Investigation on the mechanical properties of open-hole spruce and douglas fir
Spruce and Douglas fir are the main materials of today’s modern wooden structure buildings. In wooden structure buildings, holes often have to be created on the building components in order to reserve channels for pipelines. At present, there are no detailed studies regarding the mechanical properties of these two kinds of lumber under open-hole condition. In this paper, universal mechanical testing machine was utilized to perform three-point bending tests on small samples of spruce and Douglas fir with open-hole (opening diameters being Ø13, Ø16, Ø20 respectively) and without open-hole. The bending strength and modulus of elasticity of openhole and no open-hole samples were compared, the effects of hole sizes on samples mechanical properties were analyzed and discussed, and the samples’ failure patterns and failure mechanisms were also studied. The experiments were loaded at a constant speed 5 mm. min-1 until the sample was broken, with the loading time controlled within 2 – 3 minutes. The results showed that: open-hole had significant impact on the bending strength of both kinds of lumber. In terms of failure modes, most of the Douglas fir samples were deformed only at the compression point before failing, while the Spruce samples not only formed grooves at the compression point but also cracked at the bottom. This indicated that compared with Douglas fir, the impact of open-hole on Spruce lumber was greater, thus open-hole should be avoided on Spruce components during construction. The experimental results provided a basis for future studies on the failure modes of these two materials and also the strength design of relevant components.