Salt Lake City's new Olympic speed skating rink is pushing construction technology to its limits in the search for the 'fastest sheet of ice in the world'. Words and pictures by Adrian Greeman.
A host of speed skating world records fell at the 1998 Winter Olympics in Japan, mainly because of a new 'collapsible' blade that lets sprint skaters hold curves better. Salt Lake City wants to top this when it hosts the next Winter Olympics in 2002, beating what is currently held to be the 'fastest ice' in the world at Calgary's enclosed speed rink.
The challenge is mainly technological. Producing even ordinary skating ice involves more than freezing a shallow pool of water; it is instead built up in hand-sprayed layers and then 'shaved' to flatness with special machines, known as Zambonis.
For speed skating a host of other critical factors come in. The ice must be flat beyond even the tolerances used for so-called 'superflat' warehouse floors, which means the supporting slab below must be incredibly flat concrete, with no irregularities.
'The level must vary no more than 2.5mm over 3m,' says local architect Gillies Stransky Brems Smith partner David Brems. 'No point on the 200m long areas must be more than 6mm above or below any other.'
Ground below the slab could heave from permafrost build-up, so contradictorily the slab is heated underneath its freezer tubes. There must be no 'soft spots' caused by even minor temperature variation in the ice, or differences between race lanes which could invalidate event times.
'That means the coolant circulation must have no irregularities' says Brems. 'It also affects the air conditioning, which must maintain even temperatures and cope with keeping a 6,500 strong audience comfortable without affecting the rink ice.'
As if that was not challenge enough Salt Lake City wanted a budget price facility. 'Japan went almost to $300M (£187.5M) for its Nagano Olympics speed rink,' says Salt Lake Olympic organising committee member Ranch Kimball, director of construction for the permanent venues. 'I can tell you this facility will cost just $28M (£17.5M).'
This target has been met partly by building the facility on the site of an existing outdoor rink some 10km from Salt Lake City. The existing rink's freezer plant will be retained as the core of the new coolant system.
But more important is an unusual 'suspension' structure for the new building, devised by the New York office of Ove Arup, which has been working as part of a multidisciplinary team alongside the architect and local structural engineer Martin & Martin. Arup is also responsible for M&E design.
There are 12 masts either side with a cable slung between each pair, like a 100m span suspension bridge. The lattice towers, raked back at 10degrees, are anchored by vertical tie cables to clusters of five 300mm diameter steel tension piles rather than traditional anchor blocks.
'The design emerged from a comprehensive look at a dozen options,' says Ove Arup senior project engineer Ignacio Barandiaran, 'Including long span trusses, tied arches and a cantilevered truss, as well as prefabricated industrial sheds. But when non-structural factors like air conditioning were included, the suspension design came out cheapest.'
The suspension system allows the use of very shallow roof girders, just 900mm thick, minimising roof space and therefore the air mass to be cooled in summer.
It is vital for the building envelope to be complete before work starts on the 170mm thick slab. Wind, temperature change and drying effects on concrete must be minimised. Nothing must disrupt the accurate placing of top and bottom reinforcement, and the network of coolant pipes must be spot-on.
'We have seen on another project how the steel bar chairs can get knocked over by small temperature changes,' says Salt Lake City-based main contractor Layton Construction Company project manager Mike Sears. Layton is currently forming boundary walls, pylon foundations and a tunnel which runs underneath the centre of the 400m long speed oval.
This allows access to two hockey pitches in the centre of the oval, explains Brems, as well as a route for main coolant and power lines. Its structure needed thought because of possible differential settlement between the tunnel and the surrounding backfill: special concrete 'wings' cantilever out either side at the top over the vulnerable area.
But everyone is getting excited about the big pour in June, the most critical operation. Even thinking about the concrete design has meant months of agonised debate. There must be no cracks or shrinkage, which means small aggregate and a slow cure with a high proportion of Portland cement in the mix replaced by pulverised fuel ash.
Yet the mix must flow and even be pumpable. It must settle in around a slab chock full of reinforcement top and bottom, and a network of 40mm diameter coolant pipes for brine at 100mm centres in between.
'And there must be no voids because these not only have a structural effect but they also cause thermodynamic irregularity,' says Martin & Martin site engineer Steve Judd. He jokes that the final mix design has 'negative slump' with a low water content to reduce free water shrinkage. Mid-range and high range water reducing admixtures are essential.
Cold joints will be completely unacceptable so a special sequence is needed for the estimated six hour, 1000m3 pour. Two crews will begin on one side of the oval and work away from each other around the ring until they meet on the far side. Layton will use a special rolling screed for the finish and the hope is crew movements in the slab areas will be kept to a minimum. Coolant pipes will be air filled and any leaks will be instantly visible.
Why read this
Advanced slab design deals withrapid freezing demands
Leading edge concrete technology produces superflatsurface
High tech cable stay structuresaves millions of dollars