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RoryLarkin RoryLarkin
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3 years ago

I am interested in understanding the equilibrium of a beam suspended by two, three and four cables from the ceiling. The beam weighs a uniform 300 lbs and is 30 feet long  and the cables are 30 feet apart for #1 & #4 and equidistant for #2 & #3 . I believe I need to determine the angle of the cables first to determine the tensions. However I am not certain how the beam will alter its X axis (horizontal) position as the angle is increased from 0 deg (horizontal) to 60 deg using the cables to vary the angle. Initially at smaller angles I believe the beam will "self-center" where the two end cables will reflect approximately the same angles, only inverted. However, as the beam angle is increased I believe the beam will shift towards the shorter cable side. Somewhat obvious is in order to change the angle of the beam the lengths of the cables will need to be computed based on the equilibrium in order to balance the load of the beam correctly across all cables - when more than two cables are used.
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Valued Member
Educator
3 years ago
Hi Rory,

For a problem like this, all the forces along the y-axis must sum to zero, and all forces along the x must do the same. We'd need to know more information about the wire, such as their angles. You may need to consider moment at each point? What other information have you been provided?
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RoryLarkin Author
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3 years ago
Hello bio_man,

I agree with your comments on the sum of the forces / moments. There is no other information "known". This is where I find myself in a small circular pattern.
1) I need to be able to determine where the beam - with the present uniform distribution of 300 lb - will "normalize" to (settled POSE) for a case of just two cables (for simplicity).
2) for smaller angles - ie +/- 30 deg - I believe the cables will self center where their respective angles are the same but mirrored. This can be determined with the length of cable #1 (left) and cable #4 (right). Obtain the difference, apply LOS & LOC to determine the angles.
3) For larger beam angles - where the longer cable will carry less of the tension and the shorter cable tension will increase - the beam will find it's equilibrium closer to the short cable.
4) Angle and height of the beam dictate an approximate cable length in which to produce the POSE. However the "settled" angle of the cables - where the beam finds its equilibrium will be one unknown required to compute the tension / load distribution required to compute the final angle of the cables.
wrote...
Valued Member
Educator
3 years ago
Hi RoryLarkin

Sorry for replying so late. This is a difficult question, at lead for me as I'm not into engineering physics. However, I may be able to help -- notice my attachment.

I actually found a question similar to yours, but with more information provided. Maybe it'll help you understand how to do yours.

Sorry I couldn't be of more help to you!
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