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SPRING INSTEAD OF LINK-ELEMENT
2

SPRING INSTEAD OF LINK-ELEMENT

SPRING INSTEAD OF LINK-ELEMENT

(OP)

Dear Sirs,

so far we us linear link elements to simulate a spring.

The problem of the link element is that is also transfers shear forces / moments. E.g. I define a linear spring link element with stiffnesses in all three (x,y,z,) directions.
If I conncect two joints (with different z values)with the described link-element there are moments at one joint due to the vertical distance of the joints. But I just want to transfer forces (at each direction one force Fx, Fy, Fz)


Is there any other possibility to simulate a spring in SAP2000 ?

FYI: we are using SAP2000 Version 10.1.3

Thanks in advance
Daniel

RE: SPRING INSTEAD OF LINK-ELEMENT

Dan, I did a quick check and the J end of the link is where the moment due to shear seems to be taken as zero whereas the I end takes moment. So it's a problem/bug from what I can tell, but it appears to depend on what direction you draw your link.

Report it to support@csiberkeley.com

RE: SPRING INSTEAD OF LINK-ELEMENT

(OP)
Thanks for your answer, but I do not think its a bug I think the "link - element" is not the right element I want to use. I want "pure" stiffness behaviour in the 3 directions without shear / moment transfer.

regards,
Dan

RE: SPRING INSTEAD OF LINK-ELEMENT

I should have included more info in my last reply. In my little test model I created a a column fixed at the base, and from the top of the column, I drew a 2 pt linear (spring) link with a length of 1 foot vertically above the column. I defined the link with stiffness in 1, 2, 3 local directions (X, Y, Z) but no moment/rotational stiffness. I then assigned a lateral joint load to the top of the link, which was 1 ft away from the top of the column. Depending on the direction I drew the link, from top to bottom or bottom to top, it either did or didn't transfer moment. The "J" end of the link had to be the end connected to the column to avoid transferring moment. There is no way that I can see to make the link transfer load like a true pinned column or beam, which would not transfer moment on either end. That is what I think you want and expected.

For now, I still think this is a bug, because if I define a link with stiffness only in X, Y, Z directions, I would expect the 2 point link to behave like a pin connection - no moment transfered on either end, but SAP's link element insists on transferring moment on one end, even with zero stiffness in rotational directions.

My only suggestion to you is to define a general frame element with equivalent stiffness as your link and model the frame as pinned.  

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