Shell transition element in ADINA 1

[tuanphamanh]

Hello,

I’m using Adina to model dynamic behaviours of an integral abutment bridge. In my model there are shell transition elements to model the connection between steel girder and the integral abutment (shell to solid intersections). The original model works ok with dynamic analysis.

Then I induced the damage to the model by removing one volume in the deck of the bridge and did the dynamic analysis again. The surfaces and nodes were renumbered by ADIA. I corrected the nodes, surfaces number problem for the damaged model. But this time, it didn’t work, the damaged model stopped and reported this error.

“A STIFFNESS DIAGONAL ELEMENT IS NOT POSITIVE BEFORE DECOMPOSITION.
NODE NUMBER = 131 DEGREE OF FREEDOM= X-ROTATION
EQUATION NUMBER= 262 THE ELEMENT VALUE= 0.000000000000E+00
*** ERROR NO. A1601 ***

Frequency-negative/zero diagonal element before decomposition.Incorrect model”


And if I remove the transition elements, the damaged model works ok. Is there any suggestion or help for me please?

 

[crisb]

Examine the error message carefully. Where is node 131? Is it on one of the transition shell elements? By default ADINA automatically assigns the number of DOFs to shell midsurface nodes. Maybe you need to set it manually for this element?

 

[tuanphamanh]

Thanks for your help.

I locate the node. It’s in the transition shell elements. Last time, by default ADINA automatically assigns 5 degrees of freedom to the midsurface nodes. It’s should be 6 degrees of freedom because :

+ Nodes along the edge of shell elements intersecting at an angle (Abutment and Steel girder).
+ They also belong to abutment (3 D solid elements).
+ Rigid links (between the steel girder and the deck) are connected to the nodes.

As you suggest I manually assign 6 degrees of freedom to a node through Mode> Shell Midsurface Nodes. But I didn’t work. Adina reports the same error. And what is the problem with degree of freedom of node 131.

Do you have any suggestion for me?

 

[crisb]

What elements connected to node 131, and the geometry? Is the arrangement at 131 the same as at other nodes that dont report an error?
The error message is specific to frequency analysis, can you do a static analysis without an error?
I would try applying a rigid link or constraint at that node just to understand what is going on (not to leave it there).

 

[crisb]

One more question. You mentioned a rigid link. Is the master attached to one of your "damaged" elements and if so do the remaining elements provide 6DOF at the node. Remember 3D elements alone only have 3DOF.

 

[tuanphamanh]

Thanks man,

I highly appreciate your help. I figure out the problem and have already fixed it.