standard way to apply the force of a human being standing on a plate?
standard way to apply the force of a human being standing on a plate?
(OP)
As the title says:
Is there any standard way to apply the force of a human being standing on a plate?
European standard EN280 says I should apply a point load, but a point load in FEA results in much too high stresses where the force is applied. How is this normally taken care of?
Is there any standard way to apply the force of a human being standing on a plate?
European standard EN280 says I should apply a point load, but a point load in FEA results in much too high stresses where the force is applied. How is this normally taken care of?
NX 7.5
Teamcenter 8





RE: standard way to apply the force of a human being standing on a plate?
else, you could apply the load over an area, say 2*50% footprint ?
RE: standard way to apply the force of a human being standing on a plate?
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RE: standard way to apply the force of a human being standing on a plate?
Imagine a 200 lbs "lady" hitting the floor in heels. Wouldn't each shoe would have 3x4 sq surface at the toe, plus maybe a 3/8 x 3/8 area on the heel? Worse case, the heel comes down with an impact load of perhaps 60% body mass on the hell (er, heel) as a single point load over that 3/8 x 3/8 surface.
The rest would be on the tow of the other foot.
Then again, figure my weight of 155 lbs over a 12 inch long safety-toes work shoe. 155lbs/2 shoes/(12x3 per shoe) ... But that isn't a point load either.
RE: standard way to apply the force of a human being standing on a plate?
I'll just work something out then I guess. Thanks anyway.
NX 7.5
Teamcenter 8
RE: standard way to apply the force of a human being standing on a plate?
Ignoring for a moment the issue of what is the smallest physical "point load" in the real world, the concentrated load distributes as it propagates down from surface of the slab to the mid-plane. Using the old rule of thumb of a 45 degree angle of spread, by the time the "point" load reaches the mid-plane of a slab of thickness D, it will have an effective "footprint" approximately diameter D (or a square D x D).
In general, I spread "point loads" over an area comparable to thickness of the plate / slab to "dissipate" concentrated point load effects. If you need to understand stresses at a scale comparable to or smaller than the plate / slab thickness, you need to be considering other modelling techniques, such as solid elements, and a "real" footprint for the applied load.
http://julianh72.blogspot.com
RE: standard way to apply the force of a human being standing on a plate?
Basically, all I want to know is: will my sheet metal plate (supported by square tubes) be able to support 3 people standing on it. Or, how far do I have to put the tubes apart so that the structure is as light as possible, yet still strong enough.
When I apply my 3 people as point loads, the stresses are noticeably bigger then when I, for example, make 3 circles with diameter 50mm (~2inch) and apply my forces there. The size of the circles has a direct impact of the maximum stress, which is logical.
Only problem is that I can't find any reliable source regarding the size of said imprint.
I feel like I'm terribly over-thinking this, and there should be an easy way to fix my problem.
Hoping you guys can help.
NX 7.5
Teamcenter 8
RE: standard way to apply the force of a human being standing on a plate?
RE: standard way to apply the force of a human being standing on a plate?
So your per-person "point" loads will be spread out over the area of each foot, then each of those will be about 1 foot apart.
Hint: 2 mm isn't thick enough.
RE: standard way to apply the force of a human being standing on a plate?
I'm currently looking to use 3,5mm alu treadplates, with a maximum span of about 40cm. with a distributed "foot-sized" load, this seems to be working fine. Point loads still give problems though.
NX 7.5
Teamcenter 8
RE: standard way to apply the force of a human being standing on a plate?
Tobalcane
"If you avoid failure, you also avoid success."
"Luck is where preparation meets opportunity"
RE: standard way to apply the force of a human being standing on a plate?
The standard is from 2009 but doesn't mention FEA. You're probably right about the force load. I was kind of thinking the same.
NX 7.5
Teamcenter 8
RE: standard way to apply the force of a human being standing on a plate?
Again, your particulr problem might be different, so I apologise if i missed the point.
RE: standard way to apply the force of a human being standing on a plate?
Dimensions in mm
The plate you see is supported on the bent flanged (the 25mm ones).
Assuming the 740mm length can't be changed, how wide(current length 511mm) can I make the sheet so that it allows a person to stand in the middle of the sheet (and/or 2 people standing 500mm apart) without deforming the plate.
As you see this isn't exactly a beam problem and I can't seem to find a simple way to solve this manually. Hence the FEA.
Now when I apply a point load in the center of the plate of 1kN (80kg+25%), the local stresses go up to over 200N/mm², where the treadplate only allows 50N/mm² (yield strength=80N/mm²+1,65 safety factor)
Even if I reduce the span of 511mm to 300mm it still gives too big numbers, and, while I may be wrong here, I find it hard to believe that a 3,5mm alu plate of those dimensions can't support this kind of force.
So here goes my question: How am I supposed to apply my load of "1 person" so that it would give me a result I can work with?
NX 7.5
Teamcenter 8
RE: standard way to apply the force of a human being standing on a plate?
Tobalcane
"If you avoid failure, you also avoid success."
"Luck is where preparation meets opportunity"
RE: standard way to apply the force of a human being standing on a plate?
You can find more accurate formulas in Pilkey, Tables 18.
Please take above numerical results with a big pinch of salt.
RE: standard way to apply the force of a human being standing on a plate?
The only question that hasn't been answered yet is if the 160x300mm² is a good definition for a human imprint.
NX 7.5
Teamcenter 8
RE: standard way to apply the force of a human being standing on a plate?
RE: standard way to apply the force of a human being standing on a plate?
Extrapolating to a 0 value for a1/b and b1/b would equal applying a point pressure, but I don't know if that would be necessary, as it severely increases the required strength of the plate. (2,75 times higher). That would mean I'd need a 7mm alu plate, which I find very hard to believe.
NX 7.5
Teamcenter 8
RE: standard way to apply the force of a human being standing on a plate?
In this case you can ignore the EN280 design standard methods of analysis and make what you consider are reasonable (but conservative) assumptions to reflect the real world situation in your model. Limit your FEA surface stresses to yield, and the mean stress through the thickness to 60% yield, and use some safety factor so that you are confident the design is safe even in the worst situation. In such a case then, I'd assume you have 3 people on tip-toe standing on one leg. The worst case could either be when they stand in the mioddle or at one edge (where buckling might occur).
RE: standard way to apply the force of a human being standing on a plate?