POST-TENSIONED SLABS IN BUILDINGS

EUROCODES

Workshop - 27-29 November 2006, Varese, Italy

Building the Future

Increasing popularity /versus/

Lack of specific coverage by Euro codesby

Guy A. TABETLEBANON

EUROCODES

Building the Future

Post-tensioned Slabs in Buildings

EUROCODES

Building the Future

PRINCIPLE

OF POST-TENSIONED

CONCRETE

EUROCODES

Building the Future

Illustrative example

2 P cosα

For harped profile

Three-span post-tensioned beam

Tendon

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

w =For parabolic shapeL2

8P x sag

EUROCODES

Building the Future

Free-body diagram of tendon

Free-body diagram of beam after removal of tendon

Force system between tendon and beam

Va W Vd

Illustrative example

EUROCODES

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

EUROCODES

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

EUROCODES

Building the Future

IN SLABStwo categories of PT systems are used :

Un-bonded system&

Bonded system

EUROCODES

Building the Future

• Single strand coated with corrosion inhibiting grease and encased in polyethylene sheathing

• PT force is transferred to the concrete by the anchors provided at the ends

Un-bonded Tendons

EUROCODES

Building the Future

EUROCODES

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 ductBonded system tendon detail

for beams & slabs

Strand position in a circular duct

Bonded Tendons

EUROCODES

Building the Future

EUROCODES

Building the Future

Structural Forms

EUROCODES

Building the Future

Structural Forms

EUROCODES

Building the Future

• Preferred Option– Flat Slab

• Minimum Thickness• Flat Soffit

Structural Forms

EUROCODES

Building the Future

LOAD BALANCING

A comprehensive solution to Post-Tensioningby T.Y.Lin

Simple - General – Powerfulfor 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

EUROCODES

Building the Future

Load Balancing

Three-span post-tensioned beam

Tendon

Design Concept

EUROCODES

Building the Future

Modeling of two way slab system

Methods available :– Equivalent Frame Method– Finite Element Method– ……….

Analysis of the Structure

EUROCODES

Building the Future

• Finite Element Model– Models a whole Floor – Actual Tendon Locations

• Plane Frame Model– Models a single sub-frame

EUROCODES

Building the Future

Most common modeling of gravity loading and post-tensioning:

– Slab systems are modeled as rows of intersecting two dimensional 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

EUROCODES

Building the Future

Typical slab frame

EUROCODES

Building the Future

STRUCTURE PERSPECTIVE

Finite Element Model

EUROCODES

Building the Future

ELEMENT MESH PLAN

EUROCODES

Building the Future

BANDED TENDON LAYOUT

EUROCODES

Building the Future

DISTRIBUTED TENDON LAYOUT

EUROCODES

Building the Future

TOP FIBER STRESSES

EUROCODES

Building the Future

BOTTOM FIBER STRESSES

EUROCODES

Building the Future

DEFLECTION

EUROCODES

Building the Future

Design Criteria exist in most Codes:• British Standards (BS8110 Part 1)• ACI 318 (Chapter 18)• ACI 423 for un-bonded tendons• CAN3 – A23.3• Euro Codes• Concrete Society Technical Report 43

Design Checks

EUROCODES

Building the Future

• Un-Factored Loads• Check Stresses• Maximum Tension• Maximum Compression• Check Deflections

Serviceability Limit StateServiceability Limit State

Design Checks

EUROCODES

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 (Cont’d)

Design Checks

EUROCODES

Building the Future

Bending

SECTION FORCE RESULTANTS

Ultimate Limit StateUltimate Limit StateDesign Checks

EUROCODES

Building the Future

Non regular geometry easy to handle

EUROCODES

Building the Future

EUROCODES

Building the Future

EUROCODES

Building the Future

IDEAL SOLUTION

FOR TOWERS

EUROCODES

Building the Future

PROBLEM…..?!?.......

How to get all the potential benefits of flat frameless PT slabs,

AND still provide suitable resistance to lateral actions?

Typical slab/column joint in PT slabs frameless slabs

EUROCODES

Building the Future

Slab to act as diaphragm transferring lateral actions to shear walls

EUROCODES

Building the Future

Frameless PT slabs acting as diaphragm only, for lateral loads resistance

EUROCODES

Building the Future

Numerous walls for increased lateral resistance, if necessary

EUROCODES

Building the Future

Although Euro codes address pre-stressed concrete structures in general and flat slabs in another separate

chapter,

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

behavior with respect to seismic actions.

Lack of coverage

EUROCODES

Building the Future

A need to addressThe increasing popularity of the use of Post-Tensioned slabs in buildings should be enough reason for properly regulating their design in the Euro codes up to the level of other national current codes as in the ACI where a specific chapter is dedicated for this technique.

EUROCODES

Building the Future

THANK YOU FOR YOUR ATTENTION

POST-TENSIONED SLABS IN BUILDINGS

Documents

Design of Post Tensioned Slabs on Ground

POST-TENSIONED IN BUILDINGS - VSL

"Design of Post-Tensioned Slabs-on-Ground" 3rd Edition

CARES Model Specification for Post-tensioned Slabs

bbr.plbbr.pl/download.php?pdf=0205_BBR_Flat_ang.pdf · Editorial: Advantages of post- tensioned flat slabs BBR's experience With post-tensioning slabs dates back to the early seventies

TWO-WAY POST-TENSIONED SLABS WITH BONDED TENDONS

Addendum No. 2 to the 3rd Edition of the Design of Post-Tensioned Slabs- on-Ground 2.pdf · · 2011-11-073rd Edition of the Design of Post-Tensioned Slabs-on-Ground 8601 N. Black

Post-Tensioned Concrete in Buildings ACI SF Bondy

Post Tensioned Concrete Floors in Multi Storey Buildings

Eprints Cover Sheet In multi-level building design, a fundamental principle of structural engineers designing post-tensioned slabs is that as the slabs are post-tensioned, a certain

PREDICTION OF DEFORMATIONS IN POST- …...PREDICTION OF DEFORMATIONS IN POST-TENSIONED PRESTRESSED SUSPENDED SLABS IN TALL BUILDINGS Thomas J. Vincent B.E. Civil Engineering (Hons.)

NZ EXPAN Post-Tensioned Timber Buildings - June 2013 ...assets2.expan.co.nz/assets/NZ-EXPAN-Post-Tensioned...2013-presen… · 6/7/2013 1 Post-Tensioned Timber Buildings - Design

TWO-WAY POST-TENSIONED SLABS WITH BONDED TENDONS … Repr… · PTI JOURNAL TECHNICAL PAPER TWO-WAY POST-TENSIONED SLABS WITH BONDED TENDONS By Kenneth B. Bondy Authorized reprint

POST-TENSIONED SLABS - CCL Norway (LR...CCL Post-Tensioned Slabs are the first choice for many architects, contractors and engineers around the world. The intelligent use of post-tensioning

POST-TENSIONED SLABS · 2019-10-21 · efficient floor slab design creates longer spans and reduces the need for columns within the structure. ... CCL Post-Tensioned Slab systems

Post – Tensioned Concrete Slabs

Modelling of Unbonded Post-Tensioned Concrete Slabs Under ... · unbonded post-tensioned slabs. The slabs were designed accord-ing to BS 8110-1 [22] and the Concrete Society Technical

Flexural Behavior of Post-tensioned Lightweight Concrete ... · PDF fileFlexural Behavior of Post-tensioned Lightweight Concrete Continuous One-Way Slabs Keun-Hyeok Yang1), Yongjei

Real Fire Test on Concrete Columns and Post-tensioned Slabs · Real Fire Test on Concrete Columns and Post-tensioned Slabs . IAN BENNETTS and WARREN SOUTH* Centre for Sustainable

OF TWO-WAY SLABS AND PLATES - Imcyc en dos Direcciones... · DESIGN OF TWO-WAY SLABS AND PLATES 11.1 INTRODUCTION REVIEW OF METHODS Except for post-tensioned slabs, supported floor