michael 2007-9-30 16:58
OASYS实例Melbourne Cricket Ground Redevelopment
[align=left][color=black][float=right][attach]1221[/attach][/float]Melbourne Cricket Ground (MCG) is one of the icons of Australian sport. Besides cricket, a highlight of which is the annual Boxing Day Ashes Test Match, it is used for Australian rules football during the winter, culminating in the Australian Football League (AFL) Grand Final in September.
In 1999, the Commonwealth Games Federation chose Melbourne to host the 2006 Commonwealth Games. However, a requirement was that the north side of MCG would undergo major redevelopment in order to bring it inline with a 21st century sporting venue with a 100,000 capacity. To achieve this, the client body, comprising the Melbourne Cricket Club (MCC) and the MCG Trust, brought together a group of five architectural practices under the title of MCG5 and appointed Connell Wagner and Arup to deliver the multidisciplinary engineering design.
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[color=black][b][float=left][attach]1222[/attach][/float]The Northern Stand Roof[/b][/color][/align]
[color=black]Design of the $425M MCG Northern Stand redevelopment began in 2001, with the new roof as the most striking visible feature of the stadium. With its iconic location, the final roof design needed to be a globally recognizable symbol for Australia's sporting citadel. The design aim was thus for it to be elegant, light, and transparent, but also distinctly Victorian and in harmony with the existing Great Southern Stand and existing light towers.
[float=right][attach]1223[/attach][/float]The engineers developed several options for the structure, each tested against architectural, cost, and staged construction requirements. The final innovative design incorporated a tension structure with rafters suspended from cable stays running over individual masts and back props. This created an ideal balance of unique geometry and construction practicality, which would be aesthetically complementary rather than dominating.
The engineers modelled the entire roof structure with GSA. This enabled accurate analysis of the various wind loads and made it possible to test the impact of design and geometry changes quickly and efficiently.
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[float=right][attach]1224[/attach][/float]
Cablenet[/b]
The key feature in making the roof structure efficient, architecturally elegant, and lightweight is the cablenet. Preliminary wind tunnel testing had shown that the uplift forces acting on the roof would occur in an alternating pattern of high peak regions and low troughs. Rather than design each bay to resist these peak loads individually, the team developed the supporting cablenet to distribute the load more widely and engage additional stiffness from adjacent bays. The use of counterweights to resist uplift also enabled the use of thinner cables, resulting in a visually superior design. Due to the distributing benefit of the cablenet, the design team was able to reduce the amount of counterweight 50%. Aside from distributing peak wind loads and reducing counterweight, the cablenet restrains the top of the individual masts, eliminating the need for bulkier bracing and once again ensuring a light roof structure, clean in appearance.
[float=left][attach]1225[/attach][/float]The distribution of the cablenet is also a safety factor should a particular cable ever fail. However, to ensure even force distribution, the cablenet had to be pretensioned. Due to the high degree of interdependency between the cables, it would have been extraordinarily difficult and time-consuming to tension each in turn without affecting the balance of the system, so the cablenet was designed to be self-tensioning. This was achieved by having each individual cable cut to an exact length, so that when the roof load was first applied to the cables, they would naturally reach equilibrium. The GSA analysis of the entire cablenet made this possible by providing the cable supplier with precise estimates of the forces acting in the almost 2000 cables. In case any section of the cablenet did not reach its correct equilibrium condition, turnbuckles were installed to adjust cable tension, but these proved unnecessary.
[b]Construction[/b]
The GSA model of the primary roof structure and cablenet was developed further to help the main contractor, Grocon Pty Ltd achieve a flat roof in the final condition. Structural analysis predicted the amount by which the roof would deflect once the steel rakers were filled with concrete, and the rakers were then given an initial upwards incline equal to this amount. The complexity of this task and the accuracy required was underscored by lack of margin for error: once the rakers were full of concrete, they would be too heavy for a crane to reposition.
[b]Conclusion[/b]
Despite the complex technical and scheduling factors, Melbourne's iconic Cricket Ground was transformed as intended into a state-of-the-art international sporting stadium and the focus for the 2006 Commonwealth Games.[/color]