Study On The Applicability Of North America Visual Grading Rules For Dimension Lumber Of Chinese Fir Plantation

In this paper, we studed on three main aspects which were the visual grading of dimensionlumbers of Chinese fir (Cunninghamia lanceolata) plantation, the relationship between knot,density, growth ring width and visual grades, and the mechanical properties of full-sizesamples and small clear wood samples and their relationship in order to evalue the quanlity ofdimension lumbers of Chinese fir more accurate, understand the relationship of the mechanicalproperties between full-size samples and small clear wood samples, verify the rationality ofvisual grading. And we hope those researches can be the basic plat for the futher study onstrength reduce defects and the effects of density of plantation and growth ring width on visualgrades, can provide data support for the study on the applicability of North America visualgrading rules for dimension lumber of Chinese fir plantation, and can afford the testingfoundation for establishing and developing of visual grading of dimension lumber of domesticspecies.During this study, we separated dimension lumbers according to NLGA, whose grade nameswere SS, No.1 and No.2 which equaled toⅠ_c,Ⅱ_c,Ⅲ_c in GB5005-2003. The MOR and MOEof Full-size samples were tested according to GB50329-2002, and consulted to ASTM D198,ASTM D4761 while the mechanical properties of small clear wood samples were tested byChina national standard. We chosed the typical producing areas for sample's trees collecting,and the quantity of the dimension lumbers for each area, visual grade and testing cell were notless than 30 pieces.The main results of this dissertain are as follows:(1) Knot degrades the dimension lumbers by the ratio of its area on cross section or by theequivalent diameter, and the effects of knot can be separate two main knid: edge knot andcenter knot; Wane by its length and thinness; Decay by the number of its areas, and the widthand depth of the area; Skips by the length and depth of its area; which the slope of graindegrades by the trend of the grain incline.(2)The results of visual grading showed: there were big differences among the quality ofAnhui, Hunan, Sichuan and Fujian's dimension lumbers, although knot was the maximumstrength reduce defect (MSRD), for it were various of the effects of knots on the quality oflumbers, while the MSRDs were different in four places; Decay and slope of grain wereexisting on the lumbers of each producing areas to different extents; the percentages of MSRDswere not the same while the ratio of each grades were different too: In the view of the ratio of SS grade, the quality of Fujian's dimension lumbers (49.08%) was better than Hunan's(41.62%), Anhui's (39.23%), and Sichuan's (28.32%); From the point of the total ratio ofSS, No.1, No.2, the quality of Anhui dimension lumbers was the best, following by Hunan,Sichuan and Fujian; And according the counterpoise of the ratio of SS, No.1 and No.2, thequality of Sichuan's was the best, following by Hunan, Anhui and Fujian; The result of thepercentage of SS was the hightest and that of No.2 was the second showed that we gained thesimilar conclusion with North America.(3)The average diameter of knots were increasing from grade SS to grade No.2 (SS was0.60in., No.1 was 1.08in., and No.2 was 1.40in.), which showed the visual grading of NorthAmerica was reasonable; From the view of strength only, we had better not use the averagediameter to estimate the MOR; The number of knots changed like "∧" from SS to No.2 (SSwith 3.57 knots, No.1 with 5.75); The number of knots was not determinant factor, but was adenoted factor for visual grading; Regression analysis results showed that the number of knotswas not the item for grading.(4)Each type knots had the same changes from SS to No.2 with the total analysis resultwhich were like "∧; The average number of each typle knots had a same orderliness: edgeknot＞cluster knot＞center knot＞three face knot＞knot group; From the ratios of eachtyple knots view, NLGA could separate the dimension lumbers of Chinese fir into tree gradespreferable; The grwothing conditions of trees and the method of swaing were the main reasonsfor this results.(5)The density of Anhui and Fujiand's dimension lumbers were increasing from SS toNo.2, while that of Sichuan were increasing and then decresing from SS to No.2, and thelowest was SS, while that of Hunan were decresing and then increasing; And the density ofSichuan's was the highest, while Fujian's was the lowest; Summarily, the density of Chinese firwere increasing from SS to No.2; It not had a good relationship between density and MOR offull-size samples.(6)The mean width of growth ring of Anhui, Hunan, Fujian's lumbers changed like shape "∧" from SS to No.2, while that of Sichuan's like shape "∨", which meaned the changesdifferent from producing areas; The mean width of growth ring of Fujian's were the hightest ofall, which SS was 5.65mm, No.1 was 6.11mm and No.2 was 5.58mm; It was a significantdifference among lumbers of the four places, which was due to juvenile wood.(7)The correlation analysis results showed that there was significant correlation betweenMOE and MOR of full-size samples, and the correlation coefficient was 0.695 at 0.05 significance level; And the regression equation was Y=0.0882X+6.2254, which couldpredict MOR value.(8)The MOR of fuul-size samples changed like shape "∨" from grade SS to grade No.2(SS was the highest with 49.09MPa, and No.1 was the lowest with 43.04MPa, while No.2 wasin the middle); The change of MOE from SS to No.2 was not obvious; Uneven repeat two-wayanalysis of variance results by SAS showed that the effect of visual grades on MOR of full-sizesamples was significant, whatever the effect of visual grades or the interaction of visual gradesand producing areas on MOR of full-size samples was not significant.(9)The UTS of Anhui, Hunan, Fujian and the total of four places' lumbers changed likeshape "∨" from SS to No.2, and SS was the highest while No.1 was the lowest; The changeof UTS of Sichuan's was decreasing from SS to No.2; Uneven repeat two-way analysis ofvariance results showed that the effects of visual grades and producing areas on UTS offull-size samples were significant, but the interaction of visual grades and producing areas wasnot significant.(10) Uneven repeat two-way analysis of variance results showed that the effects of visualgrades and producing areas on MOR of small clear wood samples were significant, but was notsignificant on UTS of that; The changes of both MOR and UTS of small clear wood sampleswere like "∨" from SS to No.2 and this phenomenon was not only due to growthingconditions of Chinese fir, but also related to the environment factors such climate and theprovenance difference.(11)The effect of visual grades on mechanical properties of small clear wood samples wassignificant, while that of producing areas was possible significant, so we should study more onthe effect of visual grades on mechanical properties of small clear wood samples; The rang ofMOR and UTS of full-size samples were 40-52MPa, 23-33MPa, which were about 53-77%and 34-39% of the value of small clear wood samples; The characters had more great effect onthe UTS of full-size samples compareing with that of small clear wood samples.(12)The lower-5% nonparametric tolerance limit with 75% confidence of small clearwood samples was 49.0MPa; The MOR characteristic values of SS, No.1 and No.2 were225.33MPa, 23.74MPa and 22.73MPa, while the strength ratios were 51.7% for SS, 48.4% forNo.1 and 46.4% for No.2; And the strength ratios for each visual grades were all a little lowerthan that of NLGA; Generally, NLGA was suit for evaluating the dimension lumbers ofChinese fir plantation.