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On yer bike. . .

Working lives - Structural engineering

Two structural engineers are using their technical knowledge and experience to design mountain bikes.

Steve Melville and Andrew Cornett are structural engineers in the broadest sense of the description.

Not satisfied with daytime jobs designing exciting buildings, the two have spent the last four years designing and 'trialling' mountain bikes.

'We're both avid mountain bikers and felt that mountain bike frames didn't really satisfy us in terms of looks and manoeuvrability, ' says Melville, an associate director at Whitby Bird.

Melville and Cornett have jointly designed a mountain bike frame that is both durable and, they say, 'effortlessly stylish'.

This has been achieved by using structural engineering design principles, finite element computer analysis and a series of tests that involve pelting down forest tracks as fast as possible.

But their involvement also stretches to specifying materials, marketing the bikes and doing the accounts for their company, Pastey.

Since trading started at the beginning of this year the duo has sold around 15 bikes and their standard frame, the Pastey 'Howler', is receiving rave reviews from specialist magazines.

The 'Howler' is made from high strength steel, approximately five times stronger than that used for construction steelwork.

Cornett explains that because frames built from steel are able to flex more than those made of aluminium without failing, it is a better material for mountain bikes in terms of comfort and reliability.

'Strength is essential for a bike designed to be thrown around, ' says the Pastey website.

'Our understanding of materials from engineering also helped us decide on which material to use, ' says Cornett.

The mountain bike frame is a tubular steel truss which incorporates thicker wall sections in areas of high stress.

'The seat tube is thicker at the top than the bottom to take the eccentric load of the rider, ' says Buro Happold associate Cornett.

Finite element analysis was used to check the frame for tensile and compressive stresses and deformation. The result is a highly efficient lightweight steel structure.

Other design aspects are more mundanely practical: such as designing curves rather than angles to ensure mud does not accumulate on the bike frame.

The tubes are made in Birmingham 'so we can check the material quality, ' says Melville, and then shipped to Taiwan, the Mecca of bicycle frame making for assembly.

'We've gone through some abortive designs following advice from the Taiwanese manufacturer.

In some cases connection details have changed, ' says Melville.

The process is similar to the way structural engineering drawings are interpreted by fabricators and approved by consultants.

Melville and Cornett have also designed a titanium frame which is 15% lighter than the steel equivalent and will not rust. But at almost £700, it is also twice the cost of the steel frame.

The future for Pastey is to continue improving the basic frame design and to venture into the mechanical aspects of bicycle design.

In fact, any downturn in the construction market might be seen as a silver lining by Melville and Cornett, as it could give them the chance to concentrate on their joint passion for mountain bikes.

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