ANALYSIS OF THE BUCKLING STRESS OF AN INTERMEDIATE WOODEN COLUMN BY THE TANGENT MODULUS THEORY

The buckling stress for an intermediate wooden column was predicted based on the tangent modulus theory. Rectangular bars of Sitka spruce (Picea sitchensis Carr.) with various slenderness ratios were used for the specimen. Strain gages were bonded on opposite sides of LR (longitudinal-radial) planes which were wider than the LT (longitudinal-tangential) planes, and a compressive load was applied on the specimen supported with pin ends. The buckling stress was calculated from the load at the occurrence of strain reversal. The relationship between the buckling stress and the slenderness ratio was predicted by the tangent modulus theory, and was compared with the experimental results. Additionally, we thought that the shearing force would have some effect on the buckling stress, and hence, we examined the effect of the shearing force on the buckling stress. The rusults are summarized as follows: ( 1) The value of buckling stress predicted by the tangent modulus theory was influenced by the stress-strain equation used for giving the tangent modulus. The n-power function had drawbacks in predicting the buckling stress. On the contrary, the logarithmic function was suitable for the prediction. (2) The effect of shearing force was not very large in predicting the buckling stress of the intermediate column.