Embedment Strength of New Zealand Cross Laminated Timber

The design of timber beams and joists is often governed by serviceability requirements, i.e., meeting deflection limits over the life of the structure. Since timber is a visco-elastic material, it is subjected to creep when permanent loads are applied. The amount of creep depends on several variables, e.g., load-to-grain angle, moisture content of timber and stress level, which therefore strongly affect the design. This paper presents an overview of the creep properties of timber, including conceptual models of the material, constitutive laws, and analytical approaches proposed by current building codes. The purpose is to provide a link between the advances in terms of experimental results and theoretical formulations to common design calculations. Redirections to the most relevant studies are reported for the reader interested in a more comprehensive knowledge of each specific topic. Finally, the long-term deflection of a Radiata Pine LVL beam calculated by four different procedures specifically according to New Zealand Standard 3603, Eurocode 5 (European code), National Design Specifications for Wood Construction (North-American code) and Torattiā€™s model is reported. The aforementioned models seem providing consistent results, however the uncertainty in the deflection estimation appears growing in case of more extreme environmental conditions. These discrepancies are believed dependent on how each procedure takes into account the mechano-sorption effect.

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