It is quite a challenge to create an enclosure with barriers designed to absorb the impact of an adult tiger colliding with a wall running at a speed of 40 kilometers per hour. The designers and engineers creating a permanent home for the Sumatran tigers at the Taronga Zoo, found the perfect solution using Carl Stahl X-Tend Tensile Mesh with flying masts and structural cable support. Ronstan served as the tensile architecture specialist design and construct subcontractor to ensure the structure would look and perform as intended.
The Sumatran Tiger Exhibit consists of three separate enclosures, all located on a complex and steep site on a rocky hill, with several large trees to incorporate into the design. The project team had a reasonable idea of how they wanted the enclosures to look and perform, so Ronstan had a good starting point for the wire mesh form for structural and detailed design. A full 3D model of the structures was done first, which included a site survey and the major trees and tree branches digitally scanned. The theoretical forms of the mesh enclosures and other structures were introduced into the 3D model and cables and steelwork were fabricated in accordance with the 3D models.
This project differed from previous zoological enclosures Ronstan has designed and built. This structure, in particular, the roof elements, required the mesh to be planned and installed at a higher pretension. Unlike tensile fabric, the tensile mesh weight is significant and so getting the install tension right is essential to achieving the required mesh surface geometry and position in 3D after installation.
Carl Stahl X-Tend Tensile Mesh was used in all three enclosures in unique ways. X-Tend is fabricated from stainless steel wire ropes joined together to form diamond shaped apertures with stainless steel ferrules. The aperture of the diamond is notionally regular with internal aperture angles of 60 and 120 degrees. The shape of the diamonds can, will and did vary across a free-form surface and the mesh tension varies as diamond shape changes. In order to better understand the biaxial stiffness of the tensile mesh, Ronstan undertook biaxial testing of mesh measuring its behavior at different pre-stress levels.
Two of the enclosures are free form tensile roof canopies constructed from wire mesh, effectively acting as a tensioned cable net structure. The mesh is tied to catenary cable boundaries connected to masts with tieback cables and is pushed and pulled up with 4 flying masts in each enclosure. The flying masts are supported on a structural cable net that is attached to a large central mast and tied back to the perimeter masts structures. On these two enclosures, there are also free-form tensioned X-Tend Tensile Mesh walls that are suspended from the X-Tend Mesh roof structure and tied to the ground or to other viewing and husbandry buildings projecting into the enclosures. These mesh walls provide a barrier strong enough to contain the tigers, with the best viewing experience for visitors.
The roof of Enclosure 3 (colloquially named “Enclosure Tree”) had an even higher degree of difficulty as it is interleaved through an ancient, heritage listed Moreton Bay Fig tree. Suspended within the roof is a series of pre-planned rings that frame the opening for large tree branches as they project through the X-Tend Tensile Mesh roof surface. Mesh strips were required to be manually spliced, and threaded around and through the fig tree as designed.
Enclosure 2 is a more conventional structure with tensioned X-Tend Mesh walls above lower concrete walls. The mesh is stretched over curved steel frames and has a cable border along its top and bottom edges.
In order to ensure the correct tension for the application, the wire mesh panels were pre-planned rather than rigorously patterned. The panels were made oversize but then marked out in the factory with our prediction of where the mesh was expected to cross the cable boundaries and attach to the flying mast rings and the tree ring openings. Mesh panels were fabricated in strips that could be manhandled and spliced together on site to form homogeneous complete surfaces.
Installation occurred in planned stages. The masts were installed propped at correct final positions (including the flying mast rings) and a temporary webbing net was then installed to hold the edge cables in position. The webbing net also provided support for the X-Tend Mesh as it was positioned and deployed ready for tensioning. The X-Tend Mesh strips were then manually spliced and threaded into place.
Once spliced the mesh was then tensioned with ratchets gradually lifting it into position, a process that involved working carefully to ensure that once the mesh sat at the correct levels on the site it was also at the correct tension. Once the mesh was correctly positioned it was adjusted and laced to the perimeter cables and internal rings on the flying masts. The successful installation required detailed collaboration with builders, contractors and subcontractors.
The final result of the Sumatran Tiger Enclosure at the Taronga Zoo is an immersive, stunning visual experience for visitors and a safe and perfect habitat for these endangered tigers.
Taronga commented on their website that it, “prides itself on being a leader in the presentation, conservation and research of wildlife. This important redevelopment work is part of the natural expansion of our efforts to help save the critically endangered Sumatran Tiger.”
All photos by Simon Dallinger Photography