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Valued Contributor
mortel09
Posts: 56
Registered: ‎01-31-2012

Re: lifting the construction

04-24-2012 03:07 AM in reply to: Artur.Kosakowski

Iam not sure if its okei or not. You can look at the file that i attached earlier. 

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Artur.Kosakowski
Posts: 5,115
Registered: ‎12-17-2010

Re: lifting the construction

04-24-2012 03:24 AM in reply to: mortel09

I would say that something has to be corrected

 

displ and rot.PNG

 

 

 



Artur Kosakowski
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Valued Contributor
mortel09
Posts: 56
Registered: ‎01-31-2012

Re: lifting the construction

04-24-2012 04:12 AM in reply to: Artur.Kosakowski

yeah, I see it now. Whats your opinion of what i should do? If i added a Support in node 1 (RX, RY and RZ) i get as good as zero. Would this be the proper way of doing it?

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Valued Mentor
Rafacascudo
Posts: 367
Registered: ‎05-16-2011

Re: lifting the construction

04-24-2012 10:37 AM in reply to: mortel09
RX,RY and RZ support on node 1 will give significant MX and MY moment reactions on this support. Try putting very soft Ux and Uy springs, like 0.01kN/m on the 4 botton nodes of your model.This will eliminate the instabilities. This solution will be as good as you get closer to ZERO on these X,Y reactions. To achieve that ,your lifting point coordinates (node 71) should be as precise as the CG of the loads on your lifting load case/combination. The lifting case should match this criteria. model attached
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Member
thomoh08
Posts: 3
Registered: ‎04-25-2012

Re: lifting the construction

04-25-2012 01:32 AM in reply to: Rafacascudo

After we put the soft springs in each of the four corners we still get a wierd reading in the displacements bar under node properties. 

 

See attachment.

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Valued Contributor
mortel09
Posts: 56
Registered: ‎01-31-2012

Re: lifting the construction

04-25-2012 02:21 AM in reply to: thomoh08

I put the springs to 100 kN/m and got rid of the displacements, dont know if thats the best solution. The reactions in the springs is still very low..

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Valued Mentor
Rafacascudo
Posts: 367
Registered: ‎05-16-2011

Re: lifting the construction

04-25-2012 12:00 PM in reply to: mortel09

as I said before " your lifting point coordinates (node 71) should be as precise as the CG of the loads on your lifting load case/combination"

   This will not work with several load cases.For each load case you should have a unique lifting support type(UX + coordinates) according to the lifting point coordinates.

If the lifting point coordinates doesn´t match the Loads CG , the sum of the cables horizontal components will not be zero and as consequence you´ll get horizontal reactions on the XY supports and large displacements on the structure nodes

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Active Member
ingolfurj
Posts: 10
Registered: ‎05-02-2012

Re: lifting the construction

05-03-2012 12:42 PM in reply to: mortel09
Hei guys. Just read this thread and found him quite interesting. Now that the problem is probably solved my comment is perheps as useless as a ear on an elbow. But I will shoot anyway.
I just wonderd if modelling the cables, lifting the construction, would work but only modelling them half way to there meeting point ( center of gravity) or so and placing a support there for every cable. Then you would get 4 pin supports, and realistic force distribution in your structure with x, y and z forces acting on the corners....
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Valued Mentor
tony.ridley
Posts: 653
Registered: ‎09-07-2011

Re: lifting the construction

05-03-2012 04:06 PM in reply to: ingolfurj

hmmmmm my suggestion:

 

download Mortels' model from this thread and try!  Post the results.

 

Tony

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Active Member
ingolfurj
Posts: 10
Registered: ‎05-02-2012

Re: lifting the construction

05-04-2012 01:36 AM in reply to: tony.ridley

Hei!

Just downloaded the model and playd with it a little.  I did have to place fixed supports at the end og the cables, forcing them to get some moments but placed an release at the connection to the main struture so that the moments wont travel further into the structure.  I have not been using Robot for a long time so this may be total fail but this way I think the axial forces from the cables with there angle towards center of gravity will be taken into account without playing with supports at each corner

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