Comparisons of Steel Joint Rigidity Classification Criteria and Assessment Methods Under Chinese， American， and European Design Standards

In the design of steel structures， the rigidity classification of joints in the calculation model is necessary before conducting global analysis and member design. Therefore， determining the rigidity classification of joints is a fundamental and critical task in steel structure design. Through a comparative analysis of the definitions， classification requirements， and judgment methods for the rigidity classification of steel joints under elastic design in China， the United States， and the European Union， it was found that the design standards of all three regions classify joint rigidity according to the mechanical characteristics of the connections， categorizing them into three types： rigid， semi-rigid， and pinned joints. The requirements of joint rotational stiffness in Chinese， American and European standards are defined by the moment-angle （M-φ） curve of the joint. The joint rigidity classification in Chinese standards is based only on the conceptual description of the M-φ curve， and neither the rotational stiffness of joints nor the rotational stiffness limit of joint rigidity classification can be defined quantitatively. Although the limit of rotational stiffness for the rigidity classification of beam-column joints is defined in American standards， there is no calculation method for the tangential stiffness of the joints. The calculation formula of rotational stiffness of common beam-column and column-base joints， as well as the requirements for the rotational stiffness limit in joint rigidity classification are given in EN standards. In terms of the detail requirements for joint rigidity classification， both American and European standards require that pinned joints must possess a certain rotational capacity， so the bolts and plates connected by end plates must meet flexibility and ductility requirements in detail， and ensure rotation capacity in the structure of the single-plate connection. Since rigid joint bear large bending moments， the flanges and webs of H-shaped steel columns often need to be strengthened， and the corresponding strengthening methods are provided in Chinese， American， and European standards. Therefore， both Chinese and American standards can only "qualitatively" determine joint rigidity classification through details. The European standards can "quantitatively" determine whether a joint is rigid， based on the calculation formula for the rotational stiffness of common joints and the rotational stiffness limit requirements for joint rigidity classification. Of course， for complex joins， it is still necessary to determine the M-φ curve of through tests or finite element analysis. In the design of steel joints， attention should be paid to the detailing requirements and factors influencing the determination of joint rigidity classification. In structural analysis， the influence of joint rigidity classification which simplifies the application of the calculation model must be considered.