achieving simplicity for continuous teeroff bridges

Achieving Simplicity for Continuous Teeroff BridgesMichael Kakulas and Nick Keage

Reid/Tonkin Interchange

Project Overview

2

• Tonkin Hwy

− Reid/Tonkin Interchange to Maralla Road – 16km

• Reid Hwy

− Malaga Drive to Altone Road – 4km

• D&C Contract

• GNC

− BGC

− Laing O’Rourke

• AAJV – Joint Venture

− AECOM

− Arcadis

3 Northlink WA Central Section

Project Overview

• 25 bridge structures

• 15 Road bridges

− 5 continuous (up to 42m spans)

− 10 simply supported (21m to 38m spans)

• 1 Fauna bridge

• 3 Footbridges

• 6 Underpasses

• Nearly 12km of Noise and Screen Walls

• 8 Overhead gantries, 4 cantilever gantries

• Retaining walls


Project Overview, cont.

Design Development

5

• Five of the bridges were highly skewed bridges:

− Difficult to construct pier diaphragms

− Complicated to design and difficult to construct link slabs

• Continuous design need to avoid:


Why Continuous?

− Transverse diaphragms

− Additional formwork


Development

HEADSTOCK

COLUMN

ORDINARY REINFORCEMENT

DECK PRECAST BEAM

INSITU DIAPHRAGM

STRANDSEND BLOCK

TEMPORARY SUPPORTS

Transverse in-situ diaphragm

COLUMN

DECK

STRANDS

VOID


Development, cont.

SOLID END BLOCK

PRECAST BEAM

DECK

STITCH

STRANDS


Development, cont.


SOLID END BLOCK

PRECAST BEAM

COLUMN

VOID

DECK PRECAST BEAM

STITCH

STRANDS


Development, cont.


SOLID END BLOCK

LIFTING LOOP

COLUMN

VOID

DECK PRECAST BEAM

STITCH

STRANDS


Development, cont.


SOLID END BLOCK

LIFTING LOOP

TEMPORARY SUPPORTS

COLUMN

VOID


Tender Stage Details


Tender Stage Details, cont.

• No requirement for any on site formwork

• No requirements for post tensioning

• No grouting of the stitch joint required

• No additional reinforcement in the Teeroff


Improvements over other methods

• Shear transfer

− Bars protruding from web

− Cast-in plates

− Couplers

− Shear key

− Corbel


Change from Tender Design

• Shear transfer


− Cast-in plates

− Couplers

− Shear key

− Corbel




Adopted Stitch Design

Detailed Design

21

Design – Strut & Tie

• ‘Indirect support’

• Strut and tie design

• Shear key monolithic with teeroff beam

• Reinforcement placed according to

strut and tie model

• Interface shear capacity across critical

shear planes


Shear in webs ‘hung up’ by T2

ties

Shear transmitted from teeroff to stitch through

shear key

Transverse tension carried by T1 deck

reinforcement

Shear plane through corbel

and deck

Shear plane between teeroff

and deck

Shear transmitted to bearing through

C1 & C2 struts

Bearing reaction

Insufficient shear capacity

across this interface

Design – Unstressed Strand Anchorage


• Development Length

• 150db = 2280mm (without onion anchor)

• 106db = 1610mm (with onion anchor)

• Onion anchor contributes additional

bond and mechanical resistance

• Bond resistance from the increased

surface area of the individual wires

• Mechanical resistance from the ‘virtual

work’ of the individual wires

• Onion anchor easily formed by precaster

Design – Anchorage of Positive Moment Reinforcement


During Construction

• Clause 8.1.8.3(a) AS5100.5

• Fully tensioned strands and passive

reinforcement in teeroff web

In-Service

• Clause 8.1.8.3(c) AS5100.5

• Untensioned strands protruding from teeroff and

passive reinforcement in stitch

Strands projecting from end block

Ordinary reinforcement

Temporary prop

Anchorage reinforcement

In-situ Stitch

Design – Hog Capacity


Precast End Block

Design – Durability


• Stitch insulated to minimise risk of

thermal cracking

• Early age plastic settlement cracking

managed by recompacting the concrete

as cracks are observed

• Crack control reinforcement provided in

each direction

• Concrete over the stitch covered by a

waterproof membrane

• No cracking observed

Design – Reinforcement Detailing


Construction Sequence

1. Construct substructure

2. Erect temporary props

3. Install teeroff beams

4. Place deck and stitch reinforcement

5. Cast deck and stitch

6. Remove temporary props

7. Complete all other construction

activities



• Staged deck pours for larger bridges


Pour 1Pour 2 Pour 4 Pour 3 Pour 5

Span 3Span 2Span 1



Bearing plate

Bearing plate

Bearing

Teeroff

Galvanised formwork

Blockout in bottom flange

Strands projecting from end block

ELEVATION

PLAN



Stitch void



First stage deck pour



Curved and highly skewed bridge

Benefits of Proposed Detail

• Reduced:

• Structural depth

• Material quantities

• Transfer strength

• Construction cost

• Eliminated:

• Link slabs

• Transverse pier diaphragms

• Tapered bearing plates

• Didn’t Require:

• Additional formwork

• Post-tensioning

• Specialised construction techniques


achieving simplicity for continuous teeroff bridges

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