Wheel Load Distribution on Road Plate

[MLBajorek]

A collegue of mine asked me about the proper wheel load distribution for H-20 loading on a temporary "road plate" used to cover a trench.

Looking through the AASHTO code, I didn't find anything applicable to spanning with plate steel. Did I miss it somewhere?

Thanks for all of the tips. I read much more than I post...

 

[Umassengr]

Use the simple span distribution of the wheel load if you are concerned with the reactions at each end of the trench , but conservatively in this situation I would assume the load is 1/2 the axle load, say 16 Kips.Road plate is not typically designed. The distribution of the wheel load is more for stringer and girder design. There is a distribution for flat slabs that are loaded perpendicular to traffic, but this is more for concrete slab bridges.

 

[strainman]

There are formulas in AASHTO. One for point loads and one for uniform loads, that will give you the percentage of load that is carried by each direction.

with a: being the short span
b: being the long span

Point load short span is b^3/(a^3+b^3)

Point load long span is a^3/(a^3+b^3)

Some judgement will be required to establish the effective width of plate that carries the wheel. But with the wheel contact area of 20", I would not hesitate to double that width for the effective width of plate.

 

[JStephen]

I would assume that the plate would fail by bending at a line in the middle, and solve for average moment at that line. Treating the wheel load as a point at the center of the plate would be conservative. You could assume pressure approximately equal to tire pressure to spread it out over a larger area (75-100 psi for large trucks).

Is that AASHTO distribution above based on plate supported on two sides or is that for support on four sides?

 

[strainman]

The distribution formulas are for two way action.

 

[JStephen]

Seems like the load carried in the transverse direction would be zero if the the sides of the plate are unsupported. There's no place to carry that load to.

 

[MLBajorek]

Thanks for all of the comments. It's a continuous trench for practical purposes, so the sides are unsupported. I would have thought double the wheel contact area reasonable, but was looking for something to back it up with.