| Cross laminated timber(CLT)is a kind of structural composites,which is made by gluing three or more cross-ply specification-wood layers together.Compared with other engineered wood products,CLT is an excellent renewable building material with the advantages of high dimensional stability,high bearing capacity,good fire resistance and seismic performance.Because of its unique structure and excellent mechanical properties,CLT is suitable for structural members such as beams and walls.However,due to the low shear strength of its transverse layer,when CLT is subjected to out-of-plane bending,the transverse layer becomes the weak shear layer,resulting in the rolling shear failure of the structure.The rolling shear failure of CLT will significantly weaken the structural stiffness and reduce the bearing capacity of the structure.Therefore,the rolling shear problem has always been one of the hot issues in CLT structure research.Based on this,the bending and rolling shear properties of CLT flexural members are experimentally studied and analyzed in this paper.The main research work and results are as follows:(1)Taking three layers and five layers CLT plates as research objects,the bending tests of CLT plates were carried out,and the applicability of mechanical connecting beam theory,composite laminate theory,shear analogy method and simplified method in China’s wood structure design standard to the bending stiffness of CLT plates were compared.The results show that the plane section assumption is basically valid in the elastic stage of CLT bending deformation;The prediction results of the above four calculation methods are conservative,and the prediction of shear analogy method is more accurate.(2)According to different layers and tree species,the bending shear test of CLT plate were carried out.The results show that the shear failure process of CLT can be divided into two stages:linear loading stage and crack extension / propagation stage;The number of layers / total thickness of CLT plate has no significant effect on its shear capacity.Comparing the rolling shear properties of CLT plates made of Canadian spruce-pine-fir(SPF)and European spruce shows that,the latter is better than the former.(3)The finite element models of CLT plate bending and bending shear were established by ABAQUS software.The finite element model of CLT bending member can reasonably predict its bending performance;while the finite element model of CLT plate bending shear member underestimates its shear capacity due to the complexity of rolling shear mechanism. |
