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Steel Plate Check

Steel Plate Check

Steel Plate Check

(OP)
I have a trench that spans 7 ft. and a steel plate is needed for a load of 16 kips plus impact. I need to check if a 1.5 thick plate works. Also how to get the stresses? Any suggestion? The plate is free at two ends and simply supported at the other two. fy = 36 ksi.

Thank you

RE: Steel Plate Check

Yield line analysis probably

RE: Steel Plate Check

16 kips plus impact -- sounds like we're talking about public traffic loading, correct?

I've yet to find a good reference for yield line analysis, so maybe that helps you out enough to make it work. Do you know of one CanWest?

But my gut feel (without yield line) is that 7' is too long a span for 1-1/2" A36.

RE: Steel Plate Check

Analytically you can use yield line, or ready tables. There are suitable tables of pre-solved moments in the Structural Engineering Formulas by Ilya Mikhelson.

RE: Steel Plate Check

I ran it myself on STAAD (i.e. a 7'x14'x1.5" A36 steel plate; simply supported on the long sides, free on the short sides). I spread it (i.e. a single 32 kip load, I used a factor of 2 for impact) over 144 in^2 at mid-span/center of the plate. This assumes we are talking about a tire here. Results: Max. Deflection= 0.423". Max shear stress= 289 psi. Max. Principal stress= 19.9 ksi.

Back checking the stress with a simple-span model, it's about what I would expect to get if about 7' of the plate was engaged to resist the (developed) moment.

A critical condition occurs when the plate is loaded near a free edge (@ mid-span). In that case, you have stresses more than twice what I quoted. Not sure if that can happen in your case.....but wanted to advise.

RE: Steel Plate Check

Quote (WARose)

I ran it myself on STAAD (i.e. a 7'x14'x1.5" A36 steel plate; simply supported on the short ends, free on the long sides). I spread it (i.e. a single 32 kip load, I used a factor of 2 for impact) over 144 in^2 at mid-span/center of the plate.

Did you mean to say simply supported on the long sides, free on the short ends?

BA

RE: Steel Plate Check

Correct BA.....good catch. I altered my post to fix that (and add some more info).

RE: Steel Plate Check

Can you use Z=b*d^2/4 for the plastic section? Advantage with plastic design as well as strength is isotropic, ie. moment resistance same about any axis.

Dik

RE: Steel Plate Check

daranguiz beat me to it. That publication is for concrete but the same principles apply for steel. For this plate, consider a yield line parallel to the supports at the location of the load (failure as if it were a 1D beam), diagonal yield lines from the point load to the corners, then diagonal yield lines going from the location of the load to any point along the unsupported edge. I do this in Mathcad and vary the dimensions until I find something critical.

RE: Steel Plate Check

The dimension of the plate parallel to the trench has not been given. The answer to the problem will be much different for a square plate (7' x 7') than it is for a very long plate.

The nature of the impact has not been given; the impact factor cannot be determined with precision.



BA

RE: Steel Plate Check

(OP)
Thanks for all the help. The plate is 15x8. 15ft spans the 7 ft trench while 8ft is parallel to the trench.

Yes public traffic loading.

IM = 1.3

RE: Steel Plate Check

Quote (RG4)

The plate is free at two ends and simply supported at the other two.

Quote (RG4)

The plate is 15x8. 15ft spans the 7 ft trench while 8ft is parallel to the trench.

How can this be? If true, the span of the plate is 15'-0" which does not make sense.

Are there additional supports at each edge of the trench? In that case, the plate is not a simple span.

Perhaps a sketch showing the 15x8 plate and the location of the supports would be helpful.

BA

RE: Steel Plate Check

BA, If I'm envisioning this correctly, He's covering an approximate 7' wide trench opening with a giant piece of steel plate that overhangs the trench 4' on each side. Which seems unrealistic. It would weigh over 6000lbs. Seems kind of unlikely that is manageable to move around.

RE: Steel Plate Check

It doesn't make sense to me either, jayrod. I think we need more information from RG4.

BA

RE: Steel Plate Check

Often in these large span grate situtations you have small columns that reduce the spans down but dont affect the flow to much.

http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

RE: Steel Plate Check

(OP)
BA, If I'm envisioning this correctly, He's covering an approximate 7' wide trench opening with a giant piece of steel plate that overhangs the trench 4' on each side. Which seems unrealistic. It would weigh over 6000lbs. Seems kind of unlikely that is manageable to move around.

You're correct jayrod. The trench is 7ft by 18ft and the trench plate is being placed in a way that 15ft spans over the trench so 4 feet is pass the trench on each side. Couple plates are needed to cover the trench. Hope that helps.

RE: Steel Plate Check

Ok but why a 15 ft long piece of plate. The 4 ft overlap seems wasteful

RE: Steel Plate Check

Road plate often is kept in a contractor's yard -- and with the right equipment isn't too bad to move around, even if oversized. Not worth the trouble to cut -- especially since it'll be picked back up and re-used in a few months.

RG4 -- since the plate overhangs each end, it's worth talking about what is at the edge of the trench. Is this an excavation across a flexible pavement (asphalt) or soil that might lead to an effective span longer than 7'? Or is there concrete or a braced element that will keep the point of support rigid at the edge of the trench?

RE: Steel Plate Check

(OP)
You're 100 % correct Lomarandil.

the Excavation is on dirt and is only 6 ft wide but since it is on dirt you are right the span is longer which is why im saying the trench is 7ft but rather the span is 7 ft.

Would yield line be best to use?

RE: Steel Plate Check

Hard to say what the span is; certainly more than 6', quite possibly more than 7', depending on the type and stability of the soil each side of the trench.

The most critical condition occurs when the load is applied at or near the edge of a plate. A "couple" of plates will not cover the trench in the orientation described above. Three plates would be required to cover a 6'x18' trench. It may be a good idea to place one plate centrally on the trench and allow the other two to overlap 2' on each side, leaving a 4' gap in the middle. This would ensure that neighboring plates share the load while mutually covering a 20' length of trench.

Yield line theory is likely best for determining the capacity of the plates.

BA

RE: Steel Plate Check

(OP)
That's a good idea BA. Cant I just treat it as a simply supported beam with a concentrated load in the middle? But what would be the effective width to calculate the section modulus? Any suggestions?

Thank you everyone for their help.

RG4

RE: Steel Plate Check

Yes, a beam with concentrated load at midspan. I would consider the span to be about 9'-0" or 10'-0", recognizing that the bearing surface may not be perfectly flat and that some spalling could occur at the edge of the trench. On that basis, I would consider the effective width of plate to be 8'-0". With yield line theory, you do not need section modulus. You need plastic modulus bt2/4 with b = 96" and t = 1.5".

If you are interested in service stresses or deflections, you might want to use a somewhat smaller effective width, depending on where the load is located relative to the middle of the plate, perhaps about 6'-0" would be about right for worst case positioning.

BA

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