Finding forces in a wall of a trailer box filled with mass
Finding forces in a wall of a trailer box filled with mass
(OP)
Trying to calculate the forces against the wall of a trailer and not sure how to do that in the case of it being filled with grain. Any help would be appreciated. I know the weight and volume and the wall profile just not sure how to find the force acting straight out against the wall. The grain is just piled in there and the trailer is open.
Thanks for the help in advance,
-Jason
Thanks for the help in advance,
-Jason





RE: Finding forces in a wall of a trailer box filled with mass
RE: Finding forces in a wall of a trailer box filled with mass
Thanks
RE: Finding forces in a wall of a trailer box filled with mass
I suspect that the angle of repose is involved in the solution.
RE: Finding forces in a wall of a trailer box filled with mass
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Finding forces in a wall of a trailer box filled with mass
If it doesn't have suspension then half a g is a low estimate.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Finding forces in a wall of a trailer box filled with mass
Hydrostatic assumption is conservative, but angle of repose is not apparently involved.
Slides 40 to 50 of this very nice power point presentation:
www
RE: Finding forces in a wall of a trailer box filled with mass
Okay well I treated it like water and ended up a saftey of 15 so I guess its over built. This is what I did you guys can tell me if Im off the track a little:
1) Treated the grain like water using rho * g *h where h is the height of the trailer
2) after finding the force for the grain that would be used I applied a non-uniform sloped load over a flat surface and did bending-moment diagrams.
3) from the moment diagrams found the location that would be under the greatest stress
4) calculate my moment of inertia for the cross section at the point under the most stress
5) Used the M and the I to calculate the maximum pressure the wall should be exposed to.
6) Using that new force re-enter it into F = rho * g * h and calculate a new height and new volume of grain.
However would it not be better to use a FEA method since there is actually bending occuring along the height and the length of the trailer?
Thanks again
-Jason
RE: Finding forces in a wall of a trailer box filled with mass
Isn't the whole point of an internship to gain knowledge and experience under the tutelage and supervision of a mentor? Perhaps you need to speak with your internship program director.
Your approach seems ok up to step 4, if you are trying to look at the trailer as a whole. You seem to be treating the entire trailer as a beam. (I assume that your moment of inertia is for the cross section of the whole trailer?).
Things seem to fall apart in steps 5 and 6 however.
To use FEA you first must understand the problem, and the limits and capabilities of the program.
RE: Finding forces in a wall of a trailer box filled with mass
My intent wasnt to model the trailer as a whole since I am just looking into changing the side walls at this time. The front and back walls of the trailer are solid and would not be a problem.
As for the moment of inertia that I calculated it was for the length of one wall. Which bothers me because the wall is supported at each end (front and back).
When doing the bending moment diagram I also assumed it was the classic example of a pin on one side a roller on the other. Im not sure this was a correct assumption either.
RE: Finding forces in a wall of a trailer box filled with mass
This seems like a non-trivial problem, and one that is well outside my area of expertise.
RE: Finding forces in a wall of a trailer box filled with mass
FEA would be fine but an uncorrelated FEA model is of limited use. I'd be fairly sure of getting it right (having been involved with FEA for 25 years off and on), but would still do handcalcs of simpler load cases to back it up.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Finding forces in a wall of a trailer box filled with mass
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Finding forces in a wall of a trailer box filled with mass
http:
The subject of pressures in bins, hoppers and silo's has generated a lot of PhD's for a lot of people!
RE: Finding forces in a wall of a trailer box filled with mass
Are you modifying the design of the side walls or just doing a quick check to see if the current design will handle the loads?
ZCP
www.phoenix-engineer.com
RE: Finding forces in a wall of a trailer box filled with mass
I have never heard of, or dont recall hearing of plastic deformation theory but I will look into it. I was hoping I would use this problem as an excuse to force my employer into getting us a FEA program but I have limited to no experience with it outside using SOLID WORKS.
To answer zcp, yes I am modifying the wall and have a few designs in mind. We are basically doubling the length of the wall and playing around with supports other then a simple beam that separates two sheets. My calculations though were for a worst case unsupported wall so that we could have a base line to work from.
RE: Finding forces in a wall of a trailer box filled with mass
RE: Finding forces in a wall of a trailer box filled with mass
Available from htt
RE: Finding forces in a wall of a trailer box filled with mass
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However, the horizontal channles add very little strength in the plane that I am looking at.
RE: Finding forces in a wall of a trailer box filled with mass
If I can, I'll try to check if this very rough estimate comes anywhere near the plate maximum stress, with the two ends of the wall simply supported, the bottom edge of the wall clamped, and assuming you have three simply-supported cross members. Or is that one cross member?
RE: Finding forces in a wall of a trailer box filled with mass
However, I found that the maximum stress occurs at the midpoint of the bottom edge of the wall, which (in my example problem) turned out to be sigma1 = 0.0830*(1-mu)*rho*a*(h^3)/(t^2).
(Note that both of these results are fairly specific to only the stated sheet thickness, t = 2.657 mm, and probably wouldn't extrapolate to greatly different values of sheet thickness.)
Even though (1-mu)*rho could be refined to obtain a more accurate pressure distribution, what we can get out of this is, the maximum stress occurs at the midpoint of the bottom edge and can be fairly high because it's just a thin sheet there, in the vertical direction, under a relatively high bending moment about the bottom edge.
RE: Finding forces in a wall of a trailer box filled with mass
(As mentioned before, these results are fairly specific to only the stated sheet thickness, t = 2.657 mm.)