How to evaluate the resistance of a wire mesh by calcs ?
How to evaluate the resistance of a wire mesh by calcs ?
(OP)
Hi,
I have a client who asked me to evaluate how much pressure his steel cage can handle. It consists of HSS beams/columns with wire mesh. He asked me if it can "WITHSTAND A MAXIMUM IMPACT OF 295 psi"
My question is regarding the wire mesh, is it possible to calculate?
Its a cage where industrial tires will be inflated...
thx
Gasma1975
I have a client who asked me to evaluate how much pressure his steel cage can handle. It consists of HSS beams/columns with wire mesh. He asked me if it can "WITHSTAND A MAXIMUM IMPACT OF 295 psi"
My question is regarding the wire mesh, is it possible to calculate?
Its a cage where industrial tires will be inflated...
thx
Gasma1975






RE: How to evaluate the resistance of a wire mesh by calcs ?
RE: How to evaluate the resistance of a wire mesh by calcs ?
RE: How to evaluate the resistance of a wire mesh by calcs ?
What he means is "I want this to restrain a tire/rim combo that blows apart at 295 psi". The impact force of a split rim on the wire mesh could be a lot higher than that. The gas pressure would be a lot lower than that. The 295 psi comes from the requirement in 29 CFR 1910.177 about 1.5 times the maximum pressure, which is shown on the drawing as 195 psi or so.
I don't know that you can get a fool-proof approach to this without a lot of testing. You can come up with some estimate of the maximum speed of a wheel or a split rim or a wheel-tire combo if it blows apart, and design to absorb that much energy from the impact. If the cage fits close around the tire, you could possibly assume that the tire blew out against the cage on both sides and design for that static force as an additional load case. If a tire blows out (as opposed to blowing off the rim), the whole assembly could jump straight up or to either side. I would think that the customer would need to either pay for a bunch of testing, or accept some or all of the liability for the design of the cage. It would be prudent to look at commercially available cages, too. The successful use of the cage involves using it properly, and is not just a structural issue. (For example, have any part of your body inside that cage at the time, and it's liable to be missing, even if the cage "works".) If the rims or wheels are in current production, it might be worthwhile to try to see if those manufacturers have any recommendations on cage construction or use as well.
Note that tires of the same general physical size can vary considerably in weight based on construction and load rating. Note that wheel/rim parts can vary in weight as well (budd vs spoke, 1 pc/2pc rims, etc.)
I would consider grating or plate rather than expanded metal in the construction. If it's supposed to be portable, that could get tricky.
Long ago, I worked in a dump-truck company and did a lot of flat-fixing, and all the wheels were split rims. It is possible for these things to blow apart, and is a serious concern, but it's not something that happens twice a week either, so that makes it harder to have a good feel for the effects.
RE: How to evaluate the resistance of a wire mesh by calcs ?
Normally, the action of an inflated tire keeps the split rim in place, so you can't pop the rim off an inflated tire. And normally, the first thing we did when we brought a tire in was to remove the valve core. But one time, I neglected to do that and pried the split rim off a tire that had just a very little amount of pressure still in it. When it came off, the rim went about 5' in the air. I still have a scar about a 1/2" long on one finger from that. That wasn't enough pressure to pop the tube.
RE: How to evaluate the resistance of a wire mesh by calcs ?
I agree with your comments. They come from practical experience and engineering...usually the better combination.
Split rims are inherently dangerous. As I'm sure you know, people have been killed by them during re-inflation of truck/equipment tires.
All in all, the frame seems light compared to the homemade ones I've seen that were severely dented from mishaps. As you noted the forces can be tremendous. If you take the 295 psi and apply it to the contact area of a split rim (which might be around 100 square inches) you get a reasonably high force!!
RE: How to evaluate the resistance of a wire mesh by calcs ?
As suggested by Ron, is it ok to assume if the tire is inflated at 295 psi and the total contact surface is 100 sq.in you get a force of 29.5 kips, Is it ok to apply this force on the HSS tubing of the cage ?
RE: How to evaluate the resistance of a wire mesh by calcs ?
I have no real feel for the forces....I gave you a guess as to an approach. JS might have a better feel for it.
My experience comes from getting tires repaired, and standing there while they were completed. I've seen a split rim retaining ring pop over the rim. It lifted the cage off the floor. That was on a 22-inch diameter rim on a typical semi-trailer.
RE: How to evaluate the resistance of a wire mesh by calcs ?
You can make some reasonable engineering assumptions and with some experience and judgement start to hone in one the capacity of the cage. You must know all of the details of the cage construction; mechanical properties of the various materials used, the welding details, etc. Then I would start by thinking about and calculating the capacity of a single wire at its yield or ultimate strength and a tolerable deformation; then two or three wires. Then, under the worst conditions how do these wire forces affect the tube structural members and the wire welds to the tube structure. You would like everything (all structural elements) to start to yield, or collapse around the failing tire at about the same time to absorb the max. energy of this dynamic action (problem). And, still the big engineering difficulty is determining these actual dynamic forces and displacements, and setting some limit for an acceptable outcome. I would think it might be reasonable and acceptable to assume that the cage was essentially destroyed after a tire or rim failure, and having saved a life. And, I would expect some pretty big dents and deformations from lesser failures. For a seemingly simple apparatus, this is really quite a complex engineering problem the way you have asked it.
RE: How to evaluate the resistance of a wire mesh by calcs ?
TTFN
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RE: How to evaluate the resistance of a wire mesh by calcs ?
RE: How to evaluate the resistance of a wire mesh by calcs ?
A more rigorous approach would take into account the velocity of the chunk and the dissipation of the pressure wave as it expands.
TTFN
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RE: How to evaluate the resistance of a wire mesh by calcs ?