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Beam Flange Deflection under Eccentric Loading

Beam Flange Deflection under Eccentric Loading

Beam Flange Deflection under Eccentric Loading

(OP)
Hi all,

I've been asked a tricky question I'd like a couple of second opinions on before I answer regarding a beam loading case.

A heavy item of equipment in a box frame is seated on beams which run along its two opposite sides, but the beams will be set out wider than the box frame such that the load will pass through the box frame and onto a point about two thirds of the flange width away from the web of the beams.

So I was thinking to treat the flange as a plate restrained where it meets the web of the beam and do a quick minor axis bending check on that plate but I'm reasonably sure the flange of a beam will be stronger than this simplification will result.

How would you approach this problem? Any clearer ideas, or would you all take the simplified approach I was thinking?

Looking forward to hearing people's opinions - like they say, ask ten engineers & get ten different solutions.

RE: Beam Flange Deflection under Eccentric Loading

That is essentially what I would do. Spread the load out over a reasonable width based on the load width. This neglects the boundary condition on two sides of the "plate." If you want a more accurate result, then you will need to look into deflections of plates with supports on 3 sides, or FEA.

Don't forget about global beam bending/deflection if you are interested in total deflection. There will also be torsion. This rotation will cause additional deflection on the tip of the flange.

RE: Beam Flange Deflection under Eccentric Loading

Plate bending of the flange is one part of the problem, but I suspect a bigger issue is the twisting of the beams. As you described it, the load is applied outside the flange, so it is unclear how the load is applied. A sketch would be helpful.

RE: Beam Flange Deflection under Eccentric Loading

Here's an article describing a method similar to what you've proposed: Link.

And an old CMAA sample calc for cranes: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Beam Flange Deflection under Eccentric Loading

The words "heavy equipment" make me wonder if this is rotating or vibrating machinery? Is this an industrial situation? I would just field weld stiffener plates under the flanges and be done with it. Or better yet, span two beams across the bearing points to also provide torsional resistance to the support beams (use the stiffeners as extended connection tabs).

Thaidavid

RE: Beam Flange Deflection under Eccentric Loading

I agree with the above post from thaidavid

Mike McCann, PE, SE (WA)


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