Working with Supports

Dr. Frame2D includes the following types of supports: fixed supports; pinned supports; translational (multi- and unidirectional) and rotational springs; internal hinges; and line and plane roller supports. Examples of each are shown in the rather artificial example below:

In general, you can create supports by clicking at the desired location with the appropriate tool. You can also area drag a set of joints/nodes while holding down the alt/option key to install multiple supports at a time. This is discussed further in the Shear Wall documentation.
Supports can be removed by selecting them and pressing the delete or backspace key.

Change support type quickly by clicking on an existing support with a different type of support tool. For example, to change an existing Fixed Support to a Pinned Support click on the Fixed Support with the Pin Support Tool.

Supports can be relocated by dragging or, for in-span supports, by using the left/right cursor (arrow) keys. Relocating joint supports will also relocate the joint which has the side effect of modifying any attached members.
Rotational springs can be combined with pin supports to create conditions of partial fixity.
Support settlement can be modeled by control-dragging the desired support. The cursor keys can also be used: the up/down cursor keys will impose displacements to member supports and the left/right and up/down keys will impose displacements to joint supports. The control key will decrease the effect of each key press and the shift key will increase the effect of each key press. Pressing the 'zero' key while the support is selected will zero the imposed displacement.
Support orientation can be modified by holding down the control and shift keys together while dragging:

Supports can exist independently of other parts of a structure:

By choosing the Options>Joints & Supports>Show Support Reactions command (or pressing the '8' key), you can display supports replaced with the equivalent reaction:

Location, settlement, and orientation information can be set with high precision using the various support info inspector tables, a typical example of which is shown below:

Dr. Frame2D supports unilateral translational spring supports. This allows one to model lift off phenomena. The figure below illustrates the unilateral spring support option in action. The spring supports have been set up so that they act in compression only, and so the only non-zero reactions are for those inner supports near the load as is shown below.

To set the unilateral option for a given spring support, simply check the corresponding box in the spring support dialog.

Currently, only member spring supports can be made unilateral. Also, solution iteration is not automatic, so it is necessary that at least one load step be applied to get to a consistent state (simply selecting a load and using the cursor key to bump its magnitude up and then down again is sufficient). This is mainly an issue when opening a saved file or when switching between load combinations.

If the loading is such that a structure with unilateral springs goes unstable (e.g., due to overturning), then the structure will not return to a stable condition automatically even if the loads are returned to a stable state. To restore the structure's ability to track the loading, make one of the unilateral springs non-unilateral and adjust the loading so that this spring shows a non-uplift reaction. You then can put the changed spring support's setting back to unilateral on and continue.

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