Construction industry stresses
The word glulam, for glued laminated timber, has entered the architects' lexicon. Unlike, say, PFB for parallel flange beam, it is understood instinctively by its abbreviation only. First used in Basel in 1893, glulam technology was advanced in the interwar period with the development of waterproof synthetic resin glues in the American aircraft industry. During the past 50 years or so, glulam has become a mainstream material for architects wishing to marry structural support with the elegance of timber.
However, new research at the Welsh School of Architecture into low-tech timber laminates could see the cost of such laminates come down by simplifying production for limited applications.
The researchers suggest using local labour in areas where glue laminating is not readily available. The 'stress-lam' system is a dry timber construction process that uses small sections and lengths of locally grown timber, such as Douglas fir, Sitka spruce and larch, in prefabricated panels to construct building components, such as walls, floors and roofs replicated as a 'table'. The simplicity comes from creating structural stability by generating friction between small lengths of timber, using bolts, cables or even rope.
The test table is made of 50 x 100mm sections of sycamore lamellae in panels 2.4m and 1.5m long to create interlocking fingers. Bolts pierce adjacent panels through the full width of the table, using M12 stainless steel studs, bearing plates and 19mm nuts at 600mm centres. The table top was constructed in five unglued pieces to test the ability to prefabricate the system in situ. Lengths can be carried into position, slotted together and held in place.
Each lamella on the table top has been tongued and grooved to help resist some of the torsional movement, but predominantly this just helps register the lamellae with one other so as to provide a relatively smooth surface.
The rotational movement around the connections has been counteracted primarilyby the stress and friction generated between the lamellae, therefore effectively making the table top act as one large slab of timber 100mm deep.