Run the same RISA-3D Model but get different result

[Huaxingxing]

Hello everyone,

I am so confused right now, I have a 75ft-tall CMU shear wall system building in RISA-3D, and I would like to know the drift. First I run the envelop and get 2" drift in LC 170, and I run the LC 170 drift becomes 0.3". I really don't understand here, is that supposed to give me the same result?

Does anyone have the same problem with me?

Thanks in advance.

 

[JAE]

Your envelope drift would include all load combinations that are checked on the Load Combination sheet.
These may include load combinations that produce MORE drift than LC 170.

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[Huaxingxing]

Thanks for your reply. I was not clear in my question, but the MAX drift happens in LC 170, if I just run LC 170, should I get the same result as envelope?

 

[JoshPlumSE]

There are a few caveats.

The first one: Is the model really the same for both solutions?

The reason why I ask is some elements have varying stiffness. For example: When you have masonry or wood shear walls, the program goes through the "optimization" of these walls. If one run resulted in a fully grouted wall and the next run resulted in a partially grouted wall, then the stiffness would be different.

This is very difficult for users to keep track of. However, if you go to the (Global) Model Settings and select the Solution tab there is a series of settings related to wall optimization. If you manipulate those setting you should be able to force the same stiffness for both runs.

2nd Caveat: You're assuming the envelope solution reported to you the correct load combination. You might try running a batch instead of an envelope to make sure it produces the same results. I've seen older (and since corrected) bugs where sorting spreadsheets could cause results to jumble up a bit.

If the issue still persists after investigating it based on my suggestions, obviously, you probably should contact RISA/ Nemetschek tech support.

 

[Huaxingxing]

Hi JoshPlum, that's a really insightful reply thank you, I will take a look.
Also, I have already contacted RISA tech support and uploaded the model to them. Hopefully I will get a response in the next few hours.
I will keep you guys posted, thanks for replying.