Trussing saves the joint

A radical metal jointing system which could halve the costs of building stadiums, public halls and hangars has completed its early development in Dundee University's department of civil engineering.

CATRUS is a development of the "space truss" system, a series of metal bars and joints creating a lattice arrangement which can support a roof, and is generally used to cover large open areas with few or no internal supports.

Project leader Ahmed Elsheikh, who has now lodged two patent applications, said: "Space trusses are usually chosen for constructions in which appearance is important. They look attractive, but the down side is that they are usually expensive - much more expensive than beamed and framed systems."

The Dundee team's aim was to produce very simple and cheap joints without compromising the strength and structural merits of traditional space truss systems.

"We have come up with a system that is not only around 50 per cent cheaper, making it more economical even than beamed and framed systems, but our tests show CATRUS is also stronger than conventional space trusses."

The secret, according to the Dundee researchers, lies in the simplicity of the joints. Much of the expense of conventional systems comes from joints which involve a substantial amount of costly welding and fitments. The system is made of short steel elements, called members, each of which requires node connectors, effectively spherical bolts, at each end. They require sophisticated machining.

But the Dundee system is based on much longer members spliced midway between the truss joints, which eliminates the need for traditional fitments. It uses no welding, relying instead on cutting and drilling, and is easy to make and assemble.

Tests on prototypes have also shown that while conventional systems are liable to collapse without warning when overloaded, CATRUS shows stress well before breaking point is reached. Struts buckle and warp, and the whole structure shows noticeable sagging, allowing repairs to be made.

Dr Elsheikh is currently seeking industrial partners to develop the research further. "The system is so simple. It has the potential to revolutionise the usage of space truss systems, opening up new markets where they would never have been able to compete before," he said.