Instabiliy of Structure, Issues and Fixs

[NguyenTTU]

Hi guys,

I know sometimes you guys will get a big issue that is instability of model. It will take alot of time to fix this problem. I would like to share you my experience to see and fix this problem.

As you known, there are 3 types of instability. Type 1 and Type 2 are more easily than TYPE 3.

Type 1 and Type 2, this two type is almost from USER's definition.

Example: You've made a BAR with pin-end connected to other bars. However, The bar is released  BOTH-END with PIN-PIN.

Type 3 comes from 3 major things below:

- USER DEFINITION:

- There is no connection between bar-to-bar. You just think 2 members connected together, but it does not connect together. They will have a big tolerance after computing.

For example: You see your beautiful structure on 3D view with bar-to-bar connection. However you will get a wrong here, even they have the same node on 3D. You should come to 2D as XZ plane or YZ plane, you will see some bars missing there due to tolerance.

- WRONG ASSIGN: This problem will be seen when structure calculation is completed. For example: Bar must be assigned with I-BEAM, but you assigned it with a ROD. Another, BAR is I-BEAM, you assigned the bar with TENSION ONLY.

- WEAK SPRING SUPPORT:  Collapsed Structure

How to see problems from 3 TYPES :

1. After calculation, go to RESULT -> Diagrams for Building... -> Go to tab DEFORMATION. Try to making deformation scale better, almost issue will be viewed clearly on the screen such as structure totally collapsed. Bar-to-bar not connected together,... 

This is a major reason for non-convergence problem.

2. Now you can view saperately your collpased part and correct your issues step-by-step.

Hope it can help you solve your problem quckly.

Best Regards

Tu Nguyen