Timber products available on the Australian market are either manufactured in the country or imported from various parts of the world. Differing overseas product marking/labelling requirements may create confusion within the Australian building and construction industry, which uses these timber products.
In this article, WoodSolutions aims to clarify the marking/ labelling of structural glued laminated timber (glulam) as per AS/NZS and European GL grades.
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.
In the case of marking/ labelling of glulam products, there may be confusion regarding the meaning of the numerical value in the GL’X’ descriptor. Both Australian and European products mark/ label structural glulam products using a GL prefix followed by a numeric 'X' value; however, the ‘X’ value refers to a different structural property in each system:
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).
WoodSolutions has illustrated this difference in approach through two tables: While one table shows a ‘relabelling’ of AS/NZS grades using the EN method, the other presents 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.
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 offered by a supplier is not manufactured in accordance with AS/NZS 1328.1 Glued laminated structural timber – Performance requirements and minimum production requirements, ensure that the grade proposed has the structural engineer’s approval. To explain this difference in labelling, a note has been proposed to be incorporated in AS/NZS 1328.1.