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Change stiffness for different Load Cases

Question:

Hi,

I would like to apply stiffness scale factors to elements, links and spring supports for different load cases. So I can, for example, use cracked and uncracked stiffness for the same elements within the same model, release bearings for certain load cases and apply upper bound and lower bound spring stiffness to supports. I would also like to be able to include loads from particular construction stages within load combinations. My understanding is that for sections, I can turn boundary group scale factors on/off in construction stages and also turn different links/springs on/off in construction stages. However, this is not ideal because, as far as I am aware, it is not possible to include results from a particular construction stage within a load combination. I would also like the stiffness scale factors to be available post-CS with the moving load analysis.

Can you confirm that midas cannot apply stiffness scale factors in PostCS and that it is not possible to include loads from particular C.S stages within load combinations?

Kind regards,


Answer:

Hello ,

You can use the Analysis >> Boundary Change Assignment to Load Case/Analysis. With this function you can assign different boundary conditions, like supports, springs, stiffness scale factors, etc., to be considered for different types of analysis or individual load cases. You can find information on this in the Online Manual:


As for the results of a given stage to be included in a Load Combination, you are correct, this is not possible for any stage. Only the results from the last construction stage are available to combine in the Load Combinations. However, you can use Analysis >> Construction Stage Analysis Control, and the option "Final Stage" which will run the analysis only up to a given stage, and then the results from this stage become the CS output for the PostCS combinations. However, you can only do this for a single stage at a time, and you will need to re-run the model if you need another stage to be the final one.

Kind regards,
MIDAS Support

________________
Question 2:


Thank you for your response. 

For certain load cases, I would like my bearings to have zero stiffness. Would I be able to do this by applying general links at these locations with zero stiffness and assigning to the relevant load cases in Boundary Change Assignment to Load Case/Analysis? I notice that it is not possible to change the general links in the  same way as the other boundary conditions, as the following article attempts to explain: http://manual.midasuser.com/en_tw/civil/830/Start/04_Model/06_Boundaries/Change_General_Link_Properties.htm


I have one more question:

How can I set 'Change General Link Property' using the MCT Command Shell? I cannot find a command that is relevant. I have a huge number of general links that I would like to assign a 'change general link property' to and the only way that I currently see to do this is to do it one by one.

Kind regards,
_________________________
Answer 2:

Hello ,

To change a General Link Property for different Load Cases / Analysis Cases you need to use the Boundary >> General Link >> Change General Link Properties, as you have indicated. This functions allows you to assign a different link property to a single General Link definition and assign this to a Boundary Group. For example, you can define two different general link properties, one very stiff and one very soft. You can then use the stiff one to define the General Link as a base case, when you create the link.


Then using the Chang General Link Property you can set that using a chosen Boundary Group you can change this general link property to a new property.


Then in the Boundary Change Assignment you need to general a change set and assign this to the Load Case of interested to use this property:

If you then check the results you will see they reflect the change. We have attached a very simple model demonstrating the above, where the original link is very stiff and attracts all the load to the cantilever, while with the soft link the load on the right node goes to the support string below it (Load cases 1 and 2 are identical, but one uses the stiff and the other the soft General Ling)

For the quick definition in the MCT Command Shell:


Kind regards,
MIDAS Support

Creation date: 2/18/2020 3:24 PM (MIDAS_UK_IM)      Updated: 2/19/2020 2:00 AM (MIDAS_UK_IM)
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