Effect of axial force-to-moment ratio on initial rotational stiffness of double-node system

Double-node system is a typical end-face connector for spatial structures. It is found that the initial rotational stiffness of this connection is affected by the axial force of the member. This study aims to investigate the effect of the axial force-to-moment ratio lambda on the initial rotational stiffness K0 of the double-node system. An analytical model composed of springs and a rigid plane is proposed according to the force transmission mechanism. The K0 lambda curve first exhibits linear, then inverse proportional, and finally linear again, corresponding to the three mechanical states. Next, the component stiffnesses are illustrated by parametric studies, which are related to the geometrical parameters of the connection. And the component stiffnesses are used to derive the constant coefficients of the overall stiffness in the K0-lambda formula through the component method. Finally, the process of determining the initial rotational stiffness is described, followed by some examples. Comparisons show that the proposed formulae are consistent with the numerical results, which are effective for predicting the initial rotational stiffness of the double-node system under different axial force-to-moment ratios.