Non-destructive Testing On Properties Of Fast-growing Wood Laminated Lumbers And Its Finger-jointed Lumbers Of Structural Glulam

Wood-based buildings are becoming increasingly popular as their reputation of environmental, renewable materials. Currently, with the shrinkage of natural forestry resources, there are fast growing, lower quality wood resources instead. Hence, research and development of Structural Glued Laminated Timber (Glulam) made of fast growing wood has a meaningful theoretical sense and economic value, not only complementing the shortage of big diameter, high quality wood, but promoting the development of wood-based structure industry.As for Structural Glulam, it is extremely significant to ascertain the grade of its laminar to raise the strength and rigidity of the products. In terms of modulus of elasticity (MOE) of wood is the main referenced standard, this thesis carry out comprehensive research on the dynamic modulus of elasticity of fast growing Structural Glulam's materials(Cunninghamia lanceolata lumber, Pinus massoniana lumber and finger-jointed Cunninghamia lanceolata lumber) by ultrasonic non-destructive testing method and fast flourier transformation (FFT) spectrum analyzer. The major innovational points of this thesis are that viewing a great number of Cunninghamia lanceolata lumbers as specimens, resonance frequency is acquired only by FFT spectrum analyzer program in a computer and the correlation between dynamic MOE and static bending MOE is in great agreement.The core conclusions are as follows:(1) The correlation between the dynamic MOE of Cunninghamia lanceo- lata lumber with three depths by FFT spectrum analyzer and that by ultrasonic is extremely significant, so does the relation between dynamic modulus of elasticity and static bending MOE.(2) The velocity of ultrasonic through specimen accelerates with the in- crease of static bending MOE and descends as the depths of specimens become thick. As far as the same depth of Cunninghamia lanceolata lumber, the change of value of resonance frequency varies identical with static bending MOE. To specimens of different dimensions, its resonance frequency demonstrates a trend of decreasing with the growing of the depths.(3) The method of FFT spectrum analyzer is superior to that of ultrasonic. First of all, the former do not need any medium such as butter. Meanwhile, as its simple, rapid characteristic and the acquirement of resonance frequency not affected by tap material, tap positions, hold positions and supportive conditions, this method is more easily to carry out in the product line. More importantly, the correlation coefficient between dynamic MOE and static bending MOE illustrates that the results tested by FFT are more credible. Most important of all, this method presents a lower cost because it do not need non-destructive equipment.(4) The correlation coefficient of 0.965 for 529 Cunninghamia lanceola- ta lumber under moisture content of 15 percent illustrates its near perfect agreement between ESF and ELV is a bit little better than that of Pinus massoniana Lamb. lumber. What is more, the correlation coefficient of 0.960 for 529 Cunninghamia lanceolata lumbers together with 211 Pinus massoniana Lamb. lumbers indicates that the method of FFT spectrum analyzer has a universal meaningful sense, affected slightly by the different species of wood.(5) Whether Cunninghamia lanceolata lumber or Pinus massoniana Lamb. lumber, the agreements between their density and static MOE are very low, with no significant correlation of the former and low relation degree of the latter, its coefficient of 0.313. However, there is a trend exsiting in these two species that static bending modulus of elasticity rises as the value of density goes up.(6) With the increasement of the number of knots, density of Cunningha- mia lanceolata lumber increases while the values of MOE decreases. On the other hand, density increases and the values of MOE decreases with the increasement of heartwood ratio. Consequently, the correlation agreement between MOE and density is not very good.(7) The values of resonance frequency and dynamic MOE of Cunningha- mia lanceolata lumber both ascend with its moisture getting down. The results show that the change of moisture content has no significant effect on the correlation between ESF and ELV, therefore, when the moisture content ranges from 10 percent to 20 percent, its static bending MOE can be predicted by the correlation equation under moisture content of 15 percent.(8) It is considered that MOR is related significantly to dynamic MOE, showing a coefficient of 0.623. Therefore, the regression equation is adopted for predicting the laminar MOR.(9) The distributions of knot data in each grade of Cunninghamia lanceo- lata lumber, divided according to dynamic MOE, show there are little difference between each grade, so does the result gained by single variance analysis.(10) It is concluded that ESF is correlated significantly to ELV of Cunning- hamia lanceolata lumber after finger-jointed, with coefficient of 0.965, not lower than that before finger-jointed. The results also show that finger jointing has no significant effect on the values of ESF, ELV, as well as the correlation between ESF and ELV.