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Engineers go in at full blast

DESIGNING MILITARY fortifications must be one of the most frustrating areas of civil engineering. No sooner have you devised a structure that can resist the enemies' most powerful weapons than they develop a new weapon to beat it.

But this also makes military engineering one of the most challenging and exciting disciplines. This was the message of a recent lecture at the Royal School of Military Engineering in Chatham. Engineers from the Corps of Royal Engineers, defence research centre DERA and steel manufacturer Corus gave a joint presentation of a new modular system for constructing bomb resistant structures developed for use in Northern Ireland.

RE project manager Major Laurence Quinn MBE first came up with the concept for the Redline system in 1994 to protect army facilities from car bombs and mortars. Until then, army buildings were protected by heavy concrete walls with steel plates fitted to the internal face to prevent concrete flying off during an explosion.

To increase the efficiency of the structures, the Sappers' Northern Ireland design office connected steel plates at the back of the wall to the front face reinforcement. The composite strength of the concrete and steel sandwich meant smaller sections could be used.

But the insitu welding and casting required meant workers were vulnerable to attack for dangerously long periods. So in 1996 the REs set out to develop a modular version that could be constructed more quickly.

The result was Redline MkII - composite steel and concrete panels that slot between steel I-section uprights and cross beams to make a solid wall.

Each 3m wide steel panel uses two flat steel sheets connected on three edges by a steel fillet to form an open envelope. Steel loops are welded to the inside of each face and bars slotted through the loops. The panel is then filled with concrete.

The panels are fitted into precast concrete bases and steel uprights on site and cross beams fitted across the top.

The ability of the panels to act in unison is key to its strength. Head of DERA's fortifications section Fred Hulton explained that most of the damage from a bomb blast is caused by a single, fast moving energy wave and if a structure is able to absorb this it will withstand the explosion. In the Redline system the panels connect together to work as a large single mass, he added.

Hulton explained that if the wall could also yield without tearing, like a balloon swelling, the tensile membrane action would absorb the blast energy.

Major Gareth Jones who devised the Mark II said the panels could be fabricated off site with construction time five times faster than the MkI.

Major Rob Blackstock said REs were researching the possibility of reducing costs further with Bi-Steel panels designed for the North Sea.

These also use composite action of two steel plates around concrete but are connected with circular steel rods friction welded between the plates.

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