rotational lift calculation .. urgent

[fabermechanical]

Hello,

I am enclosing a steel structure which weighs around 30tonne . need to find out if the 2 highlighted corner structure can handle a rotational lift of the steel structure from horizontal to vertical. What method can I use to find out if those corner structures can withstand the load. normally padeyes are used but i just want to find out if in any critical cases, instead of padeyes can they use the corner structures highlighted for a 2 point rotational lift. Can I use FEA/ any methods/ hand calculation, if its FEA what sort of boundary conditions can I use and where? Any help would be much helpful

Regards

faber

 

[rb1957]

i'd've thought hand calcs would do for this. you've got the weight, the lift force (applied near your corners), and the ground reaction.

to calc the force applied, i guess you'd look at the work done by change in potential energy of the weight, and the distance the corner moves and this (i think) will give you the force required. now you can do a free body of the strucutre (at an angle) with the lift force applied, the weight, and the ground reaction. then it should be a "simple" analysis to find the internal reactions in the structure.

remember to apply whatever safety factors are required.

 

[BAretired]

I'm not sure what you mean by rotational lift. If you lift vertically, the force required is 15 Tonnes (7.5 T per corner). That force may be resolved into the vertical and horizontal members for any position of the structure.



BA

 

[fabermechanical]

Hi there,

Rotational lift is 90 deg from horizontal position to vertical. It just to make the sleeping structure to stand upright. I just want to find out if those corner structures as highlighted in the figure can withstand the load. It will be held only in 2 positions as the padeyes initially fixed have been removed.
thanks

 

[rb1957]

i think i'm getting "ESL confusion". i understand the lift, but are you attaching temporary eyes for the lifting straps ? (i thought your original question was "do i have too attach eyes ?", or "i don't want to (attach eyes), is it ok ?")

mind you no-one will say "yea" or "nay" based on your very simple sketch. what sort of detail structure is in the corner ? (full weld i suspect) what sort of load has the strcuture been designed for ? (much more than self weight, i suspect) if the strcuture was designed for lifting eyes, you'd've thought that the designer would have considered this case. if the designer knew that the strcuture was going to be assembled horizontally, and then erected, you'd've thought he'd've considered this.

is someone (structurally intelligent) querying the design, or is this "just" a box being ticked ?

part of my original post was you need to be concerned about more than the two corners with the eyes.

 

[BAretired]

The structure rests on the ground, uniformly loading the bottom beam. At the start of lifting, the reaction at each end will be 15 Tonnes. As the lift progresses, the center of gravity moves toward the right on the sketch.

When it is directly over the right hand bottom corner, the entire weight will be on the ground and the lifting force will be zero.

If the center of gravity moves to the right of the bottom corner, the structure will lurch to the right unless prevented by some external means. So you need to have cables attached to slowly ease the structure into a fully vertical position.

BA

 

[fabermechanical]

All, I appreciate your time. Well to be more clear, a pressure vessel is inside the structural frame and everything in total weighs 30 tonnes app. so 15 tonnes at each end as mentioned by BAretired. Initially there were 2 padeyes fixed on the frame for rotational lift (90 deg) but later in the years it was removed, so currently there is nothing to tilt it in the vertical position. A quick fix would be to tilt it using the top 2 corner blocks as padeyes ( 2 point lift using shackles, chains). But I want to find out if the corner blocks can withstand the load as its not designed for lifting purpose rather just as a fixture for the whole frame. In the picture eventhough the frame is simplified, the corner structure is exactly the same and detailed as such. So we will be putting a shackle in place to tilt it but before that I want to run a FEA analysis or a hand calculation to confirm. I can isolate the corner structure alone, applying equivalent of 15tonne force on 3 faces of the corner structure and fixing the top notch to find out if the structure can withstand the load. If you are about to do a FEA on this scenario how will you do it. Thanks again for your time

 

[MiketheEngineer]

There are all kinds of engineers looking for a job - HIRE one

 

[fabermechanical]

Mike, If I have the money I would certainly hire one, I am just a beginner in this field, hence i am posting in this forum. Thanks anyway

 

[BAretired]

A hand calculation should be fine. The forces can easily be determined for any angle of lift but you need to know the location of the c.g. of the load.

The worst case of load occurs in the two corners diagonally opposite the circled corners because they must sustain the full 30 tonnes when the c.g. is directly above them. As the c.g. moves beyond that point, the lift force starts to increase. It reaches 15 tonnes just before touchdown.

BA

 

[rb1957]

depends on how they lift it, no? with the diagonal corners aligned vertically the ground reaction is weight-lift load. if they applying 15 tons of lift force then the ground reaction is 15 tons.

BA has made a very good point ... make sure you have some "preventor" straps to slow the structure once the CG is right of the ground point; ie make sure you can slowly lower the structure.

and make sure you brace the ground point (that you're pivoting about), so that the whole thing doesn't slide to the right !

it sounds like the structure originally had eyes attached, but now it doesn't. how close are your shackles to where the eyes were ?

how did you get the structure lying down ? (i assume that some time recently it was vertical ?)