British Steel breakthrough claim

British Steel is launching what it describes as the most significant innovation in steel construction for more than 40 years.

The revolutionary new flooring system, known as Slimdeck, combines the world's first hot rolled asymmetric beam (ASB) and an advanced floor decking system, SD225, a deep composite metal deck design.

The Slimdeck flooring system will be unveiled on 13 May at the National Steel Construction Conference in London. British Steel believes it will significantly enhance its competitiveness against other materials in the construction industry on multi-storey buildings and help reduce construction costs and times.

Slimdeck has an increased fire resistance and simplifies M&E service integration. The increased stength and lightness of the system reduces the overall floor zone thereby allowing more floors to be fitted to multi-storey buildings.

The asymmetric beam is up to 25 per cent lighter than BS's previous Slimflor beam. The reduced weight of the beam aids on-site fabrication and speeds up construction times. The beam comes in three sizes.

The new beam has an embossed diamond pattern rolled on to the top flange, which enhances the composite action between the beam and the in-situ concrete over the top flange of the ASB - thus eliminating the need for welded shear studs.

The beams have a thicker web than flange to achieve good fire resistance properties. The thicker web also enhances the section's torsional properties. The system has a 60 minute fire resistance and the deck elements help prevent concrete spalling.

To get the best thermal properties 60mm of lightweight concrete or 70mm of normal concrete are needed on top of the beam. The shape of the deck and thermal capacity of the slab provide simple options for natural ventilation, night-time cooling and air circulation within the troughs.

The SD225 steel decking system has been developed for use with the new beam. The British Steel team had to do its own bending resistance tests. SD225 has a greater load carrying capacity, a longer span range and improved ceiling fixings and service integration capabilities compared to current decks. The Slimdeck system allows unobstructed space directly below the floor slab. Extra ceilings or services can be hung from the sidelines.

In addition the SD225 deck is designed to allow extensive service integration into the trough, thereby reducing construction depths. Services can also be passed through the ASB via holes which can be cut either at the factory or on site. The holes can be up to 160m diameter if round - or half as much again if shaped as flat ovals. This allows unhindered service runs across the whole length of the floor, though it does not allow for transverse connections.

The ceiling may be fixed immediately below the ASB soffit thereby achieving an overall floor zone of around 400mm. This cuts building height to a minimum and saves costs. With this sytem, the Canary Wharf tower in London could have been reduced in height by 15 per cent while retaining the same number of floors or could have gained an extra floor for every eight.

The asymmetric beam was developed under a œ1.2 million research programme 50 per cent funded by the DTI's LINK Enhanced Engineering Materials Programme. British Steel's research partners were the Steel Construction Institute, the University of Sheffield and the University of Cambridge.