Singularity warning - cause?
Question:
Dear Sir / Madame,
Answer:
Hi,
Dear Sir / Madame,
When running the model attached, I get three warning that some nodes may be singular in the direction Rx.
ENTRY STATIC ANALYSIS
MULTI-FRONTAL SOLUTION HAS BEEN PERFORMED 50 % .
WARNING : NODE NO. 99 RX DOF MAY BE SINGULAR.
MULTI-FRONTAL SOLUTION HAS BEEN PERFORMED 70 % .
WARNING : NODE NO. 56 RX DOF MAY BE SINGULAR.
MULTI-FRONTAL SOLUTION HAS BEEN PERFORMED 90 % .
WARNING : NODE NO. 36 RX DOF MAY BE SINGULAR.
MULTI-FRONTAL SOLUTION HAS BEEN COMPLETED.
DISPLACEMENT/FORCE/STRESS OUTPUT.
ELEM. : 972 OF 972
-----------------------------------------S O L U T I O N T E R M I N A T E D
YOUR MIDAS JOB IS SUCCESSFULLY COMPLETED.......V:\Projects\2018\L118008\ENG\04-Calcs\Gantry 249\Midas Model\KXR Gantry 249 - Existing Gantry
TOTAL SOLUTION TIME..: 2.84 [SEC]
------------------------------------------------------------------------------
3 WARNING MESSAGES ARE FOUND.
PLEASE CHECK YOUR WARNING MESSAGE FILE :...Gantry 249\Midas Model\KXR Gantry 249 - Existing Gantry.OUT
I reviewed the model and the results and I can't find anything wrong.
Any chance you could shed some light on this?
Answer:
Hi,
As you see below, the top chord of the truss system is supported just by truss elements. Thus, the top chord has no resistance to the rotation about the X axis. If you assign point spring support with negligible rotational stiffness to any one node of the top chord, the warning will not appear.
Regards,
DK Lee
KXR Gantry 249 - Existing Gantry.mcb
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