Case Study

The Olympic Cauldron

• Stainless steel gas burning structure
• 3D static, dynamic & buckling analysis
• Calculation of structural displacements for critical service connections

Tierney & Partners, one of the leading Australian Civil & Structural Engineering Consultancies are responsible for the structural design of the Olympic Cauldron, mast and transport components seen at the opening ceremony of the Sydney 2000 Olympic Games. LUSAS Civil & Structural analysis was used to assist with the development of this prestigious project.

The 8.5 tonne cauldron is a perforated, corrugated shell structure fabricated from stainless steel.  It has an overall diameter of 10m and tapers from 0.85m thick at centre down to 0.15m thick at the edge. During the opening ceremony it is raised from its submerged resting place beneath ground level and travels up an inclined cradle lift to a point from where it is then lifted up to a final position on a mast 50m above the ground. The cauldron was modelled in LUSAS Civil & Structural using 3D shell elements and 3D static, dynamic and buckling analysis was carried out to investigate self weight, wind, and dynamic effects caused during the transporting the cauldron to its final resting place.

The complex structure required an accurate stiffness assessment to be made. This was critical as the mechanical components needed to compensate for deflections at various stages of transport. LUSAS showed how the cauldron structure would perform under various transient loading and supporting conditions, and highlighted a number of elements with relatively high local stresses. If some elements or connections were to fail it was possible to foresee the re-arrangement of the load path and overall behaviour. This further increased confidence in the LUSAS model and hence the structure as a whole.

The LUSAS results confirmed preliminary assumptions that the stiffness of the shell, although corrugated, plays a major role in the strength and stiffness of the cauldron structure. Relying on the contribution of the corrugated and perforated shell, discretely connected to the internal frame, enabled this frame to be extremely light. Apart from an obvious cost effect, this proved to be critical as the project was nearing its completion and the weight of equipment was gradually increased from an initial 5 tonnes to a final 8.5 tonnes.

Results obtained were in the expected range. In fact, first results showed deflections slightly below initial estimates. However, this "benefit" was soon lost as more and more gas, electrical and mechanical equipment was added, increasing the original weight of cauldron by over 60% at the end of project. Due to presence of the shell the cauldron structure was able to absorb this increase in load without adversely affecting its performance. Furthermore, some connections, and in particular those critical ones near the cradle support for the cantilevering condition, had to be significantly modified to accommodate operational requirements (attaching and detaching gas lines and engaging/disengaging mechanical parts). Time did not allow re-modelling of the cauldron to test it against proposed changes. However, as a thorough understanding of the behaviour of the cauldron components had already been gained, it sufficed to alter some properties of the relevant components of the model, which enabled quick and practical modifications to be approved within hours of the request for change.

As Zlatko Gashi, engineer on the project says: 'when reliable and accurate understanding of the behaviour of the structure is required, it can only be achieved by taking into account all relevant structural components. Neglecting some components could grossly underestimate the strength and stiffness of the structure. Complex, sophisticated structures require a modelling and analysis tool such as LUSAS which can handle all the aspects of structural design, without burdening the designer with a further complexity of tool itself.  In addition, careful planning before the modelling, and envisaging potential future modifications and critical issues, is a key to successful design, and ensures that all benefits can be obtained from the model throughout the design and construction stage of the project."

Client stated benefits in using LUSAS on this project :

• Having such a sophisticated tool was essential. It would not be possible to model such a structure with less sophisticated tool.
• Easy, intuitive modeller.
• Plenty of element types which work together seamlessly.
• Easy staged modelling, with refinement of model as design progressed.
• Separate geometry layer and structure (attributes) layer. Once geometry is created, it is easy to experiment with various structural attributes.
• Ability to vary support conditions through load cases (no need to have separate models).

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