11.THE EFFECT OF LOADING TIME ON THE BENDING STRENGTH AND STIFFNESS OF WOOD

Sugiyama Hideo

doi:10.3130/aijsaxxx.52.0_85

In this report are presented the results of a series of tests on strength and stiffness of SUGI (Cryptomeria) rubjected to rapis loading and long-time loading. The tests have been continued since 1949. In rapid loading tests, loads were applied by suddenly removing a support at one end of a catilevered beam with a weight connected thereto. Consequently, some beams failed (the time to failure was about 0.2sec) and some were vibrated without failing. In the latter cases the same loading procedures were repeated until they failed eventually. Long-time loading tests or "creep" tests were carried out under natural air condition and dead loads were sustained for 6 to 10 months at the free end of cantilvered specimen. The conclusions obtained are: (1) Modulus of rapture due to bending increases (decreases) as the time of loading decreases (increases) below (beyond) that under normal static loading. Within the range ofl oading time from 0.2 sec up to 10 months. The increasing (decreasing) rate of modulus of rapture is approximately 9% for a tenfold decrease (increase) of loading time. (2) The effect of long-time preloading on modulus of rapture under normal static loading is not disclosed. (3) When a specimen has been vibrated until it fails, the failure load gradually decreases as the number of repetition of vibration increases. (4) Modulus of elasticity under rapid loading is in general increased to some extent(less than 20%) than that under normal static loading. On the other hand, static modulus of elasticity for specimens subjected to long-time preloading are decreased, whereas those specimens show brittle behavior in their loaddeflection relationship, in other words, something like work-harnening effect is observed. (5) Deflection at maximum load is somewhat smaller under rapid loading than under normal static loading. (6) Specimen of cryptomeria subjected to bending fails under the load corresponding to about 60% of the normal static modulus of rapture after such load has been sustained for 6 to 10 months. (7) When a specimen is reloaded after the sustained load is completely removed, it shows increased modulus of elasticity corresponding to the amount and the time of sustained preloading.

11.THE EFFECT OF LOADING TIME ON THE BENDING STRENGTH AND STIFFNESS OF WOOD

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