topic Re: lifting the construction in Robot Structural Analysis Forum

lifting the construction

Anonymous — Thu, 19 Apr 2012 11:16:31 GMT

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?

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 11:35:37 GMT

add pinned support at the lift point, remove usual supports. add self weight multiplied by a dynamic allowance for lifting.

thats it!

tony

Re: lifting the construction

Rafal.Gaweda — Thu, 19 Apr 2012 11:44:56 GMT

Kudos for you Tony 🙂

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 11:54:55 GMT

I have done that now, and I have connected the cable from the four corners to the pinned support. but when i calculate I get several warnings about instability in nodes and other warnings. How can I solve this problem? After the calculation the ratio is extremly high....

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 12:01:44 GMT

no sorry, I didnt mean add cables and then a single pinned support. I mean add 4 (or how many you need) pinned supports at the place WHERE THE CABLE IS GOING TO CONNECT. you don't really need to model the cable, no?

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 12:05:50 GMT

My construction is going to be lifted at 1 point, so i added a pinned support over center of gravity of the contruction and connected cables from it to the 4 corners... but that didnt work very well... so what you are saying is that i should add 4 supports over center of gravity and then i dont need to pull cables to the corners?
I dont need to calculate the wire no...

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 12:31:26 GMT

I would not add the support OVER the CG, rather add a support(s) to the BEAM itself at the point(s) where the cable will attach. Looking at the reactions at each support will tell you if the structure will be stable when it's lifted.

Adding a single support for a structure with no rotational restraint can't ever be modelled..

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 12:36:12 GMT

I have attached a pic of what I have done, is this what you mean I should do (supports.png)? I have also attached a pic of how the lift will look like in my mind (supports2.png). Will it calculate the same thing ?

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 13:00:09 GMT

Of course, the structure modelled in "supports2" can never work.

It can spin around the support with out ever stopping!

So no, it won't calculate the same thing.

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 13:23:38 GMT

okei, but if i had added a support that only takes forces from x and y directions in each corner at the bottom of the construction, and made sure that the reactions in the support is very low, so that the construction would not spin, would that be a possible solution? and make the support in top only takes forces in z-direction

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 13:09:58 GMT

Perfect! (well, most likely you will need a lateral support at at least 2 corners)

or spring supports..................

Re: lifting the construction

Rafacascudo — Thu, 19 Apr 2012 15:22:26 GMT

That´s not true.Forces on the inclined cables will produce horizontal forces on your structure. I would set the supports on the exact direction of the cables.Doing that you won´t need to add any other supports. For creating the " tricky" support ,create a new one fixing de X direction , then click on " direction" and give the coordinates of the point where the 4 cables will join.Then assign this support to your 4 lifting points.Check if they´re on the exact same direction of your cables.

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 15:47:32 GMT

Should all of the "fixed directions" be checked? Like on the pic?

Re: lifting the construction

Rafacascudo — Thu, 19 Apr 2012 16:47:08 GMT

No ,just Ux ,as long as you set the support local direction like I recommended

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 18:11:17 GMT

okei, but dose it look like i have done that according to the piecture i attached?

Re: lifting the construction

Rafacascudo — Thu, 19 Apr 2012 19:26:25 GMT

Yes ,but it looks like the support directions are wrong, probabbly due to the fact you assigned a fixed support for them all

Re: lifting the construction

Anonymous — Thu, 19 Apr 2012 22:44:16 GMT

Forces on the inclined cables will produce horizontal forces on your structure.

Perhaps this is true, but your method seems like a lot of hard work for not much gain. But each to their own

Re: lifting the construction

Anonymous — Fri, 20 Apr 2012 08:33:24 GMT

okei, ill try that 😉 thx

Re: lifting the construction

Rafal.Gaweda — Fri, 20 Apr 2012 10:06:10 GMT

Re: lifting the construction

Anonymous — Fri, 20 Apr 2012 10:22:42 GMT

so now iam suppose to check of UX, UY and UZ? and not only UX?