Auto Edge Constraints

Form: Shell Assignments - Auto Edge Constraints

Typically in finite element analysis, shell elements are connected to other elements at corner joints only. When an element does not frame into the corner joint of a shell element, but instead frames into the edge of the shell element, no connection exists between the element and the shell element. The ETABS auto edge constraints feature can be used to specify that elements framing into the edge of a shell element be connected to the shell element. ETABS internally takes care of connection between the elements by constraining joints lying along an edge of the shell element to move with that edge of the element.

Apply Auto Edge Constraint as follows:

Select the shell object(s) to which auto line constraints are to be assigned.
Click the Assign menu > Shell > Auto Edge Constraints command to access the Shell Assignments - Auto Edge Constraints form.
Choose the appropriate options:

Do Not Create Edge Constraints option. When this option is selected, ETABS will not constrain joints along the edges of the shell elements to move with the edges of another element. Use this option to remove existing auto edge constraint assignments from selected shells.
Create Edge Constraints around options. Note that by default, this option and both sub options are selected. Select both or deselect either of the following sub options:
- Walls check box. When this check box is checked, ETABS applies the edge constraints along the edges of wall type shell objects.
- Floors check box. When this check box is checked, ETABS applies the edge constraints along the edges of floor type shell objects.
- Apply to Full Structure (not just Selection) check box. ETABS applies the edge constraints along the edges of all floor and wall type shell objects in the model even if they were not selected before the command was clicked. This check box is checked by default so be use consider this action before completing the next step.

Click the Apply button to complete the assignment.

When the Apply button is used, the Shell Assignment - Auto Edge Constraints form will remain open until it is closed by clicking the Close button. This allows selection of another shell object(s), to which a different assignments can be made.

If only one assignment is being made to only one set of selected objects, the OK button can be used to both apply the assignment and close the form.

IMPORTANT NOTE: Edge constraints transfer load from intermediate joints to corner joints along the edge of a shell. Applying an edge constraint along an edge that is co-linear with a frame, cable, tendon or link object can result in load being transferred by the edge constraint instead of by the object. Using edge constraints in these locations should be avoided if detailed results in the frame/cable/tendon/link objects are of interest. In particular, frame design results could be affected, and may be unconservative. Frame/cable/tendon/link objects with only one joint connected to the edge are not affected, and in fact, one of the advantages of using edge constraints is to connect such elements to a coarse shell mesh, provided that detailed local stresses in the shells are not needed. When frame/cable/tendon/link objects are co-linear with an edge constraint, the overall effect of the object on the model is captured, but local response may not be accurate.