SF & BM in lifted body
SF & BM in lifted body
(OP)
Dear all,
Perhaps someone could confirm my thinking on how to approach this problem. I have two solid bodies (see below) 'A' and 'B' which are joined together at the interface 'x' via a bolted connection.
LIFT DIRECTION
^
^
|
|
slide bar->|____________|______________|
| |
| |
LIFT POINT LIFT POINT
|-------------------------------------|
| |
|----------x| |
| body A | body B |
| | |
|----------x| |
| |
|-------------------------------------|
(side elevation)
The bodies are lifted upwards at the lift points shown. The lifting will be by ropes in a "vertical" arrangement (the rope slings will be truly vertical and connected to a sliding bar arrangement - shown). I need to know the shear force and bending moment at the interface x. I have analysed this system as a simply supported beam with two UDLs (see below) to get the reactions, SF and BM out.
As a beam:
---UDL1---------------UDL2------------
^ ^
| |
| |
The only thing that worries me is that I don't think the interface x will see the high moments predicted by taking the arrangement as UDLs. My thinking is that some of the moment will also be taken out by the pivot on the slide bar arrangement. Any thoughts?
Cheers,
-- drej --
Perhaps someone could confirm my thinking on how to approach this problem. I have two solid bodies (see below) 'A' and 'B' which are joined together at the interface 'x' via a bolted connection.
LIFT DIRECTION
^
^
|
|
slide bar->|____________|______________|
| |
| |
LIFT POINT LIFT POINT
|-------------------------------------|
| |
|----------x| |
| body A | body B |
| | |
|----------x| |
| |
|-------------------------------------|
(side elevation)
The bodies are lifted upwards at the lift points shown. The lifting will be by ropes in a "vertical" arrangement (the rope slings will be truly vertical and connected to a sliding bar arrangement - shown). I need to know the shear force and bending moment at the interface x. I have analysed this system as a simply supported beam with two UDLs (see below) to get the reactions, SF and BM out.
As a beam:
---UDL1---------------UDL2------------
^ ^
| |
| |
The only thing that worries me is that I don't think the interface x will see the high moments predicted by taking the arrangement as UDLs. My thinking is that some of the moment will also be taken out by the pivot on the slide bar arrangement. Any thoughts?
Cheers,
-- drej --






RE: SF & BM in lifted body
RE: SF & BM in lifted body
Assuming that's not the case, and that the system somehow stays level, you'd just sum moments about the interface, taking Body A as a free body diagram, to find the forces at that point.
RE: SF & BM in lifted body
LIFT DIRECTION
^
^
|
|
slide bar->|__________<_|_>___________|
If this is the case, which is what I've assumed, then I assume from your comments that my simply supported beam model of the unit above is applicable, and that the sum of the moments and forces about the interface (to obtain SF/BM here) would be appropriate?
RE: SF & BM in lifted body
RE: SF & BM in lifted body
Based on your two sketches I would say that your original analysis (no load [or very little]) at the slide bar is correct.
The lifting is being done by ropes that can only act in tension. To produce a horizontal reaction at the slide bar you would need to develop a couple through the ropes which would require one of the ropes to carry a compressive force. Also there would need to be an additional horizontal reaction in the system to balance the reaction at the slide bar.
RE: SF & BM in lifted body
RE: SF & BM in lifted body
-- drej --