I ran a non linear model on a 2D frame, and gradually added non-linear moment hinges on the members near the points of highest stress to simulated the collapse from plastic hinges.
The highest global stress is given as a bar and a node location, so I had to add non-linear hinges on the bar at a relative distance that was close to the node but not on the node itself.
When I got my structure to become unstable it gave the error message of "instability (of tyoe 3) at node 32 in direction Ry" I tried to find out which location this instability occured so I had the program display the number of calculation points and it shows 2 different numnbers at each hinge and I cannot find a pattern to the numbering. Also, the numbers are as low as 3 and as high as 90 but not all of the numbers in between these two are on the screen.
Can anyone tell me how the numbering works for non-linear hinges and what the instability at node 32 means.
1. Ful Newton Raphson should be set for these cases:
2. Define properly nonlinear function, try to avoid relative definition of limits.
My example below
3. or delete hinges from bottom of the columns.