LSAA 2011 Design Award Entry
APPLICATION OF PROJECT: Separation Enclosure for Chimpanzees.
The Taronga Zoos’ chimpanzee troop is one of the largest captive groups in the world with recognized wild behavior patterns and a sophisticated social hierarchy. With its population including four maturing sub-adult males jockeying and promoting themselves within the group, the zoo cited a need for the construction of a fully enclosed and semi-transparent separation paddock within the chimpanzee exhibit to allow the chimpanzees to be easily divided as needed, without moving them to an entirely new location, and thus avoiding potential commotion.
The Seperation Enclosure:
- facilitates the introduction of new chimpanzee females to maintain the genetic pool.
- provides the necessary infrastructure for the current troop management strategy and philosophies.
- permits the troop to remain outside in summer unsupervised where this was previously not possible.
- maximizes viewing time for the public.
The Taronga Zoo Separation Enclosure represents one component of the upgrade of the heritage listed Taronga Zoo Chimpanzee Exhibit built in 1980.
The “free form” fully enclosed “Aviary style” separation enclosure is of tensile cable net construction and utilizes Carl Stahl X-Tend stainless steel wire mesh as part of the primary load carrying structure to carry the loads in the membrane rather than via a heavy steel sub-structure. The structure itself encloses a useable paddock area of 470m2. It is comprised of three main components, each complex in its own right, with all three combining to ensure an enclosure of maximum safety, security and transparency:
- the free-form enclosure mesh and cable net.
- the masts with their integrated climbing structures and platforms (a world first).
- an independent inclined non-climb cable net wall on the S/E face of the enclosure to prevent Chimpanzees from climbing from the adjacent paddock over the outside of the Aviary enclosure.
DESIGN / FABRICATION / INSTALLATION BRIEF
In addition to the zoological requirements, detailed above, relevant factors influencing the final built form of the enclosure had to consider:
- Views from the harbor – the highest new built element:
- had to sit below or within the horizon escarpment vegetation zone.
- had to disappear behind foreground vegetation or existing buildings.
- Built form -
- the form and height of the structure had to provide a 3 dimensional space sufficient for chimp well being, climbing poles and platforms compliant with EAPA.
- the Aviary mesh structure’s form had to be irregular - not regular or “box-like” to blend in with the surrounding tree patterns.
- the structure had to be multi faceted resulting in levels and degrees of mesh transparency.
- the design had to minimize or eliminate horizontal and vertical forms.
- Building height – the highest point of the structure was to be no higher than 12m above the ground.
- Impacts on adjacent exhibits had to be considered.
- Materials –
- black coloured mesh with areas of non-climb perforated metal to match the mesh – both being semi transparent.
- Masts had to be clad in natural timber to approximately 450mm diameter to replicate a natural climbing experience.
- Landscape and character – The structure had to accommodate significant plantings of mature palms and trees and make use of the natural form and topography of the site.
- Consider the heritage status of Taronga Zoo as an item of state heritage significance.
Ronstan Tensile Architecture, Jackson Teece and principal contractor, Lipman Pty Ltd considered these unique challenges, resulting in the construction of a divisible “aviary-type” free-form tensile enclosure and open paddock. Lipman engaged Ronstan for the detailed design and installation of the enclosure, which included masts, cables, mesh and non-climb wall panels. In a collaborative effort, all three worked to ensure that the intent and function of the enclosure was reflected in the unique and complex final Ronstan design.
Working closely with design partner, Officium Design Engineering, Stuttgart, the design parameters of the mesh and integrated cable net were generated. Once the overall system geometry was confirmed through design consultation and the use of a scale model, finite element analysis of the system was performed to determine the required forces that all structure and foundations were to be designed to. Reaction loads to foundations/footings and other mating structures were determined so that all surrounding supporting structures could be properly designed to support the mesh enclosure and non-climb wall structure.
Through the enclosure design and non-linear analysis the final mesh form was established and Ronstan was able to introduce a number of key changes that improved the design and ensured tighter compliance with the brief:
- The masts were centralized to a common footing to better resolve the forces.
- A change was made from fixed mast bases to flexible to enable the structure to move and help reduce the size of the mast and loads to the footings.
- Mast sections were changed from cruciform section to RHS to improve their torsional performance and to reduce the mass of timber required to clad to a diameter of approx.450mm.
Non –Climb Wall
By far and away the largest design innovation involved the non-climb wall. As a “world first” a transparent cable-supported ‘non-climb wall’ was integrated into the structure to prevent chimpanzees from climbing up the walls of the enclosure from the adjacent outdoor paddock. This is unique and highly technical arrangement called for thorough and detailed analysis, co-ordination, planning and execution to ensure that the structure was buildable and could be delivered in a safe and cost efficient manner. Tensys Engineers were engaged to engineer the non-climb cable net wall and to certify both structures to Australian standards. The non-climb wall was constructed of 22mm 1x19 catenary cables with 8mm vertical dropper cables forming a net to which 192 panels of blackened 3mm perforated stainless steel sheet were clamped. Panels were overlapped to ensure the chimps could not get a finger hold and the whole structure inclined by 10 degrees to ensure it could not be climbed.
The non-climb wall (NCW) had been designed with wall panels clamped directly to the enclosure mesh face. It was changed to an independent cable-net structure:
- to remove the risk of having the final NCW shape differ from that modeled, and in so doing, to avoid the risk of panel geometry differing.
- to facilitate the 10 degree incline of the NCW necessary for “non-climbability”.
- to ensure uniform set out and fixing methods and to ensure more consistent panel shapes.
- to accurately match the architectural intent/geometry of the NCW and allow panel geometry to drive the NCW structure rather than this being determined by other elements.
Carl Stahl X-Tend mesh was selected for this project for its unique qualities of strength, resistance to corrosion and flexibility. The mesh is manufactured of 3mm stainless steel 7 x 7 wires connected at 60mm intervals (mesh aperture) with stainless steel ferrules to form a mesh. The mesh was blackened to ensure maximum transparency. It was imperative that the mesh used was strong enough to resist loads applied by the chimps yet forgiving enough so as not to injure the animals. Other meshes manufactured by opening individual strands of wire to “weave” a mesh are significantly weaker.
90 x 250 RHS clad to an approximate outside diameter of 450-500mm in old growth red iron bark timber.
Cables & Clamps
Ronstan G316 Stainless Steel 1x19 construction chosen for strength and performance.
Non-Climb Wall Panels
3mm T304 Stainless Steel panels perforated with 4.76 Dia holes to achieve 50.96% open area – the desired level of transparency.
Ronstan was fully responsible for the design and installation of the structure including masts, cables, mesh and non-climb panels. Installation of these elements called for careful planning and execution and required the use of a full birdcage scaffold inside the structure to enable installers to deal with the mesh’s unique and complex behaviour. At its highest point this represented a height of 7 floors above the ground.
A temporary 3mm cable net was constructed over the complete enclosure at the required geometry. With masts propped at the final positions permanent cables tying the masts together were placed in position, again at a pre-determined geometry. Mesh panels were then laced into position and tensioned into place to match the required geometry. In its final resting position the mesh represents one homogeneous membrane carrying the loads of the structure and lifting the masts off the props and into their pre-determined locations.
All joints, pins, screws, bolts and fasteners had to be tamper-proof with cable fittings and turnbuckles welded to ensure they could not be interfered with by the Chimpanzees.
COLLABORATION, CONSTRUCTION AND MAINTENANCE
Due to the complex nature of the geometry and the number of design stakeholders (Sydney, Melbourne, Stuttgart) Ronstan decided to model the complete structure to ensure we followed and achieved the geometric intent. It was determined that this would be too complex to achieve in a 2D environment.
The model was developed from the 3D line representing the bottom connection of the mesh, which had been provided by the architect. The 3D Model was used as the basis for all shop drawings of steel and panels and allowed the smooth development of other details/elements for other trades.
As an example the model was provided to the fabricator of the Non-Climb Wall steel panels. 192 individual panels were manufactured from the model with all installed on site to within a 5mm tolerance.
The model was adopted as the true and correct model for the project and was used by all partners.
Maintenance is provided in accordance with the warranty.
Project Number: 2019
Title: Taronga Zoo Chimpanzee Enclosure
Location: Mosman NSW
Entrant: Ronstan Tensile Architecture
Client: Taronga Conservation Society Australia
Architect: Jackson Teese Architecture
Structural Engineer: Hughes Trueman
Spec Consultant: Officium Design Engineering
Others: Tensys Engineers
Builder: Lipman Pty Ltd
Fabricator: Ronstan, Carl Stahl
Steelwork etc: All Steel