A joint stiffness classification method for six-bar tetrahedral latticed shells considering the effect of axial force-to-moment ratio

The six-bar tetrahedral unit exhibits excellent adaptability to complex free-form spatial structures. The rotational stiffness K of its assembled joint is sensitive to the ratio of the applied axial force to moment λ . For the accuracy of the global structural analysis, a comprehensive study of this behavior is essential for the development of a joint stiffness classification method. Therefore, the influences of web member forces and inclination angle of members on the behavior were investigated, and a simplified finite element model of the six-bar tetrahedral unit joint was presented for the subsequent analysis. Then, a parametric analysis was conducted to investigate the influence of the number of bolts, end plate thickness, and bolt size on the K - λ behavior. An upper limit of K was developed to define the State I of the K - λ curve, where the joint exhibits behavior comparable to a fully rigid connection. Next, an ANSYS-MATLAB co-simulation method was proposed and compared with the traditional semi-refined model and refined solid element model. The results confirm the necessity of incorporating the K - λ behavior in the global analysis, which can be accomplished by the proposed co-simulation method. Finally, the stability of six-bar tetrahedral latticed shells with various structural types was investigated to develop the joint stiffness classification method. Different structural forms yield different distributions of joint mechanical states, which significantly affect the reduction of critical loads. The joint in the double curvature shallow latticed shells can be idealized as a rigid connection in the global analysis, whereas in cylindrical and spherical latticed shells, it needs to satisfy certain configuration requirements.