Gaplink / pounding

[abdellah]

Dear Seismosoft,

I am modeling 2 adjacent frames and connected them with a gap-hook element to model the expansion joint. I started a dynamic time history analysis.
1. Pounding is in one direction therefore,therefore, I modified the Gap-Hook element to take displacements in one direction and zeroed the other
2. I am confused about the directions of the defined spacing.
when i check the displacement of the two adjacent nodes, i dont know which of the signs represent the closing movement and which is the sign for the frames going apart.
3. Is there a way for intoducing a small stifness for the zero stifness parts in the gap-hook element.


Best regards,
Amr

[ricardomonteiro]

Hi abdellah,
1. If you wish to assume that no pounding occurs in one of the directions, you need to assum a large displacement in that direction, for the stiffness of the gap element to become 'infinite', and not as you are doing: zero-displacement;

2. The sign of the movement of the gap-hook is related, I believe, to the way you defined the nodes of the element. Referring to SeismoStruct help, the relative displacement will be the difference between displacements of nodes n2 and n1 (n2-n1). If it's negative, then the gap will assume its behaviour for the negative side, and otherwise, if the difference is positive.
If you still find it hard to understand I recommend you to test a simple example, with two linked elements, just for you to understand better the link working mode.

3. If I understood your question well, when you want to introduce a non-zero residual stiffness to the initial part of the gap's constitutive law, the element will then become a bilinear symetric or asymetric curve behaving element, bl_sym or bl_asm, don't you think?

I hope I having been useful.
Ricardo

[abdellah]

Thank You Ricardo
1. I think i was understanding the concept of the constitutive law of the Gap-element wrong, as i understand it now, the gap elemnt represents the distance between the two frames (Positive while moving wright and then pounding occurs and negative while moving left and then pounding occurs, for example)

3. Yes i want to introduce a small residual stiffness till the gap closes and then it increses like in the gap element.
but maybe i can try a bilinear symetric element, but i have to be sure the when the gap closes, at that point, the stiffness has to be so high that it will take no deflection any more. or what do you think ?

[ricardomonteiro]

Yes, abdellah, I believe it to be possible that way. I mean, once you assign an extremely high stiffness to the second branch of your bl_sym element, I suppose there will be no actual difference to the gap_hook element behaviour.

I again suggest that you can easily check it with a simple model, controlling the response of the two connected nodes to see if it has the intended behaviour.

Please let us know if you do so.
Ricardo