Crane Load Problem: Understanding Tension Torque and Beam Bending

[MotoPayton]

Can someone explain to me why the torque due to tension is taking from the roller instead of at the end of the beam.

If you were to take it from the end of the beam you would also need to take the torque created by the bending of the cable. This is obviously more complicated.

It just doesn't seem like the way they did it should work.

 

[NascentOxygen]

I can't figure out what is at B. Is the cable attached at C and slides over (above) a peg at B? Or is the cable attached at B, and a separate line connects B to C?

I think the cable might be fixed to the wall at A, and connected by a tensioned cable of fixed length to B. There is a separate lifting cable running from B to C that can be reeled in by a motor at B. That seems how it is analyzed, anyway.

 

[MotoPayton]

It is the same cable and that is a roller at B.

 

[NascentOxygen]

Then it looks like the extra force acting on the beam is a not-quite-vertical force at B, its line of action being midway through angle ABC. But I'm no expert.

Are there online resources where you can analyse beams and forces, as a check?