I have been given the task of designing a spreader bar to lift 16 tons. It's to be 12' long and no taller than 3'. We are looking at doing a triangle shape with one center hole at the top and holes on the bottom 1' apart to have adjustable widths for lifting. Could someone help me get started? We are looking for a safety factor of 4:1.
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Spreader Bar design
- Thread starter shears
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ok, assume your load is 64 tons (there's your SF = 4)
the worst geometry is when the base is the widest (why?)
assume you have the load applied where the spreader diagonal members attach to the spreader bar, 32 tons both sides (you need the CG of the load under the suspension point, justifying an equal load distribution). so you know the vertical component of the load in the diagonal member, and the angle, so you can calculate the tension load in the diagonal member, and size it.
you can also calculate the compression load in the spreader bar (the horizontal component of the diagonal load). You can calculate the euler load (of rather the section needed to carry this as an euler column) ... remember the speader bar can buckle about either axis.
If the load is going to be suspended from the spreader bar between the ends of the diagonal (rather than at the ends) this will complicate things ... the spreader bar becomes a beam column.
how will you adjust the length of the diagonal members to suit to different width on the spreader bar ? 12' long and 3' high means diagonal members 6.7' long, 10' (1' less at both ends) and 3' high means 5.8' long diagonals (using the 6.7' length for the diagonal means a height of 4.5')
the worst geometry is when the base is the widest (why?)
assume you have the load applied where the spreader diagonal members attach to the spreader bar, 32 tons both sides (you need the CG of the load under the suspension point, justifying an equal load distribution). so you know the vertical component of the load in the diagonal member, and the angle, so you can calculate the tension load in the diagonal member, and size it.
you can also calculate the compression load in the spreader bar (the horizontal component of the diagonal load). You can calculate the euler load (of rather the section needed to carry this as an euler column) ... remember the speader bar can buckle about either axis.
If the load is going to be suspended from the spreader bar between the ends of the diagonal (rather than at the ends) this will complicate things ... the spreader bar becomes a beam column.
how will you adjust the length of the diagonal members to suit to different width on the spreader bar ? 12' long and 3' high means diagonal members 6.7' long, 10' (1' less at both ends) and 3' high means 5.8' long diagonals (using the 6.7' length for the diagonal means a height of 4.5')
shears, I occasionally need to design some lifting equipment for my plant and decided, just to put things on a sound basis, to purchase ASME BTH-1 "Design of Below the Hook Lifting Devices". Haven't used it yet, but looks to be very helpful. About 60 USD as I recall.
Regards,
Mike
Regards,
Mike
Try these guys: (probably cheaper than do-it-yourself & test)
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