Preparation Process And Mechanical Properties Of Domestic Japanese Larch Cross-laminated Timber

Cross-laminated timber(CLT)is a prefabricated solid engineering wood products,and it is composed of orthogonally bonded layers of solid sawn lumber or structural composite lumber using adhesive,which have gained popularity in wood structure buildings in wall,roof,and floor applications.In particular,CLT is widely used to build high-rise wood structure buildings in Europe and North America,but the research on CLT is in the early stages in China,the lack of mechanical properties for CLT products limits its application in building structures.It is of great practical significance for application of CLT in the building structure,as well as to broaden the plantation timber and increase its added value,through research on the production process,mechanical properties and mechanical model of CLT fabricated with plantation.In this paper,it was to determine process parameters of CLT fabricated with Japanese larch(Larix kaempferi Carr.)including pressure,glue consumption,and adhesive.The bending,interlaminar shear,rolling shear and compressive properties of CLT were studied.The effect of the plate modulus,the direction of lay-up and the number of layers on the mechanical properties of CLT was studied.The finite element numerical model and theoretical calculation model were established.The main results of this research are summarized as follows:1.The experiment data of delamination and block shear strength for CLT were analyzed using range analysis,which indicated that the optimum process parameters were A2B3C2 including pressure(1.2 MPa),glue consumption(200 g/m2),and adhesive(PUR).2.The research on influence factors of mechanical properties for CLT(1)With the modulus of elasticity of top and bottom lumber increased from 10.33 GPa to16.21 GPa,the bending strength and modulus for CLT increased by 47.48% and 62.09%,respectively;there was no significant difference in the interlaminar shear modulus between146 MPa,interlaminar shear strength increased by 24.56%;there was no significant difference in rolling shear modulus between 138 MPa,rolling shear strength increased by 14.92%;the compressive strength and modulus increased by 34.48% and 72.45%,respectively.(2)With the thickness of timber decreased from 25 mm to 15 mm,the number of layers of CLT was same,the bending strength and modulus for CLT increased by 8.24% and 2.30%,respectively;there was no significant difference in the shear modulus,interlaminar shear strength increased by 24.41% and rolling shear strength increased by 37.93%;the compressive strength and modulus increased by 4.75% and4.85%,respectively.(3)With the number of layers increased from 3 to 5,the thickness of timber was same,the bending strength and modulus for CLT decreased by 20.94% and 14.82%,respectively;the interlaminar shear strength and modulus decreased by 26.26% and 3.92%,respectively;the compressive strength and modulus decreased by 17.76% and 9.36%,respectively.(4)Compared with the orthogonal CLT,the bending strength and modulus for inclined 45 degrees CLT increased 4.24% and 3.69%,respectively;the interlaminar shear strength and modulus increased by 44.64% and 24.94%,respectively;the rolling shear strength and modulus increased by 31.50% and 19.09%,respectively;and the compressive strength and modulus increased by 15.45% and 15.82%,respectively.(5)The fit linear model were selected to regress the mechanical properties of CLT.Relation models among mechanical properties were established.(6)The bending modulus for CLT had no significant difference with the width decreased.And with the span to depth ratio increased,the bending modulus for CLT increased.The bending modulus of nondestructive testing for CLT is lower 11.42% than that of static testing.3.CLT model was established using ABAQUS software.The relative error of the maximum failure load of bending,interlaminar shear and compression between the predicted value and the measured value was less than 10%.The relative error was small,the finite element model was correct,and the model cloud be used to predict the mechanical properties of 3,5,and 7layers L-CLT,M-CLT,and H-CLT.4.The effective bending stiffness,moment bending resistance and effective shear stiffness of CLT were predicted using “Mechanically Jointed Beams Theory(Gamma method)”,“Composite Theory(K method)”,“Simplified Design Method”,and “Shear Analogy Method”.The relative error between the predicted value and the measured value was about 10%.Theeffective bending stiffness and effective shear stiffness of 3,5,and 7 layers of CLT were calculated by shear analogy method.The simplified design method was used to predict the moment bending resistance of 3,5,and 7 layers of CLT.