bonded tendons

CAN3A23.3

Euro Codes

Concrete Society Technical Report 43

Design Checks

7/27/2019 Pres 230

30/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

Un-Factored Loads

Check Stresses

Maximum Tension

Maximum Compression Check Deflections

Serviceability Limit StateServiceability Limit State

Design Checks

7/27/2019 Pres 230

31/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

Allowable Stresses Design Classes

Class 1 - No Tension Allowed

Class 2 - Limited Tension (No Cracks) Class 3 - More Tension allowed

(Crack Width 0.1 to 0.2 mm)

Check at Critical Sections

Serviceability Limit State (Contd)

Design Checks

7/27/2019 Pres 230

32/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

Bending

SECTION FORCE RESULTANTS

Ultimate Limit StateUltimate Limit State

Design Checks

7/27/2019 Pres 230

33/43

EUROCODES


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

Non regular geometry easy to handle

EUROCODES

7/27/2019 Pres 230

34/43


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

7/27/2019 Pres 230

35/43

7/27/2019 Pres 230

36/43

EUROCODES

7/27/2019 Pres 230

37/43


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

PROBLEM..?!?.......

How to get all the

potential benefits offlat frameless PT

slabs,

AND

still provide suitable

resistance to lateral

actions?

Typical slab/column joint in PT slabs frameless slabs

EUROCODES

7/27/2019 Pres 230

38/43


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the FutureSlab to act as diaphragm

transferring lateral actions to shear walls

EUROCODES

7/27/2019 Pres 230

39/43


B

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the FutureFrameless PT slabs acting as

diaphragm only, for lateral loads resistance

7/27/2019 Pres 230

40/43

EUROCODES

7/27/2019 Pres 230

41/43

Workshop - 27-29 November 2006, Varese, ItalyB

uildingtheFu

tureintheEu

ro-Mediterran

eanArea

Building the Future

AlthoughEuro codesaddress pre-stressed concretestructures in general and flat slabs in another separate

chapter,

YET

Post-Tensioned flat slabs are not specifically covered andvery little is said concerning their detailing and mostly their

behavior with respect to seismic actions.

Lack of coverage

EUROCODESBuilding the Future

7/27/2019 Pres 230

42/43

Workshop - 27-29 November 2006, Varese, ItalyB

uildingtheFutureintheEu

ro-Mediterran

eanArea

A need to address

The increasing popularity of the use of Post-

Tensioned slabs in buildings should be enough

reason for properly regulating their design in theEuro codesup to the level of other national

current codes as in the ACI where a specific

chapter is dedicated for this technique.

7/27/2019 Pres 230

43/43

Documents

Pres 230