GREEN OAK BUILDING WITH HIGH-TECH METHODS, PART 2: LOG BENDING TESTS FOR DETERMINATION OF STRENGTH AND STIFFNESS

Abstract

The green oak building research project deals with small-diameter oak logs as sustainable construction material for timber truss structures. The basis for structural use and design are the specific mechanical properties and the knowledge of performance influencing factors like wood defects, moisture content and density distribution. In a first step, the characterisation of the raw material itself has been done by quality assessment, followed by the determination of strength and stiffness parameters as input for the parametric design process and a prototype building as proof of concept. This paper summarises the experimental investigations on strength and stiffness of naturally dried green oak logs. The laboratory tests were supplemented by non-destructive data acquisition of the geometry, moisture, and density distribution along the full length and over the entire surface. The results show that strength and stiffness properties are affected by growth conditions, especially the moisture content and drying behaviour of green oak. The obtained results were in line with similar tests on softwood logs and other studies comparing destructive and non-destructive mechanical characterisation methods for roundwood. The preliminary results of the green oak research project indicate that small-diameter oak logs (≤ 250 mm) appear suitable for load-bearing timber structures.