Special case in rectangular plate bending 1

[greycloud]

Greetings

I'm dealing with a case where a rectangular plate is subjected to a bending moment applied mid span of the plate along the shorter edge. I tried looking for a formula for this case but couldn't find any so hope you can help

 

[rb1957]

were we right ? how did your boss want you to solve it ?

Quando Omni Flunkus Moritati

 

[greycloud]

we got another job so i didnt show him my solution yet . he wanted me to get a bending equation for an unsupported rectangular plate with a moment applied mid span and then use the 2nd moment of area and centroid for the plate and supporting beams combined to get the stress.

 

[rb1957]

seems an odd way to solve it, IMHO

Quando Omni Flunkus Moritati

 

[BAretired]

we got another job so i didnt show him my solution yet . he wanted me to get a bending equation for an unsupported rectangular plate with a moment applied mid span and then use the 2nd moment of area and centroid for the plate and supporting beams combined to get the stress.

An unsupported rectangular plate with a moment applied mid span is not in equilibrium. Your first sketch in your Aug. 8 post showing a plate of length a and width b with a moment in the middle is not in equilibrium as pointed out by paddingtongreen the same day. If you and your boss don't know that, you both need to review elementary statics.

If that plate is simply supported along the short ends b, the reaction at each end is M/a and the moment at any point x from the one end is M.x/a - M(x>a/2) where (x>a/2) is a boolean function equal to 0 when x<a/2 and 1 when x>a/2. By inspection, the moment varies linearly from 0 at each end to M/2 at the middle. The moment per unit width varies from 0 to M/2b.

As rb indicated, it seems an odd way to solve it. I would go further and say it is not the way to solve it. Your boss should think it through once again.

BA

 

[greycloud]

BA: by unsapported i meant unstiffened plate, my boss has indeed strange ways to solve problems, he even sometimes uses the wrong equations and i got into an argument once with him over that.

 

[BAretired]

I still don't know what he means when he calls it an unstiffened plate. The plate is stiffened by ribs in the form of angles welded to the plate running the length of the ship.

I have no issue with treating it as a composite section where the section properties can be calculated using standard methods, but in order to solve the problem, boundary conditions are required. This means knowing how the plate is supported. I thought this had been resolved when you advised that it was supported at bulkheads acting more or less like bearing walls. If that is the case, the solution I suggested earlier is a reasonably good approximation of the behavior of the deck in resisting the action of the winch.

It's not clear to me what the objection is.

BA

 

[greycloud]

if you guys are still there

yesterday as i had some spare time i showed my boss the calculations using the method

you taught me here. he said that it is acceptable by him but he doubts its acceptable by the classification classes and that its not a good enough method. he is still insisting on his method and i honestly doubt that it's correct.

 

[rb1957]

i guess the problem with learning is you're not seeing the whole picture (i don't understand "classification classes") and maybe aren't explaining it well (ESL?).

if your boss is insisting on a particular analysis path, maybe it time to say "yes sir". the key thing with any analysis is to draw FBDs of where the load is going; if you can do that then your analysis isn't too "wrong". the next thing to consider is strain energy, and whether the analysis is using the lowest total strain energy to react the loads (lower is typically "righter").

it'd be interesting so see a sketch of how your boss thinks the loads are reacted.

another day in paradise, or is paradise one day closer ?

 

[BAretired]

Classification classes? What are they? If your boss has a method of solving the problem, how does the solution compare with the one suggested here? Can you demonstrate his method?

BA

 

[BAretired]

Classification classes? What are they? If your boss has a method of solving the problem, how does the solution compare with the one suggested here? Can you demonstrate his method?

BA

 

[rb1957]

looks like there's an echo on the line

another day in paradise, or is paradise one day closer ?

 

[BAretired]

Yeah, sorry about that.

BA

 

[dhengr]

I think we are just talking into an empty room with real bad acoustics, and only the echo is being heard and understood, and that, only by the original speakers. If the OP’er. can’t show us exactly what his boss wants, and the methods he wants used, we are wasting our breath. He must show how this barge is actually structured and how the winch is fixed to the barge deck, and he hasn’t really done that yet either.

 

[paddingtongreen]

I suspect that the boss wants him to find a plate that is the equivalent of the actual reinforced plate, and then apply the load on a very large or infinite section of it. Local effects would show up but the reactions would be small enough to disappear.



Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin