Risk of extension of Hylotrupes bajulus attack in glued laminated timber

IRG/WP 278

M-M Serment

Although efficient work-methods and maintenance procedures, which prevent the wood from becoming damp and are therefore successful in considerably reducing and even in excluding the risks of decay, such methods are ineffective in eliminating the risks of infestation and destruction of timber by the House Longhorn Beetle, Hylotrupes bajulus, the chief enemy of softwood timber structures. The possible treatment of glue-laminated timber frames has only been systematically studied for the last few years and is generally limited to the surface application of organic solvent type preservatives. In most cases, this treatment is carried out at the factory before final warnishing takes place. The aim of this paper is not to discuss this type of treatment, which would require certain reservations. As many untreated timber frames have been erected and since in the majority of those which are currently being erected, cracks - ideal sites for the House Longhorn Beetle to lay its eggs are discovered chiefly during the first year, its seems pertinent to examine the dangers of increased infestation in this type of structure and the need for eradicant treatment; in other words, to examine wether successive laminates or ultimately the entire beam will be affected if one infested laminate is incorporated into a particular structure or whether infestation will remain confined to the initial laminate. We shall need to determine whether the larvae of Hylotrupes bajulus are capable of penetrating the various types of glued- laminated timber. By gluing together thin layers of wood of limited length, the technique of glued laminates aims at manufacturing wood products which are both thick and of great bearing, but which proportionally have only slightly less mechanical strength than the same piece of solid wood. There are two types of assembly: 1) by gluing together laminates lengthwise, so as to produce beams of given thickness, and 2) by gluing together end-grain surfaces of laminates so as to produce beams of a given length. Both types of assembly are included in the diagrams accompanying this paper. The possible penetration by larvae of the House Longhorn Beetle have been studied in the case of each type of assembly. It is also known that the larvae of this species are capable of penetrating various kinds of relatively hard substances. In this respect, larvae at various stages of development can behave in different ways for tunnelling capacities. Hence the experiments described below have been carried out with two types of larvae: newly hatched larvae and larvae of medium size.


Keywords: FINGER-JOINTS; GLUES; INSECTS; HYLOTRUPES BAJULUS; LARVAE; LAMINATED TIMBER; PINUS SYLVESTRIS; RESORCINOL; UF-RESIN

Conference: 77-09-26/30 Noordwijk aan Zee, The Netherlands


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