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Inside the Millennium Dome

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Engineering the unique Millennium Dome has presented a number of engineering challenges, including predicting the internal environment. The team's concept is that, simply viewed, this is an 'umbrella' structure under which other buildings, exhibitions and facilities 'spawn'. To try to 'treat' (heat or cool) the whole volume of the Dome would have resulted in vast energy usage. The analogy must be that of a grand rail station. Visitors are dressed according to the external climate. Only when they enter the 'smaller' exhibitions will they encounter treated environments.

Under this umbrella, a network of utility services laid in the ground slab will provide pick-up points for power, water, chilling and communications. This allows for the 'spanned' structures to heat and cool their environment to suit. Nevertheless the thermal environment of the Dome is a factor in how the visitor will perceive the whole Dome experience. There are many fabric structures throughout the world, but scale and content make the Greenwich structure unique.

Our starting point in thermal modelling work was clearly stating the base input conditions upon which the model could be built. Firstly, tas 2D modelling defined boundary conditions such as surface temperatures. These data were then transferred to a three-dimensional cfx computational fluid-dynamics model. For this Buro Happold employed the service of aea Technology in Harwell. Firstly a 3D model was constructed. While this was informative at the time, it soon became clear that to get the full picture and the inter-reaction between the different exhibition structures, a full 360degrees model with an accurate picture of the internal geometry of all the internal building would be needed.

This model is currently being developed at aea. The likely size of the model will be 700,000 cells. It will take three to four days to run one scenario.

The Dome volume is not a conditioned space, but it does have significant energy effects. The major elements of these - apart from its boundary input, such as solar gain - are the gains from the 'exhibition' and the potential 35,000 visitors.

In order to ensure public safety, Buro Happold fedra used state-of-the- art fire-modelling techniques to analyse production of smoke from a fire and to calculate means of escape. Computational fluid-dynamics models were used to design smoke management systems. The model, probably the largest of its type, was run on a super-computer and included effects of wind and micro-climate. fedra used the Building exodus evacuation model to model the flow of people in a fire situation. The escape strategy accounts for both able and disabled people.

There is still an awful lot to do but fortunately we have a great team on the project, and morale is excellent.

Ian Liddell, Tony Mclaughlin, Mick Green, Glyn Trippick

Architect: Richard Rogers Partnership

Structural, building services, fire, geotechnical and civil engineer: Buro Happold

Stuttgart 21 Railway Station

The complex, underground railway station for Deutsche Bahn ag in the city of Stuttgart is an exciting, modern freeform structure, designed with modern methods of analysis, physical modelling and visualisation.

For centuries, builders and engineers have supported high loads on massive vaulted masonry and un-reinforced mass-concrete structures. Most are arranged with form-resisting permanent external loads through direct compression, allowing adjacent blocks to be joined by mortar.

Developing these ideas, the Stuttgart Station design uses reinforced concrete as a cost-effective sculptural material to form a naturally lit, enclosed public space. Twenty-nine nearly identical flowing shell forms transfer loads from gardens above into foundation systems below. This preserves the greatly valued Schlossgarten central park and allows the transformation of the existing 1922 terminal into a multi-line through station. Natural daylight is introduced into the underground space through glazed skylights tilted towards the sun. The 60m 30m primary column spacing meets the complex functional requirements of the new station as well as the formal relationships necessary to complement the listed Bonatzbau building that lies adjacent.

To create a continuous stable environment, the 3D-shell form has been manipulated to maximise areas of concrete in direct compression, minimising bending moments. This approach helps in technical consideration of effects of long-term creep, shrinkage and temperature differentials while optimising material thickness and quantities.

The fundamentals of this engineering process are demonstrated by the physical 'hanging' chain model constructed with Frei Otto for an area of vaulting immediately adjacent to one column support. Inverting the model shows the vaults resist dead-weight loads by the three-dimensional flow of axial compression. This structural analysis is used, with numerical models, to generate first forms for global analysis.

The use of continually refined and developed physical, virtual and mathematical models is a vital aspect of the design process. The project will require full definition of upper and lower shell surfaces, boundaries and associated volumes. Mathematical models and 3D solid forms are under development using computer software developed for shape definition in the automobile industry. These digital representations will be combined to form 3D finite- element models to be analysed for stress, force-flow and deflections. Stereo lithographic modelling and other rapid prototyping techniques routinely used for commercial product development will be used for effective visualisation and communication of the design.

The holistic approach embracing physical modelling and computer analysis allows us to maintain an objective view in development of the structural form.

Paul Westbury, Darrell Morcom, Michael Dickson, Klaus Leiblein, Michael Vitzhum

Architect and general planner: iokp

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