The world shortage of structural steel is forcing contractors to consider constructing the floor structures of offices and high-rise residential apartments from concrete.

A spokesperson at trade body the Concrete Centre said: “The rise in cost of steel frames has led to designers looking at alternative frame solutions, including post-tensioned concrete, for floors of office buildings.”

The cost of structural steel has risen 50% since the start of the year. The current price is £1400 a tonne, with hollow sections costing up to £3500 a tonne. A further rise in steel prices of £50 a tonne is expected in January.

The total floor area constructed using post-tensioned concrete has increased from 370,000 m2 in 2002 to 650,000 m2 in 2004. The Concrete Centre spokesperson said that the growing use of post-tensioned floors would continue “for some time yet because they use less steel than conventional reinforced concrete floors”.

The soaring price of steel has led to steelwork subcontractors insisting on a fluctuating prices arrangement, rather than being tied to a fixed price, making it difficult for contractors to offer fixed-price contracts.

The rise in cost of steel frames has led to designers looking at alternative frames

Concrete Centre spokesperson

There are reports that some of the larger contractors are pre-ordering 1000 tonnes-plus orders from the rolling mills at predetermined prices. However, most contractors do not have steel orders large enough to benefit from pre-ordering and so are at the mercy of the market. Instead they must resort to alternatives such as post-tensioned concrete structures to win work.

Post-tensioned concrete flooring has been used in America and Australia for more than 40 years. Until now the quick deliverability and design flexibility of steel has favoured it over concrete solutions for the construction of offices in the UK.