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CPENG78 (Civil/Environmental) (OP)
4 Jan 10 18:42
This may be a shot in the dark but here it goes. I have an existing 4 ft x 8 ft x 12 ft deep existing concrete vault (appears poured in place). At the top of the vault there is a steel frame supporting 4 ft long I-Beams (about 6" deep) at 13" on center. These beams support 4 solid plates (grates) serving as the cover to this vault. The plates are flushed with existing ground and are to be flushed with the proposed pavement for a new parking lot been proposed.

The proposed parking lot will have approximately 75 spaces and expected low traffic volume (don't know exaclty how many trips are generated by the faclity but for the moment is expected to be low). The existing vault will lie directly on one of the parking lot's travel lanes.

Now the contractor is been asked to replace the frame and grate for one that is traffic rated. However is there a way to show that something existing would be H-20 traffic rated? There are no logos or part numbers that appear on the existing frame and grate system.

Your thoughts/suggestions would be appreciated. Thanks.
cntw1953 (Civil/Environmental)
4 Jan 10 19:14
If there is car to pass, get traffic rated grating, which is readily available from most bar grate manufacturers. Why worry/mess around the old grate? You can do a cal yourself, or by someone else to figure out the ball-part strength though.
bimr (Civil/Environmental)
5 Jan 10 1:43
The H-20 Traffic Rating design must be analyzed and certified by a licensed professional structural engineer. Key to successful implementation of the H-20 design is incorporation of a rebar framework that is carefully assembled and consistently placed in the tank walls.

Without knowing the details of how the concrete was constructed, it would be difficult to have an engineer certify the design.

It would probably be easier to replace than have it certified.
CPENG78 (Civil/Environmental) (OP)
5 Jan 10 12:32
Thanks for the quick responses.

In doing some research I did notice some manufacturers to show that their products (lids, grates, etc) are H-20 rated and then they say for "...ocassional traffic impact...". Is there a limit to how much traffic is allowed on an H-20 rated product? Is there a higher rating than H-20?  
Helpful Member!  bridgebuster (Civil)
5 Jan 10 13:10
I haven't seen any grating with a rating higher than 16K (H-20 or HS-20 wheel load).

My work is primarily in NYC; we use HS-25 for bridge design but the sewer department accepts 16K gratings.

In your case, it doesn't seem that it would take very long to analyze a 6" beam.  
Helpful Member!  JedClampett (Structural)
5 Jan 10 16:10
The manufacturers that say their covers are good for occasional H-20 loading mean they're not for street use.  Repeated wheel loadings will warp the cover.  I think that H-20 is still the maximum load that is designed for. You can get grating that is H-20 rated from Grating Pacific (  Note that grating that spans 4'-0" is 4 inches deep and weighs almost 30 psf.  Another way to go is to use a cast iron grating or cover manufactured by Neenah Foundry.
cntw1953 (Civil/Environmental)
5 Jan 10 19:56
Keep looking. We recently replaced a bridge with grate as deck (rated H-20), the bars are in some form, and is about 5" deep. I may have some document in the office, If I do, I will post it. Otherwise, it wouldn't hurt to give the manufacturer a call to clear their's intent on such vague language. Although Ralph has explained well, but what is the definition of "occasion"? 10 passes a day, or 100...?
cntw1953 (Civil/Environmental)
5 Jan 10 21:51
Two sample results from web search.
The first (link) is a design criteria for heavy duty bar grate from Ohio Gratings, Inc.
The second (PDF) is a standard detail sheet from the State of New York, DOT.

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