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Lateral impact on thin vertical beam

Lateral impact on thin vertical beam

Lateral impact on thin vertical beam

I have a steel structure designed to hold a certain payload. This structure rests on 4 thin tubes of steel for legs (Ø60 mm total diameter for 2.5 mm thickness).

The structure is well-designed for intended operation, i.e bearing the weight of the payload. But I'd like to simulate an accident scenario where a small vehicle drives into one of the legs while the structure is in operation. So the not only are the legs axially compressed by the payload but one of them takes a lateral load, which I suspect will be a lot more stressful since it's a thin tube.

I know that the shear stress is 2*V/A, V being the lateral force of the vehicle's impact and A = 2*pi*(inner radius)*thickness

I want to know the highest V possible to add and apply this force to my current FEA, so to isolate it I'm looking for the maximum shear stress that a 425 mm high, Ø60 mm, 2.5 mm thick steel beam can take before breaking.

Steel is S355, the vehicle is assumed not to crumple on itself as it collides with the beam.

RE: Lateral impact on thin vertical beam

That is rather tricky, to say the least. Establishing V is going to be the hardest bit. It sounds as though you could approximate the pole as a spring, so you could then use a work equation, 1/2*m*v^2=1/2k*x^2, up to the plastic limit for x.

Given the tube dimensions it won't fail in shear, it'll fail with some sort of plastic deformation of the tube, causing a hinge and then plastic buckling.


Greg Locock

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RE: Lateral impact on thin vertical beam

Why not do an analysis of the side loading separately in the FEM? Check buckling, strength, etc.

RE: Lateral impact on thin vertical beam

Take a piece of tube, put some dead weight on it and ram it with a forklift? Fast, cheap, and simple.

RE: Lateral impact on thin vertical beam

Are the legs secured to the floor?
Sounds like you expect the legs to take the hit.

Hit 'em high, the attachment of one to 4 legs at the upper platform frame will be subjected to severe bending loads.
Hit 'em low, the attachment of one to 4 legs at the upper platform frame will be subjected to severe bending loads. Or the floor attachments (if any) will be tested at the closest leg.

Hit 'em toward the middle, like Greg said.

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