A two-year research project at TRADA has resulted in the development of ‘new age’ flitch beams, made quickly and economically from UK resources, suitable for a variety of construction applications. Flitch beams are a composite made by sandwiching a thin steel plate for extra strength between timber sections. While the concept itself is not new, the TRADA project demonstrated for the first time that home-grown timbers (sitka spruce and larch) could be used. Furthermore, innovative fixing methods were used which have the potential to reduce the cost significantly.
Traditional flitch beams are made by bolting the timber and steel together through pre-drilled holes. In the TRADA project, the components were fixed with dowels shot-fired directly into the assembly with no pre-drilling. The method is fast and cheap so that flitches can be fabricated quickly from available resources.
Target markets for new age flitch beams include long span beams (viable because of the extra strength and stiffness given by the steel plate) for use in bridges, timber framing, post and beam construction, conservatories, portal frames and in situ restoration. Flitches are very versatile and so can easily be made, or cut to length, as required.
New age flitch beams have comparable strength and stiffness to imported timber composite beams, at a potentially lower cost. As well as providing a much needed, higher value outlet for home-grown softwood, dependence on imported structural timber composites can also be reduced.
In addition to laboratory testing for structural performance and durability, TRADA undertook a site trial. To demonstrate the speed and ease of on-site construction, project engineer Pia Larsen built a 5.1m span bridge on the TRADA site. The bridge comprises three flitch beams made up from two sections of larch, each 63x295mm with a 6x250mm steel core plate between. Pia fabricated the beams on site, shot-firing steel dowels in three rows. The hand rails are also larch, selected for its natural durability. Trials on methods of fixing the handrail posts included using shot-fired dowels to attach a metal bracket as well as more conventional fixings with threaded rods and nuts. To confirm stability, 23 of TRADA’s staff assembled on the bridge – the centre span deflection was less than 3mm.
The research project will go on to develop a calculation method for the design of flitch beams, although the quickest route to market is likely to be through third party certification of a standard range of sizes and nail patterns.
Andrew Abbott, managing director of TRADA Technology, said: ‘This is a first class example of the transfer of innovation into practice and how new products can be brought to market. It took an existing product and found ways of making it from indigenous raw material, cheaply and quickly. Manufacturers and merchants gain a UK-produced, marketable product and the construction industry has a new engineered structural product comparable with imports. We believe it will pave the way for other innovative solutions using UK-grown material.’
This year’s North East Coast Timber Trade Association student competition for structural design, which is run in conjunction with TRADA, will have additional special prizes donated by TRADA Technology for the use of new age flitches. Entries, which close on November 30, should be submitted via course tutors.
