Relations between Mechanical Properties of Visual Stress Graded Dimension Lumbers of Chinese Fir

摘要

In this paper, the modulus of elasticity (MOE), modulus of rupture (MOR), ultimate tensile strength (UTS) and ultimate compression strength (UCS) of visually graded full-size 2-inch-thick dimension lumber specimens of Chinese fir were studied in order to estimate the correlation between these properties. A sound understanding of the relation of mechanical properties within visual grades is important in establishing design properties that optimize the utilization of dimension lumbersproduced from Chinese fir. The cross section size of the samples was 45mm×90mm, and the totalnumber of pieces tested was 596. The results show: Chinese fir dimension lumbers can be separated into three grades, typically referred to in North America visual lumber grade rules as Select Structural (SS), No.1 and No.2. The mean values of MOE, MOR, UTS, and UCS didn't change uniformly from the SS grade to the No.2 grade. The No.1 grade was found to have similar or slightly lower test values than the No.2 grade. This was attributed to how the pieces were dropped from the No.1 grade to the No.2 grade because of non-strength reducing characteristics such as skip and wane. Generally, the 5th percentile value the strength properties were observed to decrease from the SS grade SS to the No.2, which no significant change in MOE was observed between the grades. The values of MOR, UTS, and UCS each had statistically significant differences among, between grades at the 0.01 probability level. Moderately good correlation was observed between the MOE and the MOR, UTS, and UCS.