PROJECT APPLICATION AND DESCRIPTION: Zoological Enclosure
Structural Dynamics was contracted by The Slatter Group WA to assist with the design, material selection/supply and installation of a lightweight zoological enclosure that would cover an area of 90 meters long, 34 meters wide and 10 meters high.
The enclosure was covering two existing exhibits at the Perth Zoo, namely the penguin display and wetlands area, so needed to have minimal impact on the existing flora and infrastructure.
Pritchard Francis had already conducted the majority of the structural design and calculations of loads - Structural Dynamics assisted both The Slatter Group WA and Pritchard Francis with final material specifications to meet demanding requirements.
With such a large open enclosure that needed to be visually appealing for visitors as well as transparent for the exhibits inhabitants the challenge was to specify materials that met demanding load specifications but at the same time provided a light weight alternative that had minimal visual impact on the surrounding exhibits.
By suggesting a combination of stainless steel backstays, internal support cables and a fine stainless steel mesh the resulting enclosure has provided a light weight structure that was far superior from that originally specified by the client at no additional cost.
Structural Dynamics experience with structural cables, stainless steel materials and tensile architectural design has helped provide the client a structure that has already survived a 1 in 100 year storm in Perth, similar to the one that destroyed the original structure, and will provide a home for the exhibits inhabitants for many more years to come.
DESIGN / FABRICATION / INSTALLATION BRIEF
Structural Dynamics was contracted by The Slatter Group WA to provide expert advice on the provision of a zoological enclosure at Perth Zoo that was 100 meters long, 34 meters wide and 10 meters high.
Initial design work had already been undertaken by Pritchard Francis – it was the role of both The Slatter Group WA and Structural Dynamics to work together with the Perth Zoo to implement this structural design by recommending materials that would result in a functional and aesthetically pleasing light weight zoological enclosure that would maintain its form over time under high loads.
After numerous meetings with the client and design team Structural Dynamics recommended numerous changes to the concept design that resulted in less material but a stronger and longer lasting structure.
Some major recommended changes were:
Replacing 24mm galvanized backstays with 16mm/19mm stainless steel backstays;
Decreasing the amount of stainless steel cables used in the manufacture of the zoological mesh panels by sewing three panels together using Gore Tenara thread widely used in the specialized textiles industry;
Changing the layout of installation of the mesh panels to minimize wastage and unnecessary joins and seams in the structure.
After the final design was signed off by the client we worked closely with The Slatter Group WA to ensure the cable net structure was completed on time and on budget. This involved working other trades and the client to minimize the impact of the works.
4,800m2 of ClearMesh zoological mesh – this material was specified by Perth Zoo
100m of 19mm HAMMA Pro Strand 1x25 AISI316 stainless steel strand
100m of 16mm HAMMA Pro Strand 1x25 AISI316 stainless steel strand
38 units of 16/19mm P2H Adjusters compact architectural adjusters
Structural Support Cables
400m of 10mm HAMMA Pro Strand 1x19 AISI316 stainless steel strand
400m of 8mm HAMMA Pro Strand 1x19 AISI316 stainless steel strand
52 units of 8mm/10mm AM Adjusters architectural turnbuckles
Zoological Mesh Support Cables
6,000m of HAMMA X 7x19 AISI316 stainless steel wire rope
6,000m of 1.6mm Seizing Wire
The HAMMA Pro Strand was selected due to its high breaking strain properties and minimal stretch characteristics – as they key material used to hold the entire structure in place it was important to choose only the best materials available in stainless steel tensile architecture globally. The minimal stretch characteristic of this element was important, as the client was concerned with sag of the structure over an extended period. By selecting a compacted wire strand this minimized the possibility of this occurring and the designed light weight structure keeping its form.
The wire strand was partnered with key Strudyna stainless steel architectural fittings that both exhibited different key performance elements:
P2H Adjusters – with a unique internal thread system that enables adjustment without the cable turning this architectural fork allowed adjustment of the back stay cables under intense loads (up to 60kN). This assisted with the initial efficient installation of the structure as well as allowing subsequent fine tuning of the backstays and longer term adjustment if required;
AM Adjusters – the turnbuckle allows for bigger adjustment in the cables – as the longest cable was close to 90 meters in the structure – having a fitting that allowed for this to be put into tension confidently was important. The overall design and form of this structure would only be created if the cables were installed and tensioned correctly – the AM Adjusters used enabled this process.
Fabrication of the mesh panels was conducted by Pattons – a specialist in custom made shade sails and awnings based on Structural Dynamics specifications for the projects.
As some of these panels ended up being 6 meters wide and 34 meters long a specialist sail maker was employed to manage this process.
Due to the unique form of the structure each panel was lightly different and needed to be manufactured to ensure when in tension the overall design was not compromised.
Fabrication of the cable backstays and support cables was done onsite after the support columns were installed. The longest cable was close to 90 meters in length, which provided challenges in terms of tolerances and installation.
The main challenge in calculating the length of the cables was to take into consideration the loads that would be applied to the structure when in tension and ensure we met the key sag criteria of the zoological mesh panels from the client.
With a structure this size getting the supporting cable structure right was crucial in supplying a finished product that exceeded the clients requirements.
COLLABORATION, CONSTRUCTION AND MAINTENANCE
Installation of the components for this structure was made more difficult due to the limited access available on this site as the design intent which was to maintain as many of the existing established trees as possible – this was so when the works were complete the exhibit could be up and running again with the reintroduction of the fauna.
Structural Dynamics used a team of experienced riggers that was able to install the cable support structure to perfection, lay the netting and close the seams on time and budget – this was no small task considering the client wanted the seams closed at every join by using seizing wire at 50mm intervals – this resulted in close to 50,000 individual hand seizes being undertaken to ensure the structure would meet design specification.
Due to the design of the structure using stainless steel materials there should be minimal maintenance required.
Entrant: Structural Dynamics Australia
Category: 4 ID Number: 4966
Location: Perth Zoo, WA
Client: Government of WA - Department of Finance
Completion Date: January 2012
Architect: Pritchard Francis
Structural Engineer: Pritchard Francis
Builder: The Slatter Group, WA