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Collaboration and Innovation in a Post-Tensioned Waffle
Slab.
Neeta City Shopping Centre
Shaun Sullivan
Structural Systems (Northern) Pty Ltd
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Introduction
Collaborative Effort between Contractor, Consultant &
Specialist
Contractor
A Solution to your Weighty Problem A Post Tensioned Waffle
Slab
Structural Systems (Northern) Pty Ltd
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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
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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
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External UpstandRemained
Kerbs & Planter Upstand Removed
Structural Systems (Northern) Pty Ltd
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Existing Risers
Stormwater pipes through slab
Structural Systems (Northern) Pty Ltd
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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
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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
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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
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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
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Structural Systems (Northern) Pty Ltd
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Structural Systems (Northern) Pty Ltd
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Structural Systems (Northern) Pty Ltd
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Core Connections Bars epoxied into core
Sleeved for movement
10mm isolation to existing slab
Structural Systems (Northern) Pty Ltd
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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
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Column Connections Column Reinf. Located
Oversized holes cores
Tapered isolation gap (preformed metal mesh)
Grouted at 56 days
Structural Systems (Northern) Pty Ltd
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Column Connections
Structural Systems (Northern) Pty Ltd
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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
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Back of House Hanging Load
Structural Systems (Northern) Pty Ltd
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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
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Curved Beam Irregular column grid Extra concrete and DL
required to span Composite section used
similar to RC scheme
Structural Systems (Northern) Pty Ltd
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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
