topic Re: partial fixity in Robot Structural Analysis Forum

partial fixity

saclovitzky — Sun, 26 Jul 2015 12:21:51 GMT

Hello,

Regarding partial fixity of base(ie, 20% fixity), which is the right step in doing this;

1. provide partial end release to the column, or

2. directly provide partial fixity directly on the support(,ie 20% base fixity

2.1 by the way, how do you provide partial fixity on the base?

2.2 normally, to have a partial fixity on the base(ie, 20%), I normally provide values on the "rotation" of the base until the moment of the column (on the base) is approximately 20% of the moment at the top of the column, Is this correct(pls. see attached sketch).

Any ideas will be greatly appreciated.

Regards,s

Re: partial fixity

Anonymous — Sun, 26 Jul 2015 21:48:51 GMT

Read this post, http://forums.autodesk.com/t5/robot-structural-analysis/20-base-fixity/td-p/5737059

Re: partial fixity

saclovitzky — Mon, 27 Jul 2015 07:38:39 GMT

That's the reason why I have this question because of that thread.

Re: partial fixity

saclovitzky — Mon, 27 Jul 2015 14:59:00 GMT

Hello Artur,

Can you comment on this?

Regards,

Re: partial fixity

Artur.Kosakowski — Tue, 28 Jul 2015 07:44:00 GMT

I think you should use the first option. There is no functionality in which you can tell the program that the check at the bottom node should additionally be done for bending equal to 20% of the moment in the top node but you may run such check manually entering the required value of bending in both the steel design and in the steel connection modules of Robot.

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Re: partial fixity

saclovitzky — Fri, 31 Jul 2015 10:55:20 GMT

Hello Artur,

So, basically, the general rule for having a 20% partial fixity at the base, is to have a partial releases at the bottom node of a column(ie, 20%) and the support on that column should be "fixed". Is this correct?

Also, why we cannot directly create a fixed support which allows partial fixity(ie, 20%, 10% etc.)?

I also discovered that my previous practice is wrong(comparing top node moment and bottom node moment as a basis for partial fixity)

Regards,

Ramon Saclolo

Re: partial fixity

Artur.Kosakowski — Fri, 31 Jul 2015 11:54:23 GMT

So, basically, the general rule for having a 20% partial fixity at the base, is to have a partial releases at the bottom node of a column(ie, 20%) and the support on that column should be "fixed". Is this correct?

Yes, it is.

Also, why we cannot directly create a fixed support which allows partial fixity(ie, 20%, 10% etc.)?

How would you calculate this "partial fixity: for a support? For a support you may define the relation between bending moment and rotation of a node instead.

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Re: partial fixity

saclovitzky — Fri, 31 Jul 2015 12:10:58 GMT

Hello,

I've got this idea, from my portal frame program, wherein, you just simply choose a support with 10% and 20% fixity.

Regards,

Re: partial fixity

Rafacascudo — Fri, 31 Jul 2015 12:15:29 GMT

Ramon,

You can set a limit to the support moment (or any other available nonlinear function) using non-linear support type.

But it is very possible , after RSA calculations ,that the top moment will not remain the same