lifting the construction

[Anonymous]

How can i simulate that the construction is getting lifted in robot. The construction i have build is going to be lifted onto an oil rig. how do i simulate this in robot?

[Artur.Kosakowski]

I'm not able to download the file from this location.

Try to use either of these: http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Sending-bigger-files/td-p/3795062

[jo2ny]

Try here https://www.yousendit.com/download/UVJqTGt4ZEs5RmE5TE5Vag

[Artur.Kosakowski]

I think your approach is similar yet I personally feel that the fixed support one allows for easier adjustment of the position of the 'hook'.

I 'decided' to move it using the MX/FZ formula

BTW: I'm not sure if you can assume that you have fixed connections among the 'lifting' elements themselves as well as between them and the lifted 'box'.

[jo2ny]

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I 'decided' to move it using the MX/FZ formula

Yes, it;s better than my iterative method, theoretically you only need 2 simulations( one for determine Mx and Fz, and another one to verify the modified position)

BTW: I'm not sure if you can assume that you have fixed connections among the 'lifting' elements themselves as well as between them and the lifted 'box'.

Not having fixed connections between the lifting elements and themselves or others raises the need to introduce additional supports (or block more DOFs) in order to avoid instability, right?

What would you do to in this case? 

[Artur.Kosakowski]

What would you do to in this case? 

See the attached picture.

[Anonymous]

while giving elastic support with elastic coefficient 1N/m in X and Y direction, is it necessary to fix Rx and Ry directions or to asign any particular value for Rx and Ry??

Because when i do not fix Rx and Ry and not asign any value, the displacements are very very high or infinity??? what is the practical meaning of fixing these directions in elastic support?

thx for ur support,

Ajukul

[Anonymous]

Hi

I have a question regarding the lifting process using Robot. I modeled a steel module. I am going to simulate its lifting in the factory and also during installation process in the site. I defined a cable and added it into the model. I am going to analyze the stress, deflection and displacement produced on the module during lifting. Typically, during lifting an object, the object is subjected to its dead load. Also, I don't have information about the Section AX, and assembling parameters and its materials during defining a cable. I analyzed the module, but the deflection is wrong (too high in some nodes). Could u please check my Robot model attached here and give me some information for proper and accurate simulating of lifting process? Thank u so much

[Rafacascudo]

In this case, Don't model the cable as a "cable" element. It will only give you trouble.
Instead, model it as a truss bar (geometry/additional atributes). Additionally set the supports to fully fixed to avoid instabilities warnings

[Anonymous]

Thank u so much for your response

Could u please show me how to do it with truss bar on my module?

And if I want to use cable, how can I modify my attached file? What parameters should I change? Your helps will be appreciated in advance. Thank u

[Rafacascudo]

Cable element is used for large displacements analysis when loads are acting on its length like on a suspension bridge.

This is not your case.

As I said ,set your "cables" as truss bars here

Also , it seems you model came from Revit. It came with lots of bar releases ,which are giving lots of instabilities warnings that you cannot ignore ,and regular pinned supports at the botton that are not supposed to be there for a lifting analysis.

Also , the roof is a cladding with no loads applied on it . Your  "cables" have no bar properties assigned to them.

I suggest you correct your model 1st before thinking about the lifting part

[Anonymous]

Thank u so much for your guidance.

I modeled a building module in Robot at this time, and followed the steps you explained before. There is still a problem.

Execution problem No, 3060 occurs during analysis, and displacement and stress produced in members are too big which are wrong.

I don't know what should I do? Could u please check my model and help me? I attached my robot file here. Thanx

[Rafacascudo]

I tried lots of ways of modelling this .I Think The best one was

 1- setting a fixed support at your lifting point and using "truss" bars connecting to the 4 vertical poles at module´s top corners.

 2- Also the lifting point needs to be at center of gravity instead of geometrical center.

 3 - I also set 4 Ux,Uy elastic supports at modules bottom corners. They have a very very soft spring just to get rid of the instabilities. They generate neglegible reactions

 4 - And also changed the type of analysis to " Pdelta ,large displacements" which I think gives more reliable displacements

Model attached

[Anonymous]

Thank you so much for your help. Now it seems logical and correct. I will let you if I have any question later. Thanx again

[Anonymous]

Dear Rafacascudo 

After I analyzed the corrected module, It seems that the max displacement in the module is too big (88.5 mm). But the max deflection is around 28mm. I attached the deformation animation in this post.

Is it strange or not? Thanx

[Rafacascudo]

It depends a lot on the "cable" and vertical poles bars stiffness . Increase their sections and the displacements will get smaller.
Anyway 88mm and 28mm seems good to me

[Anonymous]

Thank u so much for your quick response

[Anonymous]

Dear Rafacascudo 

In your opinion, how can we optimize the module lifting process? 

For example should we consider different lifting configuration and compare some parameters such as max deformation, max displacement or max stress of the module element? In SAP 2000 I know how to inspect strength/stability of structural members according to the specified code, but I don't know how to do it in Robot. I goggled it but didn't find anything.

Can we model the connections between the module elements (studs to joists, etc.) and then see the lifting impacts on them? 

In fact, I want to optimize the lifting process by considering and comparing different lifting options and doing risk analysis but I don't know how to start it. I will appreciate your guidance and information in advance. Thanks

[Rafacascudo]

Robot has lots of codes that you can use to check your module bars and connections . Choose one of them on Tools / job preferences / codes.
Then , the best you can you is watch Robot official webinars on youtube channel. There is one exclusively about steel design. You can find the link to these webinars on the fixed threads above.
For the best lifting scheme, your module seems pretty standard . So I would go for a basic setup. I am no lifting expert but I think there are not so many lifting options for your module type.

[Anonymous]

Thank u so much. Regarding lifting process, as I said I am investigating and comparing different options. I simulated lifting the same module from cross beam and also from secondary frame. But the displacements are tool large. I attached their robot files. Could u please check my models? Are these models correct or I have to do some modifications on them? Thank you

[Rafacascudo]

The new 2 schemes on the new models have instabilities that are generating these huge displacements on one model and preventing convergence on the other.
These instabilities cannot be ignored. I am on cell phone right now. Try setting new weak horizontal springs on the cross beam and frame levels.
I'll have a look later