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Entered in the LSAA 2016 Design Awards (Cat 4 Large Fabric Structures, 4771)

Entrant: MakMax Australia (Engineer, Fabricator, Installer)

Location: Sleeman Sports Complex, Brisbane.   Completed: August 2016  Client: Watpac
Team: Cox Rayner Architects, Tensys, Arup, MakMax Australia

Application: Cycling Velodrome / indoor stadium

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Description

Large Clear spanning indoor stadium / velodrome to act as the Queensland State Centre and have capability for international events.

Design Brief

A significant driver for the project is the provision of a architecturally designed fabric structure facility, able to accommodate  the staging of the Gold Coast 2018 Commonwealth Games Cycling events.

Our scope was to design, engineer, fabricate and install the fabric component of this project

Structural Systems

The velodrome roof is saddle shaped form, slightly oval in plan and draining to the two low ends. The roof was originally conceived as a metal deck roof supported on 20 radial trusses spanning from guyed perimeter columns to suspend a central “oculus”. Both architect and builder were keen to explore the use of a fabric alternative.  The architect was interested in the freedom of form and natural daylighting possibilities.  The builder had concerns with the complexity of fitting purlins and sheet metal to a truss layout and geometry that did not suit the surface falls. Fabric also offered program advantages.

MakMax tendered a fabric alternative in 2 grades of fabric specifically chosen to optimize daylighting of the track whilst minimizing solar heat gain. These two grades of CHUKOH FGT-800 fabric were developed and made to order for this project.

Wind tunnel testing on the final form resulted in increased wind loads over the initial code studies, resulting in specific treatments on the edge extrusion to steel connections. Ponding concerns on the low slope roof were addressed by attention to detail – a relatively high pre-stress, use of top entry extrusion to help prevent initiation, setting the membrane level appropriately above steel bracing members and judicious variations to the slope of the roof at flat spots.

In total the project required the installation of 23 roof panels and 20 wall panels.

Materials

The large steel superstructure is clad on the walls and roof with a combination of opaque and translucent Tensioned Membrane Fabric, each offering different light transmission levels

Developed in conjunction with the fabric manufacturer two custom membranes were used

FGT 800-Blockout and FGT 800 - LT-8 which offers 8% translucency (compared to the standard 12%) and was installed over the track (oculus area ) to enable delivery of natural lighting to the track for cyclists and events.

Fabrication

All of the walls and half of the roof panels were produced in our state of the art fabrication facility in Japan. The other half of the roof panels were made in our production facility here in Brisbane. The PTFE membrane was cut to size on our custom built 20m membrane plotting table. The membrane panels were then fused together to form the shape of the roof using PTFE welding equipment. Membrane fabrication requires a high level of precision to ensure that the final product achieves its design parameters of shape and tension.

As the design relies upon regular fixing to the steel superstructure, it was necessary to develop a cost effective method for mid span fixing without any membrane penetrations.  Therefore both the roof and walls use a tee section detail that can be readily prepared in the factory and installed cost effectively.  Perimeter fixings had limited site adjustment, requiring significant analysis of the compensation data to achieve final design prestress.

Collaboration, Construction and Maintenance

Construction requirements were considered right from the design stage with consultation between the project management, design and construction teams. The installation method was developed to allow for weather, access limitations and OH&S requirements. Design meetings were held weekly with Watpac, Cox Rayner and ARUP to develop the membrane connections as well as the interface details with the perimeter steel claddings.

Design collaboration was undertaken using a controlling architectural geometry developed by Cox, which provided the centerline geometry for Arups and the steel detailers for fabrication.  As an overall design change was made, the centerline model would be fed into the shop detailers software to update the fabrication drawings as well as provide the new geometry for the engineers.  The weekly meetings allowed all parties to discuss the finer details and adjusted geometry as well as identify critical design items that affected the construction schedule (as the project was fast tracked some design items were still being resolved as their construction elements were taking place.

Long term, the PTFE membrane requires little ongoing maintenance with regular cleaning commensurate with any regular roofing material in order to maintain its appearance.