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Live Load model analysis showing moment restraint in bearings that should not have moment restraint

Creation date: 10/17/2018 10:16 PM    Updated: 10/18/2018 7:47 AM
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Question:

Hello MIDAS technical support,

I have created a model for a three span continuous steel girder bridge.  It is a 2D model with composite beam elements used for the girders.  I have created two different files, one for the dead load and one for the live load.  The bearings were defined the same way in both of the models.  I used Boundary>Define Supports to define the bearings.  For the fixed bearings (at pier 2) I fixed Dx, Dy, and Dz while leaving all rotation (Rx, Ry, Rz, Rw) free to rotate.  For the expansion bearings (both abutments and pier 1), I fixed Dy and Dz while leaving the rest of the degrees of freedom free (Dx, Rx, Ry, Rz, Rw).

As I mentioned previously, the bearings are defined the same way for both the live load and the dead load model.  In the dead load model the bearings appear to be working properly.  After analysis, the dead load model shows forces in the fixed degrees of freedom, while showing no force in the released degrees of freedom.  Which is correct.  However, in the live load model the pier bearing locations (interior supports) are showing forces in the rotational degrees of freedom for both piers even though the program shows the rotation should be free to move.

I believe the dead load model is correct and the live load model is incorrect.  Can you please tell me how to fix my live load model so that the bearings are correctly modeled to allow all rotation.  Is this an issue with the way I have modeled the structure?  Is this an issue with the MIDAS software?  I loosely followed your tutorials for similar style bridges, but please tell me if I have modeled something wrong which is creating this issue in MIDAS.

I have attached both my dead load file (which is acting correctly) and my live load file (which is not acting correctly).

Also, I realize that everyone's question is important.  But I am very behind on my deadline for this project, so if you could provide me with your thoughts as quickly as possible, I would greatly appreciate it.  Otherwise I may miss my deadline.  Please feel free to call me if anything in this email is unclear, or if explaining the issue over the phone would be easier.

Thank you very much.



Answer:

Hello,

Thanks for writing to us!
The modelling in this case is perfect!
At our end, the behavior is also as expected.  I'd appreciate if you could share the screenshot of the discrepancy noted at your end.


Regards,
Nandeep
Technical Manager, MIDAS


I am not sure what to tell you.  My models are showing moments there.  Is it possibly because I am running an older version?  I am not sure if mine is up to date.  Here are my screenshots.

Thanks for looking into this so quickly.  I hope the screenshots help.

Thanks



Hello,

The latest version of midas Civil is 2019 v1.1.  If you want to upgrade to the latest version, kindly download the same from our website en.midasuser.com.  Kindly note that you must be under annual maintenance contract if you need to use this version.
The version I checked in is Civil 2017 v2.2.  If you need to upgrade to the last release of Civil 2017 version, kindly do so by following the steps below to apply the patch.

Patch Link:  https://drive.google.com/file/d/1ePXtrfhhxqopF0KJQ9kM1dTA43e67gKp/view?usp=sharing

To apply the patch, please follow the steps below:
1) Download the patch by Clicking on above patch link
2) Extract the content of the file
3) Paste them at the location where midas Civil is installed. Default location is - C:\Program Files\ MIDAS\midas Civil
4) When prompted to replace existing files, please click yes
5) Restart computer, Done!

Kindly let us know if further assistance would be required.

Regards,
Nandeep
Technical Manager, MIDAS


I loaded 2019 v1.1 and the moment restraints are gone.  So it was an issue with running the live load through the old version.  I just wanted to let you know the issue in case it comes up again with someone else.  

I appreciate the quick effort and prompt responses.  I know I opened this ticket again, but you can feel free to close it.  I just needed to say thanks for the help before we were done.



Hello,

Really glad this helped.  Kindly let us know if further assistance is required. :)

Regards,
Nandeep
Technical Manager, MIDAS
Midas Model Dead Load.mcb
Midas Model Live Load.mcb
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DataImage35.png
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