Mechanical properties of strip-like laminations made from hardwood

Abstract

The European Union pushes for a higher share of wood-based materials in the building sector. Consequently, making sufficient volumes of high-quality wood available is a major concern. Climate-driven forest conversion leads to an increasing share of hardwood trees in Central European forests. The use of hardwood species is currently uncommon in the building sector as hardwood species are not sufficiently covered by European standards for timber structures. In addition to this, lower material yields and increased tool wear are common in hardwood processing. Furthermore, grading hardwood species comes with major difficulties, leading to even lower yields and an assignment to strength classes worth improving, as only parts of the material can properly be assigned to strength classes. To substitute the board-based grading approach we produced a semi-finished product, “strip-like lamination” (SLL). Preselected, low-grade sawn hardwood from European beech (Fagus sylvatica) and oak (Quercus spp.) was used as raw material for the SLLs. Each lamination consists of multiple “strips”, stemming from different hardwood boards, mitigating the strength-limiting effect of various wood characteristics in these SLLs. This work provides the first comprehensive mechanical performance profile for SLLs from beech and oak including the finger joint performance. Furthermore, we show the extent of the desired homogenization of the raw material through non-destructive testing. The mechanical properties of beech SLLs exceed the requirements for European softwood strength classes. The results show great potential for SLLs in structural applications. SLLs should complement strength-graded structural timber in structural glued wood products, like glued laminated timber (GLT) and cross-laminated timber (CLT).