Abstract:

The bending, tensile and compression properties of 596 pieces of Chinese Fir dimension lumbers with 45 mm×90 mm cross section on three visual grades, SS, No.1 and No.2, were investigated in this paper. The results showed: the mean values of modulus of elasticity (MOE), modulus of rupture (MOR), ultimate tensile strength (UTS) and ultimate compression strength (UCS) were shaping like "V" from grade SS, No.1 to No.2, and those test values of lumbers on grade No.1 were all similar or slightly lower than that of on grade No.2. The 5^th percentile value of those strength properties were observed to decrease from grade SS, No.1 to No.2, while there no significant change for MOE was observed among the visual grades. The values of MOR, UTS, and UCS had statistically significant differences on three grades at the 0.01 probability level. Moderately good correlation was observed between the mean values of MOE and the MOR, UTS, and UCS in the same MOE ranges, which can be quantified the relations of three main mechanical strengths when sample size was not big enough.

Key words: Chinese Fir, dimension lumber, visual grading, full-size specimen&rsquo, s mechanical properties