A Study On Finger Joint Technique For Laminations In The Structural Larch Glulam

Larix gmelinii is an important commercial forest timber resource,and it’s a kind of idealmaterial for wood structural timber, which owns fast growth, high strength, decay resistancecharacteristics and so on．Glued laminated timber(Glulam) develop so fast and becoming themain direction of wood structural building．As the primary member of glulam, finger-jointlamina can improve wood utilization rate through realize short material with long and inferiormaterial with excellent, So the lamina is the key technology of structural glulam research．In this paper, Dahurian larch was studied, and the cross-section dimension of sampleswere two types：40mm×65mm,40mm×90mm．Through carried out the study of glulam laminafinger joint process, mechanical properties test and mechanical classification, we obtained theoptimum finger profile and process．Analysised the variation of mechanical property and it’sinfluencing factor．Graded the lamina based on JAS1152standard, evaluated whether themechanical property up the standard requirement．Provided the data support and technologyconsult for optimized domestic larch resource as the structural timber, promoted the exploitionand utilization of finger joint product made by commercial forest timber in our country, in thesame time, offered the theory consult of study in lamina finger joint used other domestic treespecies．The main results of this paper were summarized as follows：(1)The load-displacement curve could be divided into three types on the base of differentfitness ratio, two line continuance, single line continuance and two line discontinuance．singleline continuance was the optimal curve type, and its corresponding fitness ratio was the best．Itcould be concluded that the optimum fitness ratio of14mm and19mm finger profile was0.1mm, and the25mm and28mm was0.2mm．The optimum endpress of14mm finger profilewas about12.5MPa with12.7mm finger length, the optimum endpress of19mm finger profilewas about11.5MPa with19mm finger length, the optimum endpress of25mm finger profile was about11MPa with25mm finger length, the optimum endpress of28mm finger profile wasabout10MPa with27.5mm finger length．The endpress value gained in the test was in theendpress scope of structural finger-joint timber and fit the rule of the standard．(2) The change of the finger length had significant influence to the MOR of larchstructural finger-joint lamina, but MOE would not appear significant change along with thechange of finger length．The MOR of12.7mm sample distributed concentric, and thecoefficient of variation lesser；The coefficient of correlation of MOE and MOR of12.7mmsample was the highest in three finger profiles；The12.7mm finger-joint sample would producemore higher mechanical grade lamina．Finally, analysis by synthesis,12.7mm sample weremore in favor of the structural glulam lamina that with high mechanical property, well strengthstability and high security coefficient．Its definite finger profiles were12.7mm of fingerlength,4.0mm of pitch,0.8mm of tip thickness,0.1mm of fitness ratio,1/10.8of slope．(3) The influence of the finger joint in this test to the dynamic MOE were very small, itdemonstrated that the process and finger profiles of this test were very good．The parallel graincompression MOE of lamina decreased significant after finger joint, but the bending MOEalmost increased after finger joint and the difference was not significant before and afterjoint．The MOE had certain correlation with parallel grain UCS of larch finger-joint lamina,had better correlation with MOR, had good correlation with parallel grain UTS．The MOR offinger-jointed lamina shew the significant dimensional effect like the dimension timber．(4) The every grade finger-joint lamina used finger profiles and process that studied in thispaper were able to reach the strength requirement after carried static bending MOE gradingthrough JAS1152standard．The number of upper L110grade finger-jointed lamina occupyedthe41%of total lamina．It verified that the glulam lamina finger joint technology studied bythis paper was very good and adapt well with the Larix gmelinii．...