The connection between the leg members and diagonal members of the urban transmission line tower is mostly in the form of single-limb connection. This paper puts forward a new connection form of pipe double-limb double-plate connection joint, which is based on the model of key joints in an urban narrow base tower structure. The traditional pipe single-limb single-plate and new pipe double-limb double-plate joint are analyzed and studied from three aspects of theory, numerical simulation and experimental study. Through finite element analysis, it is obtained that the section stress of angle steel under eccentric load is 2.05 times of that under axial load, which is basically consistent with the 2.5 times of the theoretical calculation. This shows that the stress of the angle steel in the pipe double-limb double-plate joint is greatly reduced as the axial stress component, which can ensure the safety of the angle steel. Based on the theoretical analysis of the tensile force of two kinds of joints, through the test research and corresponding numerical simulation of pipe single-limb single-plate and pipe double-limb double-plate joints, under the same load, compared with pipe single-limb single-plate joints, the pipe double-limb double-plate joints designed in this paper can greatly reduce the stress of connection plates and members, and compared with the existing joint forms, the bending stress of joint plates can be reduced by about four times, which greatly improves the bearing capacity of the joint. The research on the pipe double-limb double-plate connection joint will provide the basis for the design of new connection joints of narrow base towers in urban areas.

Transmission tower connection joint is an important connection component of the tower leg member and diagonal member. Its axial stiffness directly affects the stable bearing capacity of a transmission tower. The axial stiffness of the joint is mainly related to the connection form of joint. This paper takes the double-limb double-plate connection joint as the research object. Through the comparative study with the single-limb single-plate connection joint, the influence law of single-limb single-plate and double-limb double-plate joint on stable bearing capacity of quadrilateral transmission tower is studied from three aspects of model test, theoretical analysis and numerical simulation. Through the scale model test, it is found that the elastic stiffness of the double-limb double-plate joint is 3.12 times that of the single-limb single-plate joint, which can increase the bearing capacity of the joint by 26.1%. Through the energy method, the theoretical calculation expression of the stable bearing capacity of the quadrilateral tower considering the influence of the axial stiffness of the joint is derived. Compared with the effect of the single-limb single-plate connection joint, the double-limb double-plate joint can improve the stable bearing capacity of the quadrilateral tower by 15.6%. Considering the influence of geometric nonlinearity of tower and connecting joint, it is found that the double-limb double-plate connecting joint can improve the nonlinear stability bearing capacity of a transmission tower by 14.9%. The results show that the double-limb double-plate connection joint can not only improve the bearing capacity of the joint, but also greatly improve the stable bearing capacity of the tower. The research results can provide reference for the engineering application and design of double-limb double-plate connection joints.

The axial stiffness of the connection joints in a transmission tower will affect the stability bearing capacity of the tower. The axial stiffness of different forms of connection joints has different effects on the stability bearing capacities of triangular and quadrilateral lattice towers. This paper takes triangular and quadrilateral lattice towers as the comparative research objects and considers the influence of the stiffness of the single-limb, single-plate joint (SLSPJ) and double-limb, double-plate joint (DLDPJ) of the tower. Under vertical load, the vertical stability bearing capacities of triangular and quadrilateral transmission towers are studied from hte three aspects of theoretical analysis, numerical simulation and test result analysis. The influence rules of the SLSPJ and DLDPJ on the vertical stability bearing capacities of triangular and quadrilateral transmission towers are clarified. Through the energy method, considering the influence of the axial stiffness of connection joints, the calculation expressions of the vertical stability bearing capacities of triangular and quadrilateral lattice towers are derived. Through quantitative analysis, it is found that the axial stiffness of the connection joints has a more significant influence on the vertical stability bearing capacities of triangular lattice towers. The finite element models of the triangular and quadrilateral lattice towers including the SLSPJ and DLDPJ are further established. Through nonlinear finite element analysis, it is found that the DLDPJ can improve the vertical stability bearing capacity of the triangular lattice tower by 22.7% and the quadrilateral lattice tower by 14.9%. Through theoretical calculation, the expressions of the vertical stability bearing capacities of the triangular and quadrilateral lattice towers including the SLSPJ and DLDPJ are obtained. Combined with the test results of the SLSPJ and DLDPJ, it is found that the DLDPJ can improve the vertical stability bearing capacity of the triangular lattice tower by 23.4% and the quadrilateral lattice tower by 15.6%. The research results show that the DLDPJ can improve the vertical stability bearing capacities of triangular and quadrilateral lattice towers. The improvement effect of the vertical stability bearing capacity of the triangular lattice tower is 1.50∼1.52 times that of the quadrilateral lattice tower. The research results can provide a reference for the engineering popularization, application, and design of the DLDPJ in transmission towers.

The grain shape and orientation distribution of metal sheets at mesoscales are usually irregular, which has an impact on the elastic properties of metal materials. A grain shape function (GSF) is constructed to represent the shape of grains. The expansion coefficient of GSF on the basis of the Wigner D function is called the shape coefficient. In this paper, we study the influence of average grain shape on the elastic constitutive relation of orthogonal polycrystalline materials, and obtain a new expression of the elastic constitutive relation of polycrystalline materials containing grain shape effects. The seven string method is proposed to fit the shape of irregular grains. Experiments show that the GSF can better describe the shape of irregular grains. Using the microscopic images of the grains, we carried out the experimental measurement of micro and macrostrain at grain scale. The experimental results show that the grain shape parameter (slenderness ratio) is consistent with the theoretical results of the material macroscopic mechanical properties.

The number of distinct components of a high-order material/physical tensor might be remarkably reduced if it has certain symmetry types due to the crystal structure of materials. An nth-order tensor could be decomposed into a direct sum of deviators where the order is not higher than n, then the symmetry classification of even-type deviators is the basis of the symmetry problem for arbitrary even-order physical tensors. Clearly, an nth-order deviator can be expressed as the traceless symmetric part of tensor product of n unit vectors multiplied by a positive scalar from Maxwell’s multipole representation. The set of these unit vectors shows the multipole structure of the deviator. Based on two steps of exclusion, the symmetry classifications of all even-type deviators are obtained by analyzing the geometric symmetry of the unit vector sets, and the general results are provided. Moreover, corresponding to each symmetry type of the even-type deviators up to sixth-order, the specific multipole structure of the unit vector set is given. This could help to identify the symmetry types of an unknown physical tensor and possible back-calculation of the involved physical coefficients.