| In recent years,with the rapid development of construction industry in China,the architectural structure is becoming more and more diversified.As the National key research and development plan key special projects "Green Building and Building Industrialization" progresses,the research and engineering application of wood structure architecture have been greatly promoted.Modern wooden structures have been widely concerned at home and abroad because of its advantages of environmental protection and energy saving.Meanwhile,a variety of engineered wood products have also been put into practice,such as Cross-laminated Timber(CLT),Glulam,Laminated Veneer Lumber(LVL),Parallel Strand Lumber(PSL),etc.The excellant mechanical properties of these products greatly expand the application range of wood structure and strongly promote the development and application of modern large-span wood structure and high-rise wood structure.Cross-laminated timber(CLT)is one of the modern wood products.Due to the orthogonal laminates,CLT is often used in the construction of floors or walls.However,the design of in-plane connections in CLT floors and walls is one of the key points which can have great effect on the mechanical properties when using these products.At present,most of the researches on CLT floor in-plane connections are focused on the shear and seismic performance but few attention is paid to the flexural performance.Besides,there is no clear theoretical formula for the design of in-plane connections in standards such as CLT handbook,etc.The design of these connections is mainly based on engineering practice.Therefore,in this paper,the commonly used half-lapped joints are selected to carry out relevant experiments and theoretical research to study their flexural behavior.In this dissertation,the half-lapped joints in CLT floor was taken as the research object.The material performance tests,the flexural behavior tests of half-lapped joints along the weak axis and the flexural behavior tests of half-lapped joints along the strong axis have been carried out successively.The finite element simulation and theoretical analysis were carried out on the basis of experiments.The main research contents are divided into the following parts:(1)The research status of domestic and foreign scholars and research institutions on CLT floors and connections was summarized,including the flexural performance of CLT floor,the tensile strength and shear strength of self-tapping screws in CLT specimens,and the engineering application background of CLT inplane connections,etc.(2)The constitutive relation model of wood at room temperature was summarized and the definition method of the constitutive relation of wood in ABAQUS was introduced based on the user material subroutine VUMAT developed by our research group.Besides,the material performance tests of wood and self-tapping screws were carried out which can provide the foundation for the following numerical simulation and theoretical analysis.(3)The flexural behavior tests of 6 groups of specimens(a total of 18 specimens)were carried out and two situations were considered,including bending along the weak axis and bending along the strong axis.Among all the specimens,the flexural behavior tests of half-lapped joints along the weak axis contained 3groups of specimens(3 specimens each group)and the effects of the overlap length and screw spacing(number)on the flexural behavior were studied.Similarly,the flexural behavior tests of half-lapped joints along the strong axis also contained 3 groups of specimens(3 specimens each group)and the effects of screw diameter and screw spacing(number)on the flexural behavior were studied.(4)The finite element analysis was carried out with the half-lapped joints in CLT floors and parameter analysis was also studied on the flexural behavior of half-lapped joints bending along the weak axis and the strong axis respectively.The overlap length,screw diameter and screw spacing(number)were taken as the parameters for both half-lapped joints bending along the weak axis and the strong axis.(5)Based on the experimental and finite element analysis conclusions,and the relevant research results at home and abroad,a simplified method for calculating the ultimate bearing capacity of half-lapped joints bending along the weak axis was presented which was based on the assumption of rigid body model.In addition,a simplified method for calculating the shear connector in half-lapped joints bending along the strong axis was also presented which was based on the assumption of composite floor,in order to propose suggestions for engineering application. |
