Working with Joints

Dr. Frame2D has various facilities for creating and removing, selecting, modifying and displaying joints.

Dr. Frame2D treats joints as distinct entities, with fixity and constraint conditions defined by the framing-in members and supports. The following examples illustrate several representative cases:

Pinned Joints: all members and supports rotate independently
Rigid Joints: all members and supports share the same rotation
Hybrid Joints: some members and joints rotate independently, while others are connected rigidly (in the first example shown, the support is pinned while the members are rigidly connected; in the second example the horizontal and diagonal members are simply-framed while the column is continuous through the joint.

Partial fixity can be achieved by selecting a member, then setting an end condition as hinged in the Property Inspector and associating an appropriate rotational stiffness there.

Creating & Removing Joints

In general, joints are created automatically at the junction of elements and/or supports. It is not necessary (or possible) to create joints in isolation. Similarly, joints are automatically removed when their associated members and/or supports are deleted. Joints cannot be deleted directly.

Selecting Joints

Joints can be selected either by clicking on them with the Select Tool, or by enclosing them in a Select Tool selection rectangle (i.e., the result of a click and area-drag).

Modifying Joints

In the case of joints, modification boils down to relocation. One can relocate joints either by selecting and dragging them as desired (with grid snapping on, joints will snap accordingly--holding down the control key while dragging temporarily disables snapping), or by means of the Property Inspector when a Joint is selected.

As indicated, you can enter location data directly. You can also observe the current displacement and rotation at the joint in question.

Display Options for Joints

There are several display/modeling options for joints.

1. All joints can be automatically labeled by choosing Options>Joint & Support Display>Show Joint Labels. A typical result will look as follows:





2. Each joint can be automatically isolated as a free body. This option is available via the Modeling>Isolate Joints (ctrl/cmd-J) command, and is discussed further in the section Working with the X-ray Tool.
3. Labels can be applied to joints with the Label Tool indicating their current displacements. See the section on labels for more information.
4. The text pane at the bottom of the display window summarizes joint displacements and support reactions. Joints can be selected in either the text pane or the display pane.