Collaboration and Innovation in a Post-Tensioned Waffle Slab.

Neeta City Shopping Centre

Shaun Sullivan

Structural Systems (Northern) Pty Ltd

Introduction

Collaborative Effort between Contractor, Consultant & Specialist

Contractor

A Solution to your Weighty Problem …– A Post Tensioned Waffle Slab

Structural Systems (Northern) Pty Ltd

Project Overview• Extension and refurbishment of the Neeta City Shopping Center,

Fairfield

• Existing 1st Floor car-park converted to a new Big W Store.

• Approx 5800m2

• New Floor 300 to 400mm above the existing car-park floor.

• Floor Live Load increased from 3kPa to 5KPa / 10kPa

Structural Systems (Northern) Pty Ltd

Project Constraints• Operating Woolworths supermarket in floor below +

carpark over

• No space beneath could be used for construction

• No significant construction noise during business hours.

• Weight of new floor less than slab capacity.

• Relatively long spans & falls in carpark

Structural Systems (Northern) Pty Ltd

External UpstandRemained

Kerbs & Planter Upstand Removed

Structural Systems (Northern) Pty Ltd

Existing Risers

Stormwater pipes through slab

Structural Systems (Northern) Pty Ltd

Conforming RC Scheme• New waffle slab composite with existing PT floor

Locate existing tendons

Dowels @ 250cts & scabblingexisting concrete

Styrene void formers

Reinf. Mat typ + extra bars at columns

Ribs @ 1600max cts Existing Tendons

PLANStructural Systems (Northern) Pty Ltd

Construction Noise• Approx 30,000 Dowels & 8000m of 200wide scabbling

• Scabbling and drilling outside business hours. Costly and timely!

Day NightNight

Woolworths Trading Hours

LocalResidents

LocalResidents

• Limited time to perform noisy work!

Structural Systems (Northern) Pty Ltd

Alternative PT Scheme• Post-tensioned waffle slab

• Isolated from the existing floor surface.

• Connection to Existing Columns by Dowels

• Temporary IJ to existing columns to allow movement.

Structural Systems (Northern) Pty Ltd

Typical Scheme Details• 200 wide ribs @ 1500 cts• Joint locations reflect existing slab• 90mm thick RC slab between ribs• Pour strips for stressing access• Bond breaker to existing slab

Structural Systems (Northern) Pty Ltd

Structural Systems (Northern) Pty Ltd

Structural Systems (Northern) Pty Ltd

Structural Systems (Northern) Pty Ltd

Core Connections• Bars epoxied into core

• Sleeved for movement

• 10mm isolation to existing slab

Structural Systems (Northern) Pty Ltd

Why Isolate?• Typical Slab – Columns deflect to accommodate PT force

• As slab is poured directly on existing, columns cannot deflect - post-tensioned force ‘lost’

Structural Systems (Northern) Pty Ltd

Column Connections• Column Reinf. Located

• Oversized holes cores

• Tapered isolation gap (preformed metal mesh)

• Grouted at 56 days

Structural Systems (Northern) Pty Ltd

Column Connections

Structural Systems (Northern) Pty Ltd

‘Back of House’ Hanging Load • Wider ribs (extra DL) required

in 10KPa area

• Unable to prop from below

• Load hung from carpark slab over

• ‘Reidbar’ threaded reinforcement & plates

Woolworths

Carpark

New Slab

Existing Slab

Structural Systems (Northern) Pty Ltd

‘Back of House’ Hanging Load

Structural Systems (Northern) Pty Ltd

Hanging Support• Very long span in 10Kpa area• Unable to span with available

depth• Room underneath slab not

available• Blade column introduced

Structural Systems (Northern) Pty Ltd

Curved Beam• Irregular column grid• Extra concrete and DL

required to span• Composite section used

similar to RC scheme

Structural Systems (Northern) Pty Ltd

Summary

• Minimal disturbances to existing tenancies• Savings in construction time.• Challenges solved through collaboration of

interested parties

Thankyou

• PT solution eliminated significant amount of construction noise.

Structural Systems (Northern) Pty Ltd