Steel Plate Check

[RG4]

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

 

[Lomarandil]

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?

 

[RG4]

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?

 

[BAretired]

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

 

[RG4]

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

 

[BAretired]

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