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Stretch a case

Letters

I read Clean bill of health regarding use of steel frames for hospital building (NCE 15/29 December 2005) and write to draw your readers' attention to additional information. The thinnest structural form that meets vibration criteria is a post tensioned concrete flat slab.

An independent Arup report has demonstrated this and it is available at www. concretecentre. com.

To meet vibration criteria, a combination of mass and stiffness is required.

With concrete you get this performance at little or no extra cost. Why pay for the significant extra mass and stiffness needed to improve the performance of lightweight solutions?

Hospitals do require flexibility built into their designs as stated in your article. The most effective way to provide this is to have flat soffits for maximum flexibility of services during design, construction and operation.

Do not assume flexibility is provided by long spans (whether concrete or steel).

Long spans are rarely needed in hospitals. The room layouts do not require them.

Long spans can, in fact, have a negative impact. The downstand beams reduce flexibility for services and increase the cost and time to seal partition heads. This latter point is significant, given the huge length of partitions, and can represent a 10% increase in the cost of partitions.

Andrew Minson, head of framed buildings, Concrete Centre, 4 Meadows Business Park, Station Approach, Blackwater, Camberley Surrey, GU17 9AB

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