木材のスパン−ハリタケ比と曲げ特性との関係

This paper deals with the characteristics of bending strength i. e. the modulus of bending rupture, stress value at propotional limit, shearing stress and the modulus of elasticity in bending, when the span-to-depth ratio of wooden beam is varied from 2 to 20. In case of a simply supported beam that carries a concentrated load P at midspan, as Figure 1 indicates, the results of the experiments are shown in Figure 2 through 5.
On the basis of the results, it can be concluded as follows :
(1) Figure 2 illustrates the similar tendency to the modulus of bending rupture between HINOKI and RED LAUAN, except that the span-to-depth ratio of 6 of HINOKI beam makes a maximum, that while that of RED LAUAN does not show the maximum. It demonstrates, furthermore, such a phenomenon of the modulus of bending rupture is affected by the compressive strength perpendicular to grain, and by species, etc.
(2) In Fig. 3, it can be seen that the stress at proportional limit of bending increases as the span-to-depth ratio of beam increases, and a single curve is drawn through all of the points to emphasize the similar behavior of HINOKI and RED LAUAN beams tested. The author can infer that the span-to-depth ratio is dependent on the normal distribution of internal stress in beam.
(3) The shearing strength is affected by the span-to-depth ratio of the wooden beam. As the span-to-depth ratio is increased, it is observed generally that the shearing strength decreased.
(4) Table 2 illustrates the strength properties of HINOKI and RED LAUAN beams and comparison on an average (av.) and deviation (dev.) of the measured and calculated bending strength. The measured bending strength of beam specimens agrees resonably well with those computed, as a whole, falling in the range from 0.83 to 1.11. And Table 3 shows the distribution of the shearing stress to the modulus of bending rupture.