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Torsional Constant For A Ladder Chassis

Torsional Constant For A Ladder Chassis

Torsional Constant For A Ladder Chassis

Hey guys! I'm currently designing a ladder chassis for a vehicle design assignment. I'm having troubles finding the torsional constant, J of a ladder chassis which is needed to find the torsional stiffness.

The ladder chassis will consist of 2 side members and 3 cross-members spaced equally along its length.
All the members are C-sections.

Am I suppose to sum up all the area moment of inertias, e.g. J = 2*I(side member) + 3*I(crossmember)
Is this analysis only possible using a software?

RE: Torsional Constant For A Ladder Chassis

It's not going to be that simple, and it's going to depend on how the crossmembers are connected to the main beams. If they're tacked on with a couple of rivets, they're not going to do much. A proper solid (welded-all-around) connection will do more. It is certainly not going to be as simple as the total of all three.

RE: Torsional Constant For A Ladder Chassis

Wow that was a quick reply, thanks alot! Okay, lets assume that the connections are properly welded.
How about if I simplify the model by using a frame with only 2 cross-members located at both ends (essentially making it a square when viewed from top). Is it possible to find the torsional stiffness by hand now?

RE: Torsional Constant For A Ladder Chassis

C sections/channels like andy "open' section will have mighty low torsional stiffness.
C and I sections are used when Low torsional stiffness is sometimes desirable.

Omer Blodgett says open section lateral Crossmembers don't add much.


More detailed info in Lincoln Electric's bargain Design of Weldments.

As I recall simply "boxing" the channels increased torsional stiffness

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