topic Re: How to support a structure in only one direction in Robot Structural Analysis Forum

How to support a structure in only one direction

Anonymous — Thu, 26 Apr 2012 11:21:19 GMT

Thx for reading my post. Please see attached model. I would like to support the bottom surface og the footplate so that i can not move down in the -z direction but can only deflect upwards in the +z. This would mean that the footplate is only RESTRAINED for downwards deflection. This corresponds to the plate laying on a concrete block. How can add this kind of support?

Hope anyone can help

Re: How to support a structure in only one direction

Anonymous — Thu, 26 Apr 2012 11:42:40 GMT

Re: How to support a structure in only one direction

Anonymous — Fri, 04 May 2012 04:19:20 GMT

I am also having trouble with this, I am simply trying to model a post with a base bolted to ground and a load on the post, I wish to see the load on the bolt, but keep getting errors with the calculations, as the reaction at the bolt seems to change between tension and compression when in reality would always be in tension (i.e. trying to be pulled out of ground)

I have 2 loads that are equal but in opposite directions.

please help me.

Re: How to support a structure in only one direction

Anonymous — Fri, 04 May 2012 04:37:28 GMT

Just create 2 copies of the same thing and add supports to suit. See attached.

Your method seems a strange way to model this structure though......just my opinion of course.

Re: How to support a structure in only one direction

Anonymous — Fri, 04 May 2012 04:42:51 GMT

Thanks heaps, seems so obvious now.

I am very new to Robot and am learning by myself, i am very interested to hear another way to model this if you don't mind showing me. (although i fear it may be above what i know)

Thanks again.

Re: How to support a structure in only one direction

Anonymous — Fri, 04 May 2012 06:06:04 GMT

Also i have updated the model with correct dimensions and steel plate as base. (couldn't find steel plate before) FB???

cheers

Re: How to support a structure in only one direction

AlexDT — Fri, 04 May 2012 08:02:00 GMT

I'd like to do this to do this with a wall that is attached to another wall/column. I've been trying to make this work lineair release, but without succes. Could it be done? ... or may I not be understanding this fully

Re: How to support a structure in only one direction

Artur.Kosakowski — Mon, 07 May 2012 08:12:47 GMT

Alex,

What was the exact issue with your model?

Re: How to support a structure in only one direction

AlexDT — Mon, 07 May 2012 09:05:43 GMT

Hey rtur,

It is not really a problem, but was curious if that functin also applies to walls to walls (lineair release) to make a wall only bear pressure forces and then be ignored if its being pulled on.

Re: How to support a structure in only one direction

Artur.Kosakowski — Mon, 07 May 2012 09:12:07 GMT

Yes, it does.

Re: How to support a structure in only one direction

Anonymous — Thu, 10 May 2012 08:08:55 GMT

Hi Thx for the great answer :). I want to restrain the whole bottom surface of the footplate against movement in -z direction. When i do this, IT DOESENT WORK, it restrains all movements in the z- direction.the reason i want to restrain the whole bottom surface is because i want it to look that the footplate is "laying" on a concrete block.) please check attached

Re: How to support a structure in only one direction

Artur.Kosakowski — Thu, 10 May 2012 08:13:38 GMT

As you define the direction of the possible uplift you should set UZ+ instead of UZ-.

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.

Re: How to support a structure in only one direction

jo2ny — Wed, 27 Feb 2013 09:29:16 GMT

Hi,

I'm having also trouble with this kind of supports.

In my model (a relatively simple rectangular box shaped structure) I have several supports set to Uplift UZ+ and after the calculations I stil get some posive and some negative reactions in these kind of supports.

Even if I set the direction wrong, they should have had the same sign or zero.

Right?

Any ideas why?

I mention that these are reactions values of a basic seismic load case.

Thanks

Re: How to support a structure in only one direction

Artur.Kosakowski — Wed, 27 Feb 2013 10:11:20 GMT

Please check: http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Uplift-Elimination/m-p/3744231

Re: How to support a structure in only one direction

jo2ny — Wed, 27 Feb 2013 12:02:34 GMT

I read all the topics you indicated. Found out the explanation why dynamic modal analysis cannot be combinet with a non-linear structure. Therefore As a workaround I eliminated modal analysis, and the seismic load cases. I replaced the seismic loads with static horizontal loads (equivalent values) at the top of my 1 level structure. Now, without the modal cases I still get both + and - signed values in Uplift+ UZ supports. Actualy it seems that nothing is changed. Any ideas why? I did this test on a 2D simple frame , and it works as it should. I get one signed values, and zero. But my real model doesn't behave the same way and I don't know why.

Re: How to support a structure in only one direction

Artur.Kosakowski — Wed, 27 Feb 2013 12:07:22 GMT

I need the rtd file to look at.

Re: How to support a structure in only one direction

jo2ny — Wed, 27 Feb 2013 12:38:18 GMT

I attached the model.

Thanks for helping.

Re: How to support a structure in only one direction

Artur.Kosakowski — Wed, 27 Feb 2013 13:22:29 GMT

The analysis for cases 6,7 and 10 is divergent so the results are incorrect. Try to create combinations of these load cases with the vertical (stabilizing) ones as exists in reality and check the values of reactions again.

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.

Re: How to support a structure in only one direction

jo2ny — Wed, 27 Feb 2013 13:29:49 GMT

Ok, you're saying that if the combinations I will create (using the load cases you mentioned) will be convergent, then I can count on the results as being correct?

Re: How to support a structure in only one direction

Artur.Kosakowski — Wed, 27 Feb 2013 13:33:31 GMT

Yes, this is what I mean. In real life there is no wind without e.g. selfweight isn'it?