Influence of wood properties and bonding parameters on bond durability of European Beech (Fagus sylvatica L.) glulams

Considerable progress has been made recently to promote glue-laminated beams of European beech (Fagus sylvatica L.) for load-bearing structures in engineering. However, further investigations into the bond durability are required. The objective of the present study was to analyse material and manufacturing factors and their combination to improve the resistance in delamination tests as required for the use in building service class 1. In the experimental work, the influence of selected wood properties, manufacturing conditions, and the effect of a hydroxy-methylated resorcinol primer on the delamination resistance of beech glulams bonded under laboratory and industrial conditions with amelamine-urea-formaldehyde adhesive were investigated. The highest delamination resistance of the laboratory samples was achieved with the smallest lamellae thicknesses of 29 mm. A closed assembly time of more than 30 min and the use of the primer further enhanced the bond durability. Higher delamination rates observed in glulams manufactured industrially were related to the relatively thick (38 mm) and often twisted beech lamellae used. The results suggested that bond durability required for service class 1 can be attained by restricting lamella thickness in beech glulam to a maximum of 30 mm and by using a minimum closed assembly time of 40 min.