ALTHOUGH something of a novelty in the UK, DeltaBeam construction is well established in Scandinavia , The Netherlands, Germany and Austria.
The idea was developed from the steel 'top-hat' profile, a lightweight hollow steel section commonly used in composite construction. 'We thought we could do better, ' says Teraspeikko managing director Raimo Lehtinen. 'We wanted to use the composite action of steel's tensile strength and concrete's compressive st reng th and we also wanted to minim ise construction heights. We have achieved that with the flat soffit.' DeltaBeams are hollow welded steel beams, trapezoidal in crosssection and pierced with holes down both sides. Welded inside the bottom f lange of the beam are lengths of reinforcing steel.
At Drake Circus the DeltaBeams are bolted onto steel connectors cast into the tops and bottoms of the precast concrete columns. The floors comprise standard concrete hollow-core planks from Bison Structures The ends of the Bison planks sit on the DeltaBeams' thin bottom flange and reinforcement is threaded through the holes in the DeltaBeam before the whole assembly is filled with concrete. Finally, a 100 mm thick structural topping is cast on top of the beams and planks.
The finished floor is a flat, smooth structure with only the exposed bottom flange to indicate the posit ion of each DeltaBeam.
Drake Circus is the fifth UK project to make use of DeltaBeam since it was introduced here by BRC in 1998. Drake Circus will incorporate 9.6 linear km of DeltaBeam. The largest project so far ? a hospital in Sweden ? consumed 12 linear km.