Encountering multiple errors with Direct Analysis Method and P-Delta calculations

[joshua_faigel]

I have included the structural model in this post

the model is supposed to have braced frames in the X direction and moment frames in the Y axis, I am encountering the following errors:

"Matrix is not positive definite - critical load may have been exceeded"

"No convergence of nonlinear problem"

I have read other forum posts regarding these issues and I have been unable to resolve them

[Krzysztof_Wasik]

Hi @joshua_faigel 

Dead loads applied together (for example in combination 17 (but also for others) causes structure buckling in ZX plane

For instance for combination 17 buckling coefficient is 0.9 (buckling load exceeded). Refer to buckling form below

This is the rason for matrix not positive definite.

I would revcommend the following

- add rigid diaphragm in slabs levels (to prevent structure  from buckling). It can be done by definind panel with slab-rigid diaphragm on stories levels.

example

- delete large displacement analysis (from combinations 16 to 23) ,leave only Pdelta, used also for DAM analysis

- set in nonlinear analysis parameters the following parameters (for no DAM combinations and DAM analysis).

After those modifications model should converge for both regular and DAM analysis

-