Collaboration and Innoviation in Post-tensioned Waffle Slab

Col olla labo bora rati tion on and and Inn Innov ova ati tion on in a Po s t -Ten s i o n ed Waf f l e Sl Sl ab . Neeta City Shopp hopping ing Centre

Shaun Sullivan

Structural Systems (Northern) Pty Ltd

Introduction Collaborative Effort between Contractor, Consultant & Specialist Contractor

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


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


External Upstand Remained

Kerbs & Planter Upstand Removed


Existing Risers

Stormwater pipes through slab


Conforming RC Scheme • New waffle slab composite with existing PT floor Dowels @ 250cts & scabbling existing concrete

Reinf. Mat typ + extra bars at columns

Locate existing tendons Styrene void formers Ribs @ 1600max cts

Existing Tendons

PLAN Structural Systems (Northern) Pty Ltd

Construction Noise • Approx 30,000 Dowels & 8000m of 200wide scabbling • Scabbling and drilling outside business hours. Costly and timely! Night

Local Residents

Day

Woolworths Trading Hours

• Limited time to perform noisy work!


Night

Local Residents

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.


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





Core Connections • Bars epoxied into core • Sleeved for movement • 10mm isolation to existing slab


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

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


Column Connections • Column Reinf. Located • Oversized holes cores • Tapered isolation gap (preformed metal mesh) • Grouted at 56 days


Column Connections


‘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

Carpark

New Slab Existing Slab Woolworths


‘Back of House’ Hanging Load


Hanging Support • Very long span in 10Kpa area • Unable to span with available depth • Room underneath slab not available • Blade column introduced


Curved Beam • Irregular column grid • Extra concrete and DL required to span • Composite section used similar to RC scheme


Summary • PT solution eliminated significant amount of construction noise. • Minimal disturbances to existing tenancies • Savings in construction time. • Challenges solved through collaboration of interested parties Thankyou


Collaboration and Innoviation in Post-tensioned Waffle Slab

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