An insight into mechanical properties of heartwood and sapwood of large French Douglas-fir LVL

Abstract

The French resource of large diameter Douglas-fir is currently still growing, while these large diameter trees are complicated to process efficiently by the sawmilling industry. The rotary peeling process appeared to be particularly adapted as an alternative to the usual sawing. This primary processing method produces veneers used to make a wood engineered product material called Laminated Veneer Lumber (LVL). The manufacturing process of LVL enables the distribution of the resource defects, allowing for increased mechanical behaviour compared to the solid wood from which it comes from. The main objective of this study is to provide an insight into the principal Douglas-fir heartwood LVL mechanical properties such as longitudinal and shear moduli of elasticity, bending, shear and compressive strengths. Up to now, there was no study on LVL derived from this resource. This study focuses on heartwood because of its very interesting natural durability properties for constructive outdoor applications. Moreover, a comparison with structural timber properties and a comparable industrial engineering product, made of Norway spruce and called Kerto® S was also achieved to place the material in terms of mechanical performance among the market. Globally, this Douglas-fir heartwood LVL showed high compressive and shear properties. Even though the bending properties were significantly lower than data from Douglas-fir LVL of the literature, they seemed appropriate for structural applications. A larger experimental campaign fully representative of the industrial process and dealing with larger samples will be needed to finally conclude on the characteristic values to be used in structural design.