Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect

Abstract

Finger joints in structural timber and glulam lamellae are often used to enable production of long members or to allow for re-connection of parts of a member after removal of weak sections. According to the European Standard EN 15497, certain margins are required between knots and a finger joint in structural timber, which means that a considerable amount of clear wood becomes waste when finger joints are applied. The purpose of this paper was to investigate the possibility of reducing the quantity of waste using different criteria for placement of finger joints. The investigation was based on (1) application of methods of colour scanning and tracheid effect scanning to detect knots and grain disturbance on board surfaces, and (2) interpretation of the requirements of EN 15497 regarding where finger joints may be placed. The standard's requirement when producing finger joints is that the minimum distance between a knot and a finger joint is three times the knot diameter. The standard allows for the minimum distance between a knot and a finger joint to be shortened to 1.5 times the diameter when the local fibre orientation is measured. Utilizing this in simulated production resulted in reduction of waste from 7.4 to 4.0%, when using finger joints simply to produce timber of long lengths. If finger joints are also used to re-connect parts of members after removal of weak sections, even larger savings can be made. Furthermore, it is concluded that knowledge of fibre orientation obtained from scanning could be used not only to decrease the waste in production but also to increase the quality of finger joints.

Quasi-brittle fracture and size effect of glued laminated timber beams

“…To apply these advanced wood material models successfully to timber, the internal morphology of timber needs to be known and modeled in detail, at least in the proximity of the governing defects. Promising research regarding the determination of the complete 3D orientation of the wood grain and approaches to model the complete morphology of timber is in progress (Guindos and Guaita 2013;Lukacevic and Fnssl 2014;Olsson and Oscarsson 2014;Jenkel and Kaliske 2014;Füssl et al 2014). These approaches which in a figurative sense model "the wood within the timber" might improve the knowledge of the effects of defects in the near future.…”

11th Hardwood Conference Proceedings

“…This name derives from the first observations on softwoods (Nyström 2003) (Simonaho et al 2002) and , which is based on the anisotropic scattering of concentrated laser light projected onto the wood surface (Daval et al 2015;Purba et al 2020) . (Olsson et al 2019) and (Besseau 2021) suggested using fiber orientation measured from such scanners to ensure the finger-joint strength rather than knot diameter (d) or distance to knot. Both authors offering promising prospects for reducing material waste and improving the reliability of finger-jointed lamellas.…”

“…Both authors offering promising prospects for reducing material waste and improving the reliability of finger-jointed lamellas. (Olsson et al 2019) defined a threshold of 8° to determine quantitatively when fibers are "approximately parallel to the axis of the board" as it is stated in (NF EN 14080 2013) standard. They found out that wasted material when cross-cutting Norway spruce can be decreased from 7.4% to 4% when applying a rule based on a minimum distance of 1.5 times d from the knot and a fiber deviation below 8°.…”

Modelling and Multi-Objective Optimisation of Finger Joints: Improving Flexural Performance and Minimising Wood Waste

“…For example, according to several experiments on the flexural behaviour of CLT panels conducted by Navaratnam et al [6], finger joint failure is one of the most common failure modes observed in the tests. As a result, several design factors related to finger joints such as finger length, tip width, pitch, and finger slope should be considered in the production of an EWP to assure its structural performance [6][7][8]. Several studies have been conducted to investigate the effect of finger joint design parameters on structural performance by performing experiments or using the finite element method (FEM).…”