In the past, this widely varying resource has created difficulties in trying to standardise glulam as a structural product. The milling procedure differs from mill to mill, and from species to species and the result has been that each producer has manufactured glulam of differing mechanical properties and of differing depths and widths. Designers were unsure of which properties and sizes were compatible, available and economic and the variance caused them problems in designing glulam.
As a result, the glulam manufactured by the GLTAA members has now been rationalised in order to establish a set of industry standard properties and corresponding sizes. The table below shows the GLTAA Glulam Mechanical Properties.
The designation of each group relates to the short duration stiffness (in GPa). The standard section sizes relating to each mechanical property group are available on request from members. These section sizes are the finished sizes of the glulam supplied. It is important for designers to note, that the correct designation be nominated on drawings, e.g. 315×85 GL18.
This makes the suppliers, builders, checkers and inspectors aware that the beam is to be an accredited section of known size and grade. It allows all producers capable of producing the grade of glulam to price the project without the designer having to make the decision to specify a one supplier product. The designation noted may be followed with a timber species if the designer requires a specific appearance. It should also be followed with a `C’ for cambered (600M Industry Standard Radius) or an `S’ for straight beams.
Producers nominated in their accreditation procedures which glulam properties they produce. The make up of the glulam may be in any configuration, so long as the grade and size of the glulam match that designated.