REACTIONS during lift 1

[fabermechanical]

Hi,

A question with REACTIONS. lifting application, a container is lifted using slings. Equivalent load for 23 tonnes is applied on the downward direction equally on the faces of the container. While placing these boundary conditions in the software, the software predicts REACTIONS at the hook in Newton. The reaction value predicted at the hook is 245 KN. Could someone please explain what that REACTIONS means and how can I determine the container structure is suitable for lift.

thanks
faber

 

[CANPRO]

See the 3rd law....

http://en.wikipedia.org/wiki/Newton's_laws_of_motion

 

[fabermechanical]

Thanks for your reply. for every action there is equal and opposite reaction. In my case, if the selfweight of the structure is 4 tonne for example, I am getting a reaction of 1 tonne from STAAD software. does it means my structure is sound enough ?

 

[rb1957]

"for every action there is equal and opposite reaction" ... correct

"if the selfweight of the structure is 4 tonne" = load

"a reaction of 1 tonne" = reaction, yes? if there're four of them then yes load = reaction, yes?

"does it means my structure is sound" ... no, the software will tell you the reactions, it probably doesn't know how strong the element is (unless STAAD allows you to input strength)
STAAD will tell you the load in an element, maybe 1kN. you need to assess whether the element can carry to load; typically you'll use load for things like straps and slings, which have an allowable load.
STAAD will also tell you the stress in an element, may 100MPa. you need to assess whether your structure can carry this stress ... material allowables, fty, and/or geometry allowables (crippling, buckling.

 

[paddingtongreen]

If you put the member sizes, materials and if STAAD knows the code it will give you a pass/fail as well as the stresses and more info than you will know what to do with.

I have a concern though, the result is only good if the slings are the same length, or if the load is flexible enough to adjust till the loads are equal. If the load was very stiff, such as a closed box, and one sling was longer than the others, it and the diagonally opposite one would see little of the load, the other two would carry most of it.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[fabermechanical]

Thank you guys for your valuable time by providing your valuable inputs. I was inputing a final value wrongly hence I was confused with the whole phenomenon. I need to practice this software a lot and read some fundamentals. Thanks again.

 

[dhengr]

Fabermech:
You should also take a look at Newton’s Law #37 which goes something like this... If you are going to claim to be a mechanical professional on a forum, and do these kinds of problems, you should probably own Statics and Strength of Materials text books which you have actually read and studied. Maybe even get some real engineering education on the subject before you hurt someone. It appears that you are in way over your head. A software program does not an engineer make. Doubly so, when you don’t understand the software you are trying to use.

In Newton’s day a software was a linen blouse rather than a suit of armor. What did they know? In those days they changed their softwares once a month whether they needed to or not. Today the software editions change faster than you can pay for them. But, his admonition still applies because he was concerned about falling objects like apples (or containers full of apples) falling on someone’s head, when an ill informed person tried doing things they had little education, understanding or experience to do. Please address these type questions to your boss so he knows what you know and what you don’t know. He can help keep you and the company out of trouble and keep you from hurting someone.