CommBank Stadium Description
CommBank Stadium (formerly Bankwest Stadium) is a 30,000-seat stadium in Parramatta, NSW Australia. The large 28,500m2 regional stadium is an initiative backed by the NSW Government to create an entertainment venue that was “made for the fans”.
Fabritecture’s scope was the design & construction of the impressive lightweight fabric structure roof utilizing a combination of Chukoh FGT-800 PTFE to provide shade to patrons and 300µm clear ETFE film eyelid roof to support pitch growth by allowing UV and natural light to pass through the membrane.
A large focus of the grandstand design was to bring patrons as close as possible to the field, creating a truly spectacular experience for all sports fans.
DESIGN / FABRICATION / INSTALLATION BRIEF
The CommBank Stadium in Parramatta, formerly known as Bankwest Stadium, delivers the ultimate in a live sports experience with the design of its seating bowl and roof taking intensity and atmosphere to a new level. The 30,000-seat rectangular stadium brings fans closer to their teams.
The stadium roof uniquely comprises of a combination of clear, single skin ETFE on the inner roof rim and PTFE/Fiberglass over the main part of the grandstand roofing. The PTFE provides shade and UV block to spectators below, while the ring of ETFE was incorporated into the internal edge of the roof to extend the drip line and provide full coverage without impacting pitch growth.
The PTFE panels are underslung on the steel work like a soffit, which allowed the use of simpler and less costly steel members. An unexpected side effect of the underslung fabric is the lovely shade lines of the steelwork through the membrane which change throughout the day as the sun shifts over the roof.
Another key feature is the night-time lighting effect onto the roof. LED lights shine onto roofing from inside stadium, and because the PTFE is underslung on the steel, the steel is not impacting the look of the roof – which appears fully covered without obstructions.
STRUCTURAL SYSTEMS
The primary objective of the project was for the main roof to appeal as a soffit-style roof where the main PTFE fabric is underslung off the steelwork to give clean lines from below while simultaneously hiding the supporting steelwork. A key benefit to the client of underslung fabric was the steel roof structure being hidden from spectators, allowing more cost-effective steel detailing as there was less focus on aesthetics.
There are 56 panels of PTFE fabric incorporated into the design, standardized to 10 different types. Typical size of the PTFE panels were 10m x 40m up to 15.5m x 40m. Standardizing the panels to as few different types as possible helped reduce fabrication and installation costs. Standard connection for the PTFE was under steel instead of on top.
The PTFE was tensioned not onto the main trusses but at an introduced member in the middle of each bay which was the ridge that the fabric was tensioned up to. The fabric low point is the underside of the main trusses, producing clean lines to make the whole roof look like a soffit. The fabric was connected mid bay span, allowing the fabric to wrap below the lower truss chord. This resulted in each fabric bay acting essentially as a large box gutter.
Barrier flaps are used in the roof’s design to stop debris from getting stuck (similar to a gutter guard) while still allowing water to move off the fabric and drain effectively into stainless steel sumps. By having the fabric bays join into a modified lower flange of a UC, a sheet metal flashing was used to cap the beam and overhang the fabric connection to create the weatherproof seal.
The clear single skin ETFE inner rim extended the drip line of the roof without impacting the pitch growth. An added advantage of the ETFE section of the canopy is that due to its natural ductility, it has a spoiler type effect – like an airplane wing but upside down – the spoiler generates down force on the canopy to prevent uplift. This helped reduce the overall steel weight also.
MATERIALS
For the roofing at CommBank Stadium, PTFE coated glass cloth was selected to provide shade and UV block to spectators below. Clear ETFE was incorporated into the internal edge of the roof to extend the drip line to provide full coverage without impacting the pitch growth.
The PTFE/Fiberglass is FGT-800 by Chukoh – selected for its high tensile strength, high durability (with design life of 35+ years), low maintenance (low friction coefficient of the Teflon coating means that it cleans with the action of rain), and non-combustible fiberglass substrate. It also has 14% light transmission providing a lovely daytime translucency, featuring the steel shadow lines through the roof and night-time LED backlighting.
The ETFE around the leading edge of the roof was specifically selected to allow UV light to pass through the membrane and assist in the growth of the pitch below whilst offering full cover rain coverage. 300µm clear ETFE by AGC was selected for the inner rim. The clear unfritted ETFE with 91% VLT provides maximum UV transmission to support growth of the pitch when under shade by the roof.
ETFE was considered as part of the overall LEED certification for the project due to its low carbon footprint. ETFE is 100% recyclable. At the end of its life it can be melted down and re-extruded for use in future installations. Due to its light weight, it requires minimal energy for transportation and installation. ETFE makes a significant contribution to ‘green construction’ of the stadium.
27,939m2 (PTFE/Fiberglass: 23,398m2; ETFE: 4,541m2)
FABRICATION
The corner panels of the roof were challenging as the panel width drastically changes from outer roof to inner roof, creating a wedge-shaped panel that is very difficult to deploy and tension. However, thoughtful design simplified 56 fabric bays into 10 standardized sizes.
Typical size of the PTFE panels was 10m x 40m up to 15.5m x 40 m. Standardizing the panels to as few different types as possible helps reduce fabrication and installation costs.
The ETFE component of the roof was comprised of clear single skin ETFE 300µm. There are 48 bays of ETFE covering 4,200m2 in total. Panel sizes were up to 150m2 per bay, with 8 bay variations – standard, corner, transition. The single skin ETFE is cable supported at 760mm centres.
COLLABORATION, CONSTRUCTION AND MAINTENANCE
The biggest and most complex feature of project construction was installing the PTFE fabric underneath the steelwork, as well as the methodology that we came up with as the solution. There were several factors to consider, including the safety of working at heights, and the hanging fabric before and during installation underneath the steelwork.
We devised an innovative solution for the underslung fabric installation, using cradle lifts by using 4 x chain motors and a swing stage style cradle that housed the PTFE fabric bundle. We lifted each PTFE panel from the pitch up to the underside of the roof creating a repetitive and productive deployment method.
The key to our successful installation of the roof structure was the flexibility that was incorporated into the installation methodology. This allowed for changes in other trades also working on site. When gantry was needed for lighting and sound installation, we stopped installing in one area and started in another. This was possible as one panel install was not dependent on the one before. Panels could be installed uniquely depending on the availability and accessibility at the time. The base extrusion was installed in the ground. Once deployed, we could move to the next panel. The methodology allowed for an average of one day to prep, one day to deploy and 3 days to tension. This averaged out to the installation of about one panel per day.
The lift for the ETFE installation was supported by a series of cables through cable pockets in the membrane.
COSTS
The CommBank Stadium PTFE & ETFE fabric roof was valued at AUD$7.4m.
Aerial shots of CommBank Stadium (photo credit: Ethan Rohloff)
PROJECT CREDITS
Project Name: CommBank Stadium
GPS Location: -33.808213192051454, 150.999730532382
Completion Date: 1-Apr-2019
Preferred Category: 4 – large structures >1,000m2
Entrant Name: Fabritecture
Address (Street): Unit 14/15 John Duncan Court, Varsity Lakes, QLD 4227
Telephone: +61 7 5587 7000
Mobile: +61 408 402 716
Email Address:
Website Address: www.fabritecture.com
Entrant Type / Role: Designer / Installer
Project Client: Lend Lease
Project Architect: Populous
Structural Engineer: Wade Design Engineers
Building Contractor: NSW Government
Fabricator(s): Confidential
