In civil engineering structures constructed in cold snowy regions such as Hokkaido or Tohoku, repeated freezing and thawing of the wooden materials may occur in winter. To understand how the strength of wood changes because of these freeze-thaw cycles, we evaluated the bending strength of both untreated and preservative-treated Sugi (Cryptomeria japonica D. Don) timber under five regimes of freeze-thaw cycles, while varying moisture content.
Each cycle lasted 24 hours, and freeze-thaw regimes were composed of 0, 15, 45, 75, and 90 consecutive cycles. After each sample was subjected to a freeze-thaw regime, a bending test was carried out. There was almost no difference among the values of modulus of rupture or modulus of elasticity in samples subjected to different regimes. Moreover, as modulus of rupture and modulus of elasticity may increase after repeated freeze-thaw cycles, we concluded that the effect of the freeze-thaw cycles on the bending strength of Sugi timber is small.

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