Finite-Element Model for Thin-Walled Space Frame Flexible Connection Behavior

A finite-element formulation for modeling flexible connection behavior in space frames composed of thin-walled members is presented. The finite-element model is based on a distributed linear spring representation over the physical contact area of the connection that is capable of representing translational, rotational, and warping deformations of the connection. Second-order geometric and nonlinear moment-rotation response of the connection is considered. An updated Lagrangian formulation is used to model second-order geometric nonlinear effects. A Ramberg-Osgood representation is used to model the nonlinear moment-rotation connection behavior. Details for transforming the resulting stiffness equations for connection-to-member eccentricities are included. Results for a cubic, portal space frame composed of I-section and C-section members are presented to demonstrate the versatility of the developed element.