Study On Process For Glued Laminated Timber Of Dahuria N Larch And Its Mechanical Properties

There is a vigorous development of wood construction in in China, the rapid devel opment of engineering wood is required. Glued laminated timber(Glulam) is one of th e most important one of engineering wood and it is urgent to research the glulam mad e from domestic species. Larch timber is an ideal structural timber with large forest sto cks, good durability and so on in China. Larch is used in this study, and some researc h have been done, including larch log grading, laminations machine stress rating, the e valuation of bonding strength, the mechanical property evaluation of larch glulam and s o on. The purpose of this paper is to intensively study the key technology of processi ng technology of larch glulam, so as to accelerate the development and utilization of g lulam products timber in China. The main results of this paper are as follows:(1)The log grades measured by longitudinal resonance methods(FFT) range from Ef90 to Ef130, the green laminations range from ME11 to ME14, and the dry laminations range from ME12 to ME18. The relationship between dynamic MOE of logs and mean dynamic MOE of laminations is more than 0.7.(2)According to mechanical stress rating(MSR) method, the laminations are separated into grades of ME11, ME12, ME14 and ME16, which account for 10.38%, 42.45%, 31.13% and 12.26% respectively. Grades ME14 and ME12 ae choosed to conduct tensile test. For the laminations of grade ME14, the average value of tensile strength and 5% characteristic value are 40.07 MPa and 27.61 MPa respectively, and they can achieve the values stipulated by GB/T50708-2012 ‘techanical code of glued laminated timber structures’ and GB/T26899-2011 ‘Structural glued laminated timber’. For grade ME12, the average value of tensile strength can satisfy values stipulated by the standard value, while 5% characteristic value is lower than the standard value.(3) We have tested the bonding strength of finger jointed laminations according by ASTM D4688 ‘Standard test method for evaluating structural adhesives for finger jointing lumber’. The average value of tensile strength of water-based isocyanate adhesive is 70.13 MPa under dry test, 21.50 MPa under cold water vacuum-pressure soak test, 18.74 MPa under cyclic boil test. While the values of one-component polyurethane adhesive under the three conditions are 55.36 MPa, 25.94 MPa and 23.08 MPa respectively. In addition, the optimum lamination pressure are 1.0~1.2MPa both for aqueous vinyl polymer solution-isocyanate adhesive and one-component polyurethane adhesive.(4) For the different grades of glulam in this experiment, we have measured the static MOE of glulam by local and globle modulus of elasticity in bending, the local MOE is 5.20~7.66% higher than the globle MOE. In this experiment, the global MOE of grades TCT30, TCT27 and TCT24 is 14.7 GPa, 13.14 GPa and 11.80 GPa. And the MOR is 53.25 MPa, 48.67 MPa and 32.16 MPa. Their average bending modulus of elasticity and bending strength can satisfy the mean values and characteristic values stipulated by GB/T50708-2012 ‘technical code of glued laminated timber structures’ and GB/T26899-2011 ‘Structural glued laminated timber’.