partial fixity

[saclovitzky]

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

[Anonymous]

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

[saclovitzky]

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

[saclovitzky]

Hello Artur,

Can you comment on this?

Regards,

[Artur.Kosakowski]

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.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[saclovitzky]

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

[Artur.Kosakowski]

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. 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[saclovitzky]

Hello,

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

Regards,

[Rafacascudo · Accepted solution]

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