Study On Calcalation Method Of Equivalent Compression Stiffness Of Bolted Joints

Bolt connection is a detachable fixed connection, except for many advantages, i.e., reliable connection, convenient assembly, variety of types and conducive to maintenance, which also has good mechanical performance and seismic capacity. Bolt connection is widely used in engineering filed, and its service environment is complex and changeable. If safety problem not fully considered and strength or function does not reach the related requirements in the bolt design and verification process, there will be serious security risks. By comparison of bolt compute methods and related compute standards, the thesis finds that compute of bolt connection contains two aspects of requirement, strength and function. Which mainly focus on several points, i.e., assembly stress, operating stress, fatigue alternating stress, connected surface pressure, prevent skidding verification, shear force, tightening torque, and etc. The most important thing for compute of bolt connection is the calculation of the external load distribution ratio, which mainly lies in the compute of equivalent stiffness of bolt and connected parts. Its degree of accuracy directly affects the compute results of the bolt connection.The disc-like connected parts were taken as the subject of the study and the simplified shape of the equivalent compression deformable bodies with different shapes and sizes (such as:the cone, the column and the column) were analyzed. Meanwhile, based on the compressive stress uniform distribution and non-uniform distribution of transverse section, which is perpendicular to the bolt axis, equivalent compression stiffness calculation formula of hollow cone and the hollow cylinder was derived. Afterwards, a large number of different sizes for the connecting pieces of M12 are selected, and the equivalent compression deformation of the connecting piece included almost every shapes that may arise in this size. The finite-element calculation of bolt connection with various size leads to the acquisitions of the simulation results for axial compression stiffness. After that, comparison of simulation results and theoretical formula calculations were taken. Finally, based on the VB software, the compute program is compiled, by entering parameters of bolt, connected parts, loads and etc. overall verification for bolt connection can be carried out.The analysis shows that, if clamping thickness of connected parts is small, when the equivalent compression deformation of the connecting parts is simplified as a hollow cone, the errors between the results of theoretical compute based on compressive stress non-uniform distribution and the calculation of finite-element is less than 5%, which also can be over 10% when clamping thickness is large. The calculation based on compressive stress of non-uniform distribution has a difference between that of uniform distribution, and the difference can reach 5% when the equivalent compression body of connected piece is simplified as a hollow cone+hollow cylinder. Moreover, at this case, the calculation based on the non-uniformly distributional compressive stress is closer to the compute of finite-element compared with that based on uniformly distributional compressive stress. Both of calculations based on the non-uniformly distributional compressive stress and uniformly distributional compressive stress are very close to the compute of finite-element, no matter what material it is, if the connected piece was simplified as hollow cylinder.