AUS vs imported glulam marking/labelling

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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

GL8

GL19

GL10

GL22

GL22, GL24

GL12

GL25

GL26, GL28, GL30

GL13

GL33

GL32

GL17

GL40

GL18

GL45

 

Table 2: Strength and Stiffness Comparison

AS/NZS

EN

(h - homogenous glulam)

GL10 (Relabelled as GL22)

GL20h

f'b = 22 MPa, E = 10GPa

f'b = 20 MPa, E = 10.5GPa

GL13 (Relabelled as GL33)

GL28h

f'b = 33 MPa, E = 13.3GPa

f'b = 28 MPa, E = 12.6GPa

GL17 (Relabelled as GL40)

Not available

f'b = 40 MPa, E = 16.7GPa

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.

Glulam

Glulam, short for glued laminated timber, is an engineered wood product manufactured by gluing together pieces of timber, known as laminates. This process produces larger size and longer length members, which can be curved or straight.

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