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MuseumsCivic Steel trusses of up to 64m span at differing slopes form a hyperbolic paraboloid roof surface. two directions. Although the finished structure will 90% of their capacity. The asymmetrical portal be characterised by these spectacular sweeping frames are stabilised by the spine walls at the curves, clad in silver, every structural element is gables, while the roof planes are braced by two straight. large compound trusses. Fully welded joints at the On plan the design provides 6,320m2 of top of the main roof trusses and pins at the bases exhibition space in two triangular areas which ensure they are acting as portal frames, except will be divided by a central walkway, representing at the ends where the trusses bear on the vertical a world divided by ideology. Aircraft will be spine walls. displayed both on the floor and suspended from With the design finalised, the team called in the roof. steelwork contractor SH Structures to help out “After we had decided on the concept of an with the buildability issues and to confirm that the asymmetric double curved roof we had two structure could be built within the budget. One key problems: how to analyse it and how to build it,” issue still to be decided was the cladding — and says Mr Brady. how to fix it. The designers opted for a proprietary For the first stage of the analysis the team turned structural metal decking spanning between the to a consultant specialising in wind engineering. trusses, with the aluminium standing seam system “As there was no precedent for this building we fixed on top, but had not worked out exactly how to commissioned a scale model and wind tunnel fix the metal decking to the structural sections. test,” explains Mr Brady. The results were fed into “We knew the main steelwork was going to be a 3D model built using the Robot program, which made from circular hollow sections, and that these allowed the engineer to do a complete analysis of would have a constant diameter but different wall the entire frame. The analysis involved more than thicknesses depending on the load they take,” 450 different load cases including wind, snow and says Peter Redfern, Estimating Manager for SH the weight of aircraft suspended from the roof. As Structures. Mr Brady says: “This building couldn’t have been The challenge was to come up with a detail to done without a 3D analysis package.” fix the structural decking to the circular hollow The analysis showed that the structure is very sections. The varying pitch of the trusses means efficient, with most elements at between 85% and the decking meets each of the top chords at a NSC October 2005 15


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