Plastic hinge which considers P-M interaction

[hshoar]

Hello

I need to define plastic hinges for a 2D steel structure. I am investigating progressive collapse resistance capacity of x-braced steel dual
systems.
The only material which seems to be right according to progressive collapse guidelines is Modified Ibarra-Medina-Krawinklerear Bilin Material material.
I can model rotational springs using that material for the beams, but, for the columns I need to consider P-M interaction.
How can I define a plastic hinge which has the IMK material and considers the PM interaction?
Do I have to use another material?

Thank you In advance.

[mhscott]

Yes, you would need to use a different material. Either switch to fiber sections or take a look at the yieldSurface section models. The former is well documented, but not the latter.

[hshoar]

Thank you Dear Prof. Scott
As you mentioned here and in my previous post, the yieldSurface sections are not documented. I took a look at source code but I couldn't use it.
Can you please explain me how can I use fiber o yieldsurface sections?
I appreciate your quick and informative replies.

[mhscott]

You'll have to use a uniaxial steel model that has cyclic degradation. Also, the corotational geometric transformatin should be used to simulate collapse due to geometric nonlinearity. There was a recent post on brace frame modeling and a link to an OpenSees model by Uriz and Mahin

http://peer.berkeley.edu/publications/p ... ZMahin.pdf

[hshoar]

Dear Prof. Scot
maybe I'm asking repetitive questions, but, its because I'm really confused:-??
I defined the column with elasticBeamColumn and zerlongth elemnts to demonstrate plastic behavior. A steel column with square hollow section which has two zerolength element at ends as concentrated plastic hinge.
If I have to use fiber section for zerolength elements, which material I should use to achieve this goal, while I have to satisfy the guidelines about hinge properties which defines a force-deformation or moment-rotation curve?
another issue is that how is the force-deformation and moment-rotation curve related to interaction curve?
and the last question is that using elasticBeamColumn in this case is right or not?
Always appreciate your helps!

[mhscott]

Even though it's commonly done, using fiber sections inside zero length elements at the ends of an elastic beam is not a good idea. The reason is there has to be some length associated with the section response. Fiber models give you moment-curvature, not moment-rotation, so some fudging is necessary if you go the zero length fiber section route.

In my previous post, I meant that you should use fiber sections inside a nonlinear beam element, like beamWithHinges or forceBeamColumn, instead of an elasticBeamColumn with zero length springs. Sorry for the confusion.

[hshoar]

The reason I've decided to use elasticBeamColumn with zerloength elemnts as hinges was that I can record the rotation of zerolength element and compare it with allowable values in GSA. How can I get the rotation of plastic hinges formed in a beamWithHinges?
And I'm still have those questions about using fiber sections. actually the reason of my confusion is pm interaction!

[mhscott]

With fiber sections you get the P-M interaction automatically. There is a recorder option for the beamWithHinges called 'plasticDeformation' which will give you the plastic rotations.

[hshoar]

Thank you very much dear Prof. Scott
for the new beamWithHinges is it right to use steel01 in fiber sections of both hinges and interior section of element?
is steel 01 has cyclic degradation?
I'm not sure using steel01 is the right material for progressive collapse, because I think I need to model the strength loss for load redistribution. am I right?
Or maybe I can use steel01 with MinMax material.

[mhscott]

You will have to develop your model and try different things. Good luck!