Gluing of European beech wood for load bearing timber structures

The load bearing capacity of glulam could be enhanced by using lamella of European beech (Fagus sylvaticaaEuro-aEuro-L.). Essential requirements for the production of those beams are adhesives which allow for a durable und reliable bonding of lamella. The paper shows to what extent commercially available MUF and PU adhesives and adapted bonding parameters ensure gluing of European beech timber for load-bearing timber structures. Both beech wood containing heartwood and beech wood without heartwood were included in the study. With regard to technical approval, the chosen test methods were resistance to delamination according to ENaEuro-aEuro-302-2 (2002) and shear test of glue line according to ENaEuro-aEuro-392 (1995). From the two tested MUF systems it was evident, that delamination decreased by increasing the closed assembly time. The requirements of ENaEuro-aEuro-301 (2006) were fulfilled for adhesive typeaEuro-aEuro-I andaEuro-aEuro-II. Without any limitations beech wood containing heartwood could be glued using MUF-1. On the other hand, the results of the PU adhesive were insufficient. Light-optical micrograph examinations show that long assembly times secure the formation of a glue line. It was assumed that the curing process is retarded by beech wood. No relationship was found between the results of the shear strength test and the delamination test. For quality control of glulam the delamination test is recommended. Based on the positive results an application for technical approval of glulam consisting of beech was made. For this reason beech-glulam can be generally utilized in service classaEuro-aEuro-1.