How to support a structure in only one direction

[saaddk]

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

[tony.ridley · Accepted solution]

[ghecks]

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.

[tony.ridley]

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.

[ghecks]

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.

[ghecks]

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

cheers

[AlexDT]

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 

[Artur.Kosakowski]

Alex,

What was the exact issue with your model?

[AlexDT]

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.

[Artur.Kosakowski]

Yes, it does.

[saaddk]

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

[Artur.Kosakowski · Accepted solution]

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.

[jo2ny]

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

[Artur.Kosakowski]

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

[jo2ny]

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.

[Artur.Kosakowski]

I need the rtd file to look at.

[jo2ny]

I attached the model.

Thanks for helping.

[Artur.Kosakowski]

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.

[jo2ny]

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?

[Artur.Kosakowski]

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