Its not working....arrrgggg....I did compress it to .rar file, attached it and when I click on "post" the attachment dissapears and no post sent. Any Idea what might be the problem?
Sorry but I still cant send the file. Maby its the security insallation on my computer. I will send my model tomorrow.
But despite of me not being able to send the model, my instict tellls me that modelling the cables instead of manipulatin the supports is the right thing to do. Why?? because it will take a long time predicing how to define the supports. How can you place a support in these corners knowing how they will react in reality?????
Do you need to modell the cabels? Editing a support dos'nt take much time. adding a support in each corner with only Ux checked i think is the right way.
As I understand this problem, due to angle that the cables will form from the support to senter of gravity there will be axial forces acting on the frames. Applying a support that only Ux checked you wont be taking these forces into the calculations. And you get warning of unstable constuction.....
So there for I think modelling the cables gives you the correct picture of how this modell will react.
I have made a test model and tried to iterate the position of the support till the moment the values of bending moments is small enough to be neglected. Basically I started with step a and then I adjusted the support position moving it according to the values obtained from the reactions:
x movement = MY / FZ
y movement = MX/ FZ
You may want to exclude rods from self-weight loads.
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Here is a similar lifting problem, but with 2 levels of slings.
Check it out and comment it if you like.
The above suggested approach was used: moved the top support (pinned), then calculation, again moving, again calculation and so on, until minimum dispacements found.
On the base there are 2 UX and 2 UY blocked.
The load case intended for verification is DWNet.
DWLift is DWNet x 2
The other load cases don't quite work, because the loads they apply move the center of gravity somewhere else.
So it would be another equilibrium geometry for each of them.
How close to reality do you consider this model to be?
Download if from here http://www.fileshare.ro/e29427221