Study On The Technology And Structural Performance Of Chinese Fir Glued-laminated Beams

Wood is an ancient construction material. In the 1950's and 1960's, a vast number of timber structures were built because of natural forestry resources, which lead to the shrinkage of timber structure. Wood structure suspended for 20 years, and disappeared gradually. Wood-based buildings are becoming increasingly popular as their reputation of environmental, renewable materials. With the economy developing, there are a variety of demands for building structure. North America and some other countries have exported light wood frame construction to China. Therefore, wood-based structure has been revived.There are large areas of fast growing plantation in China. The developing of wood science and technology makes it applicable to civil engineering. Glued-laminated timber(glulam), made of fasting growing plantation, make inferior timbers a feasible candidate for wood structures, improve timber utilization and strongly promote the development of wood-based constructions. Selecting Chinese fir(Cunninghamia lanceolata) as experiment material, in the base of analyzing home and abroad research results, with the combination of experiment and theoretical analysis, the research focused on the technology and structural performance of Chinese fir glulam laminated beams.The research methods refer to JAS about structural glulam, ASTM D 4761 and D198, and fast flourier transformation(FFT) spectrum analyzer. The main content and results included in the following items.1 With the study on the finger-jointing technology of Chinese fir lumbers, the results are as follows: The correlation coefficient of o.965 for Chinese fir lumbers illustrates its near perfect agreement between static modulus of elasticity(MOE) and dynamic MOE. According to MOE, classify the lumbers with 4 grades. The gluability with bi-component adhesive is much better than monocomponent adhesive. The static MOE is correlated significantly to dynamic MOE of Chinese fir lumbers after finger-jointed, with coefficient of 0.960, which indicates that the method of fast flourier transformation(FFT) spectrum analyzer has a universal meaningful sense.2 Study on processing variables of Chinese Fir Glulam, the results indicated that optimum technological parameters are pressure at 0.8MPa, the adhesive spread of 250g·m-2and the additive taking up 10% of the adhesive. The gluability with bi-component adhesive is better than melamine-phenol-formaldehyde co-condensated resin(MPF), but the boiling water resistance is lower than MPF. Treatment with CCA does not decrease the gluability.3 Based on the physical properties of Chinese fir, presented the producing technology of Chinese fir Glulam. According to study on the MOE of glulam beams, the conclusions are: (1) the effects of load application rate and span on static MOE are not significant when a=0.05.Elasticity aftereffect distortion is a factor of MOE variance with many tests. (2) the correlation coefficient above 0.92 illustrates its near perfect agreement among static MOE,dynamic MOE and model predicting MOE, Which indicates that it is feasible to forecast the glulam MOE with FFT spectrum analyzer and predicting model.(3) there are significant correlations among Chinese fir lumbers MOE,finger-jointed laminates MOE and glulam beams MOE, with the correlation coefficient above 0.93, which verifies the feasibility of predicting glulam MOE with lumbers MOE and laminates MOE.4 By means of modulus of rupture(MOR) test and ultimate flexural loading calculation of Chinese fir glulam beams, the study reveals that: (1) the form of failure is tension brittle fracture. Most beams are failure resulting from finger-joint. To avoid finger-joint and knot in pure bending part is the key of promoting glulam performance. Bamboo slice facing can reduce the risk of rupture. (2) MOR of glulam, with the minimum 23.75MPa and maximum 41.55MPa, corresponds to timber, and could meet the requirements for construction. Lamination's layers, configuration scheme, and bamboo slice facing are the effecting factors of ultimate flexural loading. CCA treatment does not decrease the strength of beams. (3)Based on experimental results and regression analysis of Chinese fir glulam, there is significant correlation between MOR and MOE, the correlation coefficient with dynamic MOE and static MOE 0.85 and 0.87 respectively. Hence, MOR can forecast with MOE. (4)On the premise of assumptions of plane cross-section,stress distribution,neutral layer,MOE and thickness of glue layer, this paper derives the simple formula of ultimate flexural loading of Chinese fir beams.