Strength calculation method of timber beam with two holes

Now, there are the needs of the utilization of timber structure to the non-housing buildings. It needs the several techniques without the conventional wooden structure techniques. The multi story wooden structures having long span need the technique of making large holes in the beams due to the pipe arrangement of the equipments. We, in this article, propose a manual strength calculation method of the timber with two circular holes taken into account the size effect, the hole size, the distance between the both holes, and the ratio of the bending moment and shear force as the parameters. Two failure modes was assumed, the shear failure of timber between the both holes, and the splitting fracture from the hole. From the experimental observation, the shear failure was occurred in the specimen having the short distance between the holes -less than 0.5 times of the hole diameter. And splitting fracture was occurred in the specimen having the long distance between the holes -over 0.5 times of the hole diameter. The calculation method was derived from the mechanical models based on fracture mechanics and basic beam theory. The validity of the proposed calculation method was confirmed by the experimental results whose parameters were the hole size, the size effect, and the distance betweenboth the holes.