Bending Strength and Stiffness of Glulam Beams Made of Thermally Modified Beech Timber

Abstract

The paper describes tests carried out on structural glued laminated timber (glulam) beams and finger-jointed boards made out of thermally modified hardwood (beech, fagus sylvatica) in the following named as TMTB. The finger joints were bonded with a two-component PRF adhesive and the lamellas were edge-bonded using a two-component MUF adhesive. The finger jointed lamellas were tested in tension, flatwise- and edgewise bending. While automatically produced finger joints mostly showed unsatisfactory strengths, it was possible with manually produced finger joints to achieve higher strength values. Fifty glulam TMTB beams were produced to evaluate their load carrying behaviour. The beams were tested in 4-point bending and the integrity of the glue lines was verified by means of delamination tests and shear tests. Usually it is expected that combining lamellas of a certain strength class to a glulam beam will enhance certain characteristic mechanical properties of the final product compared to the properties of single boards. The results of the tests could not confirm this behaviour for the TMTB glulam beams even if the bond lines proved to be of a satisfactory quality. Hence, a structural use of TMTB glulam seems to be restricted to a limited range of applications.