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"Specified displacement of support" with other load case like nodal, element loads in a same Load Case

Question:

Hello,

I would like to analyze the behavior of the system during the theoretical settlement of the support by a given value. Therefore, I add a load case using the Specified Displacement function. 
Now I would like to analyze this load case together with other load cases, so I create a load combination and using the Using Load Combinations function I convert this combination to a static load case. The program doesn't show any errors and counts this layout without any problems. 
Problems arise when we move on to analyzing the work of the structure.
Starting with the internal forces, there are no moments at the support where the extortion is performed and a very large reaction is generated at the point where the support is connected to the curve. 


Answer:

Dear User,

Before going to the solution let me first explain the reason behind this issue.

In the case of "Specific Displacements of Support," the program internally creates the nodal loads that would create the required displacement at that particular node/support but at the same time, it also limits the displacement of that node by the specified value. For individual load case there would be no issues in the results but if another load is considered along with specified displacement load even then the overall displacement of that node will be equal to the specified one. In another term, we can say after that displacement that node will become rigid in specified displacement direction. See the following example to understand this procedure more clearly:- 

but if this specified displacement load is combined with a different nodal force of 30kN in a same load case then see the reaction results. 


Therefore it is not suggested to combine any other loads in the same load case along with the specified displacement.

Now let's discuss the solution for this, rather then including specified displacement in the main load case, reaction results of individual specified displacement load case can be included as a point loads in the main load case. 


Kindly find the sample model attached herewith. 

Regards,
Kaushal Mittal
Technical Support Engineer

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Creation date: 8/6/2020 2:37 AM (Kaushal Mittal)      Updated: 9/16/2020 1:40 PM (dklee@midasit.com)
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