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Ceneter of Gravity

Ceneter of Gravity

Ceneter of Gravity

(OP)
I don't have anymore information than what is attached about the truck
My center of gravity knowledge is a bit rusty
Anybody can tell me the raised location of combined CG ?

The loads shown are Truck + Material in bed

Struggling to find raised combined (truck + material) CG in height and length

Thank you so much

RE: Ceneter of Gravity

I think you would have to know the empty and full weight of the truck and bed to determine this.

RE: Ceneter of Gravity

Weighted average could be used to solve for the CG in either case.

Hcg = [(Hm1 * M1) + (Hm2 * M2)] / (M1+M2)

So yes you need the mass of the truck, and the bed, and the product to be stored in the bed.
Break the regions into two separate masses(M) and find the heights of their respective CGs (Hm).

From XR250's post probably worth considering a few cases to find the location of CG that controls for your need.
You can apply the same procedure in any direction about any datum to find the location of the CG horizontally as well.

So you could first find the Xcg of the truck based on the axle loads. Then assume a height of the truck cg. Assume a height of the CG for the bed raised and then weight the averages.


RE: Ceneter of Gravity

(OP)
Dear driftLimiter (Structural),

The Empty weight = 44,000#
Material Weigth = 98,000#
Total Weigth = 142,000#

I am sorry it has been long time since school and havent came across with CG calculations
What are Hm1

Have any sample calcs or something that I follow
I appreciate your help

I dont have the truck itself (empty) CG and we dont know the truck that why I said this is all info I have
Any way that I can get the raised combined CG? or it is dead end

Thanks

RE: Ceneter of Gravity

Hm1 is the height of m1.

have you googled "center of gravity" ? did that, the equations, make sense ?

have you opened a 1st year engineering text ... just 'cause it's years since, doesn't mean you can't learn stuff for yourself.

yes, i'm feeling particularly crabby today.

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

RE: Ceneter of Gravity

Did you know there is a condition after partial unloading that is more unstable than when the load is first lifted?

RE: Ceneter of Gravity

(OP)
BUGGAR (Structural)
No I did not know about it
What condition is that? Could you please explain more in detail? Any article papers, pics, information will be tremendous help.

I greatly appreciate it

RE: Ceneter of Gravity

Quote (STRP88)

I don't have anymore information than what is attached about the truck
My center of gravity knowledge is a bit rusty
Anybody can tell me the raised location of combined CG ?

The loads shown are Truck + Material in bed

Struggling to find raised combined (truck + material) CG in height and length

This is why I took the time to learn concepts in school rather than equations. It is hard to forget concepts but easy to forget equations. As long as you understand the concept you should be able to derive the equations (in most cases anyhow). Made taking tests alot easier.

For center of gravity, you are taking the mass of an object and multiplying it by its moment arm about your datum (in your case - the ground). You do that for each object, add them together and then divide by the total mass.

RE: Ceneter of Gravity

(OP)
BUGGAR (Structural),
Can u please explain this condition you stated, "... there is a condition after partial unloading that is more unstable." ?

I really need to be careful with this and any information will be appropriated.

Partially full? how much is partially full?
Any papers or research on that, that you can reference please.


Also driftLimiter (Structural),
Based on all data that so far I have given I think I am unable to calculate the combined CG at raised position and I think without the CG of the truck empty I cant find the raised full material + truck combined CG, am I right?

Thank you

RE: Ceneter of Gravity

Go to YouTube and watch some videos of dump trucks dumping. I highly doubt there are research papers that would be useful.

RE: Ceneter of Gravity

The reactions at the wheels only tell half the story, that is, it is giving you the horizontal center of gravity. You need the other bit, that is, the vertical center of gravity, as that is what is rotating in both the horizontal and vertical directions.

To analyze this properly, you would want to know the horizontal center of gravity for the cab, and its frame (Mass 1). But you will need to know both the horizontal and vertical CG of the bed (Mass 2) which will be highly dependent of the contents of the load it is carrying. The CG of the bed should be centered in the horizontal direction (assuming load is distributed equally) but as you rotate up obviously the contents shift toward the rear as it begins to dump (and so does the CG)

I have not analyzed dump truck loads so I am not sure how manufacturers present their technical data.

RE: Ceneter of Gravity

StrP88,

Do you know the current centre of gravity? Do you know the centre of mass of the bed? If you don't, this is all a waste of time. If you do, you should be able to subtract the bed, and add it in again in its lifted state, doing the moments suggested by XR250.

Is anybody going to be checking your work? This looks to be safety related.

Nice fountain pen!

--
JHG

RE: Ceneter of Gravity

Yes I can explain but I think Wallach's idea of watching videos will tell you. I wouldn't have believed it but I seen it myself. We had the same problem dumping mine spoil cars.

RE: Ceneter of Gravity

Buggar it is actually quite intuitive. As you begin to unload, your load should be relatively centered in the bed. The CG of this load is very clearly in between your tires, ie no tipping. As you partially unload, the contents have shifted to the rear, moving your overall CG towards the rear, depending on contents, you may actually shift the overall CG behind the rear tires ie tipping.

RE: Ceneter of Gravity

Actually, the effect Buggar is talking about is a portion of the load sliding out, leaving a plug of material at the front of the trailer. This moves the CoG up and potentially to the side. It's probably only a problem on end-dump trailers like the OP illustrated on non flat terrain.

RE: Ceneter of Gravity

@ StrP88

I do think that you needed some more information, particularly the height of the cg of the truck.
Although it wouldn't be un-reasonable to assume the height in my opinion.

The info you provided you would need to make several assumptions about the vertical height of the mass cgs.

RE: Ceneter of Gravity

(OP)
BUGGAR (Structural),
Yes please explain it the videos do not point the problem as structural engineering point of view.
I watched them.
Please any photo, sketches ,explanation, studies

Have u guys designed truck-anti tip frame?
I am in need on some design hints, load cases , etc

Thank you

RE: Ceneter of Gravity

As indicated in another thread (Was it yours?) there is no cost effective option for a anti-tipping frame. The most cost-effective option is proper grade prep at the dumping location.

From a structural point of view, you NEED the centre of gravity of the empty truck to perform any useful calcs. Even a good rough estimate would likely suffice. Then you need to check it for some different loading cases as indicated above.

RE: Ceneter of Gravity

https://www.youtube.com/watch?v=kdoVTtbdugQ

This shows the trailer tipping over because the material at the bottom flows out before the material at the top even starts to move. Weight down low adds stability while weight at the top reduces it. Tipping occurs when the center of gravity goes beyond the the wheels. Having a suspension which tilts as the center of gravity moves to one side greatly decreases stability.

If the dump load moves as one solid mass the CG will always move down during the dump. If the lower material moves first the center of gravity will move up as material is dumped.

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