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H-20 Plate Design

H-20 Plate Design

H-20 Plate Design

(OP)
I need to design a plate inside a private business that is to go above a drainage pit. The plate is required to be designed for H-20 loading. I have an old formula in my notes that is as follows Moment = 0.5(S+2). This formula will give the required moment strength of the plate in ft-kips/ft and I believe is came from an old AASHTO code. Is this the correct formula to be using? FYI, my pit width is 4'-0"

RE: H-20 Plate Design

I think that formula is for a simply supported slab......not one supported on 4 sides. For that condition, AASHTO has a formula to distribute the moments. You could just do it by hand by putting a 16 kip load (with impact factors) at the center of the plate. (Assuming the loading you are referring to is HS20-44 [Standard Truck].) A lot of times deflection [L/800] winds up controlling anyway. Usually for a pit cover, you come out with 3/4" Plate.

RE: H-20 Plate Design

SteelPE - If you find the reference for that formula I'd be interested in knowing where it came from. I couldn't find it in any of the AASHTO/AASHO Standard Specs, going back to 1953. There wasn't anything in an AISC publication from 1938 on battledeck floors (the forerunner of orthotropic decks).

I agree with WARose; 3/4" should be fine for strength. IN NYC, contractors typically use 1" or more for plating because the City has a 3/4" deflection limit.

RE: H-20 Plate Design

(OP)
bridgebuster.,

It is a formula for concrete slabs that can be found in ASSHTO but I don't see how it wouldn't apply here. I ended up finding the formula in AASHTO (17th edition equation 3-15). The equation was reduced from what is given in AASHTO.

Using this formula I calculated a required thickness of .78 inches. I was going to round it up to 1-1/4" but decided to go with 1" thick. It's good to hear that I am at least in the ballpark and slightly heavy for strength.

One issue I have is that the pit cover is made up of two 6' long plates and a 4' section of grating. So I have a free edge on the plate. I didn't like that so I put a 6x4 tube on the free end to support the load as it transfers from the grating to the plate

RE: H-20 Plate Design

SteelPE - Boy, am I a dopehairpull3 P/32 = 0.5

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