GLUING OF EUROPEAN BEECH (FAGUS SYLVATICA L.) AND DOUGLAS FIR (PSEUDOTSUGA MENZIESII Mirb.) FOR LOAD BEARING TIMBER STRUCTURES

摘要

Facing new wood species for the production of glulam, bonding of those species is becoming relevant. Due to certain advantages of European beech and Douglas fir, enhanced glulam consisting of these species can be produced. An essential requirement for the production are adhesives that guarantee durable and reliable bonding. In Europe, the most important type of adhesive for the production of glulam are MUF resins. To avoid frequent changes of adhesive systems during production, MUF systems are required that allow for reliable bonding of Norway spruce as well as Douglas fir or beech. One goal of this investigation was to describe to what extent two commercially available MUF-adhesives can be used for gluing beech and Douglas fir. With regard to the requirements for technical approval of beech glulam, the resistance to delamination according to EN 302-2 was chosen as test method. As beech wood often shows a natural variation of heartwood (red heartwood) this was also taken into consideration.Since glulam manufactures have the choice between delamination and block shear test within factory production control, this study also aimed at verifying the assumed correlation between the two tests. Additional studies were carried out to examine the delamination test more closely. This appears to be obvious since different characteristics in swelling, shrinking or drying of wood species influence the test results. These differences have an impact on the generated critical tensile stresses to which the glue line is exposed. This study also contributes to an ongoing discussion in Europe concerning the suitability of the delamination test for wood species with higher density.Based on the results of the delamination tests, another approach was to describe gluing characteristics of the wood species involved. Understanding the specific interactions between different wood species and adhesives is an important contribution to enhance bonding of those species. Although curing is veryimportant for the development of a bond, it is not well surveyed. Therefore, this study also pays attention to the curing behaviour depending on the characteristics of the wood species. As a reference all tests were also carried out for Norway spruce.