Glued Laminated (GL) Structural Timber Product Marking/Labelling - AS/NZS and European GL grades
The Australian building and construction industry uses a wide range of timber products manufactured in Australia as well as imported from all corners of the world. Sometimes confusion may result in the Australian marketplace due to differing overseas product marking/labelling requirements; a potential for such confusion is the marking/labelling of structural glued laminated timber (glulam).
It has been reported that the availability of European structural glulam products in the Australian market may lead to confusion when simply looking at the marking/labelling of glulam products regarding the meaning of the numerical value in the GL“X” descriptor. Both the Australian and European products mark/label structural glulam products using a GL prefix followed by a numeric 'X' value but refers to a different structural property in each product respectively, as follows:
- In the Australian/New Zealand (AS/NZS) system, the “X” refers to the bending stiffness (modulus of elasticity) in gigapascals (GPa)
- In the European (EN) system, the “X” refers to the bending strength in megapascals (MPa)
To illustrate this difference in approach, Table 1 shows a “relabelling” of AS/NZS grades using the EN method and Table 2 shows a selective comparison between AS/NZS and EN grades in terms of their respective bending strength (f'b) and stiffness (E) (modulus of elasticity) values.
Table 1: GL Grade Comparison
AS/NZS GL grades based on stiffness
AS/NZS GL grades if "relabelled" using the EN system
Typical EN Glulam Grades
GL26, GL28, GL30
Table 2: Strength and Stiffness Comparison
(h - homogenous glulam)
GL10 (Relabelled as GL22)
f'b = 22 MPa, E = 10GPa
f'b = 20 MPa, E = 10.5GPa
GL13 (Relabelled as GL33)
f'b = 33 MPa, E = 13.3GPa
f'b = 28 MPa, E = 12.6GPa
GL17 (Relabelled as GL40)
f'b = 40 MPa, E = 16.7GPa
GL18 (Relabelled as GL45)
f'b = 45 MPa, E = 18.5GPa
In Australia, engineering designs are undertaken in accordance with AS1720.1 Timber structures Part 1: Design methods, unless otherwise stated by the structural engineer, using the defined timber structural grades/properties. If a structural glued laminated timber product is offered by a supplier not manufactured in accordance with AS/NZS 1328.1 Glued laminated structural timber – Performance requirements and minimum production requirements, check that the grade proposed is acceptable by the structural engineer. To explain this difference in labelling, a note has been proposed to be incorporated in AS/NZS 1328.1.