Trying to calculate the max deflection

[indebted]

I have a rectangular thin steel plate fixed on the two short ends with a rectangular cutout centered along one of the long sided. So it’s really a U-shaped plate fixed on the two sides with a uniformly applied force along the three inside edges a short distance in. To calculate the maximum defection, should I split this into three brackets or is there a better way?

 

[indebted]

This plate will suspend a slide-in module in the center of a cabinet unit.

 

[bvanhiel]

I think considering it as 3 brackets would be the most conservative. Adding a gusset at the front edges of your U to the sidewalls would probably help immensly.

-b

 

[corus]

I'd use a FE program for this kind of problem. If I really had to do it by hand then maybe I'd consider the plate edge-ways on and think of it as two beams. One beam would have the structural properties of the two plates that form the legs of the U with a uniform load applied along its length, and a second beam with a point load at its connection with the 'legs'. Generally a messy problem that is likely to lead to errors. Use FE.

corus

 

[GBor]

indebted,

Do you mean that it is fixed on either end? Or is this "track" bolted to the casing on one side? I'm a little unclear, but I'm picturing an electronics module being slid in to a control cabinet.

If it is fixed on either end and the module is being slid in, I think you may have two problems, not one. The first would be a simple beam calculation where you would calculate the beam properties and use a formula out of Roark's. You may even be able to look up a channel that closely approximates your channel, but that would take away the fun of calculating. For the load, I would use the weight of the module divided by the total length of beam supporting the module.

The second problem is making sure that the sides of the "U" don't bend excessively under the pressure exerted by the module. For this, I might go to FEA, particularly if there are any cut-outs.

If I'm misinterpreting, then sorry for the long-windedness...

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group

 

[indebted]

Thanks gents,

bvanhiel, That is very true. I do have a flange lip along what I would call the bottom of the U and an angled front flange to assist with alignment of the mating module.

Corus, I do have the pro/e of the support plate and will be learning Ansys sometime in the near future, so this might be the time to jump in and get my feet wet. With the angle slide in guides along the entry edges, this does seem to be a difficult problem to solve. I just wanted to make sure I wasn’t missing anything obvious.
I have changed jobs going from pure design to more of an analytical/design position, so I’m trying to get back into the mechanics of solids again. Roark’s and Practical Stress Analysis in Engineering Design (Blake) have been very helpful.

GBor, I think you have the layout correct. Hopefully the crude detail below comes out. The support plate is mounted just below a cabinet top plate (attached to the side walls) creating slide-in support for three flanges on a module, with the front flange stopping the unit.

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\|/ \|\
^
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[indebted]

Nope, the detail didn't come out correctly. The right leg should be shifted over two spaces to the right...

 

[bvanhiel]

I was referring to bending the flange out-of-plane at the front of the U to add stiffness. Are all 3 sides of the U fixed to the wall, or merely supported?

-b

 

[indebted]

bvanhiel, Good idea, I have front (90 deg)and rear (angled) flages on the bottom wall and side flanges with sheet metal screws to attach the bracket to the side walls. The bracket is only attached to the left and right side walls.

Side view
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|__o____\_______________o________________o__\

 

[bvanhiel]

I would try to put as much material out of plane gusseting the front that I could get away with, as that is where you'll get your stiffness on the short sides of the U. FEA is the only way to get an accurate answer. The conservative answer would come from considering each element separately.

-b

 

[indebted]

Thank you guys for all your insight.

I