how to model chord rotation for plastic hinges

[mohamad reza]

how can i model chord rotation for concrete members ?such as chord rotation models that have been suggested in FEMA356(asce41) .i would like to concentrate plastic hinges in end of members and check it with acceptance criteria such as sap2000 program (or other program base plastic hinge model).i check the program and i found out seismostruct just can use fiber model .benefiting of using chord rotation model is you can consider bond slip and inclined crack and bond slip effect on it ,such as empirical terms which have been suggested in FRADIS (et.al 2001) for yield rotation and ultimate rotation base on this effect .in some topics have been talked about modeling the link element at the end joint of member for modeling chord rotation(for effect of bond slip and etc.).i cant understand ,how program can use this link model combine with fiber element ?if add link (for modeling chord rotation) element in member simultaneously with fiber element(infirm FB) in concrete member, which of them are selected for characteristic of member for nonlinear analysis(e.g push over or time history),

at the end, is it correct using link element for modeling chord rotation ?

thank you

[huffte]

Hi mohamad reza. I believe you may be able to track chord rotations using performance criteria built into SeismoStruct in conjunction with either:

(a)links at the ends of elastic column elements or
(b)inelastic column elements

I do not think you will need both links and inelastic columns. The link is just a way of concentrating the plasticity instead of modeling distributed plasticity.

You might also look into the inelastic plastic hinge element. Do a help system search on 'plastic hinge'.

You can also find details of the 'chord rotation' performance criterion with a help system search.

Best of luck mohamad.

[mohamad reza]

thank you huffte, can i follow your tips for beams?and can link elements consider axial load-moment interaction specially in plastic hinges in columns?

[huffte]

This is a good point that you make mohamad reza.

I do not believe that you will be able to consider axial load-moment interaction if you choose to use link elements.

This would be a good reason to begin experimanting with infrmFB, infrmDB, or infrmFBPH elements, in which cases the interaction would be implicit with the formulation, I believe. This might be the better choice for this reason. You could still impose a chord rotation performance driterion with any of these elements.

[mohamad reza]

thank you huffte

if i use link element how many nodes should i define for element,i asked this question because program default define nodes in intersection of bream and columns and if i want to assign moment rotation for beam there is only one node at intersection of 4 element (two column above and below and 2 beam at left and right of node).what should i do ?i want define curve for beam and column but there is judt one point at intersection.

[huffte]

mohamad, for each link element you will need to define 4 nodes. So you will have to create additional nodes if you generated a model from the wizard.

So let's say for example, that you are at the corner of a floor with 2 beams framing in and 2 columns framing in. You will have a node, call it n1, to which the beams connect. You will have another node, cal it n2, at the exact same coordinates as n1. The upper column will have it's end connected to n2, and the upper link will have n1 and n2 as its first 2 nodes, with it's 3rd node being the node at the top of the upper column and the 4th node being in the direction of one of the beams.

You will have yet another node, call it n3, at the exact same coordinates as n1 and n2. n3 will have the top of the lower column connected. n1 and n3 will define the first 2 nodes of the lower link.

You have 18 link types from which to choose, but I suspect you will want to try either the bi-linear kinematic link, the Takeda type link, or the plastic link, but there are lots of other options. The bilinear kinematic and plastic are the ones I have had success with. In the Help system, do a search on "Link" to get details of all the available types.

Best of luck mohamad.

[mohamad reza]

thank you huffte

i cant understand carefully , so could you send me an example that i can see how connect links to nodes and define nodes?i read help but it is not clearly explain how to connect links or maybe i could not understand well

i appreciate you for helping me and devote your time for answering my questions.

this is my email : mohamad.akhavanpur@gmail.com

[huffte]

Regarding your concrete moment frame, mohamad, I believe that your use of the rigid diaphragm constraints in the 2D analysis is unnecessary.

And for the Equal DOF assumption, I don't think that the "ry" degree of freedom needs to be included in the constraint. I assume you are including "x" in the constraint because your assumption is that a concrete slab will force the column tops to move together. This, in itself, may not even be necessary. I think you wil just have to look at the details of how the building is constructed and decide if, in fact, the slab will essentially force all nodes at a floor level move together in the x-direction.

In summary, I personally would recommend avoiding the Rigid Diaphragm constraint for the 2D analysis and either use the Equal DOF constraint with "ry" removed, or lose constraints altogether. Note that these constraints will effectively remove any axial load form the beams.

[ESTRUCTO]

Hi.

I want to use the infrmFBPH model for concrete members, but I do not know what hysteretic curve is used by seismostruct to define the plastic hinge F-D curve (MIMK, for example). I know that infrmDBPH element class uses by deffault MIMK_bilin curve.

Thanks.

[seismosoft]

The infrmFBPH model is a distributed plasticity model on the section level. The section if discretized to fibers and each fiber has its own material law (for steel, unconfined and confined concrete). Please refer to the manual and the help of the program.
Seismosoft Support