I would like some help setting up a bolt connection (FEMAP/NASTRAN)

[Gus_203]

I'm currently following this tutorial on bolted connections (

https://www.youtube.com/watch?v=ZsE14nDOTEM),

however I get a fatal error "RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL". I've checked Bailout button and I can see that the structure is not behaving as it should

.

I tried adding a restriction on the lateral surfaces (restricting the lateral movement), but I don't know why I kept getting the same results (but I don't get the fatal error, even without Bailout).

Should I add any extra information to my post?

I'm working on this tutorial because I'm going to analyse a structure that has a lot of flange connections and I wanted to do a simple example before heading to a more complex problem.

Thanks in advance!

 

[karachun]

Should I add any extra information to my post?

Yes, Femap modell will be fine.

 

[Vitalii]

In your first case the upper part has no restrictions for rotation about the hole axis. Even though there seems to be no load that would cause such rotation, there is. Your model might be not absolutely symmetrical about XY plane. It looks symmetrical but nothing is absolute in PC (e.g. user value of 1 can be represented as 0.9999…99 or 1.000…01 in PC memory). So a tiny (and negligible) bending moment can exist and cause infinite rotation in linear analysis (error RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL).

In your second case I believe you applied additional constrains to the upper part and there should not be any rotation in the upper part. However the bolt itself still can spin about its axis since there is no restrictions on it. So bolt rotation can cause “RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL”. Try to prohibit bolt spin somehow.