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Approach 1 - assigning releases to shell elements
The latest versions of CSI programs allow to assign edge releases to the edge of shell elements via the Assign menu command for shell elements. This is the most convenient approach to assign simply supported shells. However, if more refined control is needed, then the additional approached described below can be used.
Approach 2 - connectivity via links
Shells may be modeled as simply supported shells by inserting short links between the slab and its supporting members. These links would be fixed for translational degrees of freedom (DOF), and free for rotational. This procedure results in a model which may be checked easily, since all links are readily visible.
Approach 3 - disconnect joints and apply constraints
An alternative procedure is to disconnect the joints and then use constraints to constrain only the translational DOF as follows:
- At each support location, disconnect all joints which connect the slab to adjoining members by selecting Edit > Edit Points > Disconnect. This will replace each single joint with two or more independent joints, one for each coincident member.
- If necessary, consolidate these disconnected joints such that adjacent slab objects share a common joint, and adjacent supporting members share a common joint.
- For each of these consolidated joints, define a body constraint, equal constraint, or weld constraint among UX, UY and UZ DOF.
- Ensure that the mesh for the simply supported shell matches that for the supporting system.
Approach 4 - offset shell element and apply weld constraint
Approaches 2 and 3 can be time consuming, especially for large models. A more efficient approach might be a combination of approaches 2 and 3 as follows:
- Select shell elements to modeled as simply supported.
- Move the selected shell elements by a small distance, say A, in a direction perpendicular to their plane (or approximately in this direction for more complex geometries).
- Select joints along the edges to be modeled as simply supported and include joints on both the moved shell elements and their adjacent shell elements. Apply weld constraint to the selected joints, using a tolerance slightly greater than A and constrain only translational Degrees of Freedom.
- Select joints along the edges to be modeled as fixed and include joints on both the moved shell elements and their adjacent shell elements. Apply weld constraint to the selected joints, using a tolerance slightly greater than A and constrain all Degrees of Freedom.
See Also
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You could model shell elements as simply supported by inserting short [links|kb:Link] between the slab and the supporting elements. These links would be fixed for translational [degrees of freedom|kb:DOF] and free for all rotational degrees of freedom.
Alternative procedure would be to disconnect the joints and then use constraints to constrain only translational degrees of freedom as follows:
* At each support location, disconnect all joints that connect the slab to the wall using the "Edit > Edit Points > Disconnect" menu command. This will replace each single joint with two (or more) independent joints, one joint for each connected element.
* Consolidate these disconnected joints, such that adjacent wall element share a common joint and adjacent slab elements share a common joint.
* Define [Body|kb:Body constraint], [Equal constraint|kb:Equal constraint], or [Weld constraint|kb:weld constraint] with UX, UY and UZ degrees of freedom for each pair of resulting joints, one joint on the deck and the other joint on the pier.
The first procedure will results in a model that can be easily visually checked as all the links will be readily visible, which is not the case for the alternative approach. Also, the mesh for the wall and the mesh for the slab should match for the alternative approach.
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Related Incidents:
* {incident:no=24990|comment=Slab moment release (good detailed example!)}
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