2.2.3 Add Supports

Supports define how a structure connects to the ground by suppressing translations or rotations at nodes. In the “Support” component, an activated button appears black, indicating zero translation (T) in the direction of the global x-, y-, or z-axis, or zero rotation (R) about the corresponding global axis (or local axis if a plane is input). A node index or position can be used to specify the location of a support. To specify locally oriented support conditions, supply a plane as input.

Green arrows symbolize translational supports, while purple circles represent rotational supports (see Fig. 2.2.3.1).

Fig. 2.2.3.1: Supports specify how a structure interacts with the ground.

For static analysis, a structure must be supported to prevent it from moving freely. In three-dimensional space, a rigid body has six modes of movement or degrees of freedom (DOFs): three translations and three rotations (see Fig. 2.2.3.2). Therefore, a structural model requires at least six support conditions to be fixed. If a model or parts of it are moveable, the “Analyze” component will either refuse to calculate or return large displacements. If this issue arises, connect your model to the “Eigen Modes” component to detect the rigid body movements causing the problem.

Fig. 2.2.3.2: A body in space has six degrees of freedom (DOFs).

Supports can only be defined at structure nodes. If a support position is not set on a node, the “Assemble Model” component will issue an error. The error message will contain the coordinates of the support that does not attach to the model. To get an overview of the faulty model, deactivate the “Support” component and use the “ModelView” component to visually inspect the model.