Hello,
I am modeling a structure that will consist of an I-Beam with a post at its center and two cables that span from the ends of the I-Beam to the end of the center post (creating a triangle).

I was originally going to add a standard force to each mounting surface of the cables, but that would put the cables in compression. Also, if I don't model the cables themselves (just add forces where the cables mount) then I won't get an increasing force as the "cables" are stretched during loading.

Any advice would be greatly appreciated.

How do you put a cable in compression? Isn't that like trying to push a rope?
I think more information is needed.
I would load the assembly the same way it will be loaded in the real world.

You can model two scenarios. In the first the cables are under tension. In effect they are just thin rods.

If your loading changes and they go into compression then you need to delete them from the model.

IF your program is suffciently clever you can get the same effect by replacing each cable with a pair of rods connected by 3 hinges. This will collapse under compression but work under tension.

The stiffness of a cable is much less than that of the same diameter rod, you need to account for that.

If your cables are pretensioned then things are more complicated.

Cheers

Greg Locock


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GregLocock, you pretty much nailed the problem and my thought processes. The problem is the cables are pretensioned. If they were un-tensioned cables, that would be easy (just draw rods of the correct diameter). The pretensioning of the cables is going to provide a significant structural influence by causing the beam to bend upwards against the main load. I would like those cables to have a 50,000 to 100,000 pound pretension but don't know how to apply it. The only way I know how to model tension is to apply opposing forces to each end of a cable, but I believe this will ACTUALLY model compression on the cables.

You could use a Spring Force in Dynamic Simulation.

Use linear superposition theory

Cheers

Greg Locock


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Analysis of cables is always done with cables in tension for reason explained above. Your sketch also lack where the I beam supports are to be located, so whatever you are trying to do is a little mystifying. More info is needed as requested above.