I am trying to design a box culvert cover to be traffic rated and heelproof. For the heelproof, I have found that a gap of 1/4" or less will meet the local standards. The "traffic rated" part has me concerned. I have looked at many manufacturers of grating and all will supply me a grate that is H-20 rated. When I ask (out of my own curiosity) what the actual loading is for H-20 in psi or load over area, they all say that it is based on a 32k axle. This does not tell me what the actual loading is. Is there a call out for the loading of one tire? What is the size of that tire in contact with the grate? I have searched the internet and have found nothing stating the tire size and tire load.
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AASHTO H-20, HS-20. . . 1
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AASHTO Loading of either H-20 or HS-20 is based on an axle load of 32 kips. This load is divided into two tires; that is a load at each end of the axle. The tire area contact is defined in AASHTO 3.30 Tire Contact Area
The tire contact area for HS 20-44 shall be assumed as a rectangle with a length in the direction of traffic of 10 inches, and a width of tire of 20 inches.
Therefore, the pressure would appear to be equal to 16 kips / (10" x 20") = 80 psi or 11.5 ksf. In case you need to know, these two tires on the axle are spaced six feet apart (center-to-center) transverse to the direction of traffic and the successive axles of an HS truck are 14 feet apart along the direction of traffic.
Good Luck.
The tire contact area for HS 20-44 shall be assumed as a rectangle with a length in the direction of traffic of 10 inches, and a width of tire of 20 inches.
Therefore, the pressure would appear to be equal to 16 kips / (10" x 20") = 80 psi or 11.5 ksf. In case you need to know, these two tires on the axle are spaced six feet apart (center-to-center) transverse to the direction of traffic and the successive axles of an HS truck are 14 feet apart along the direction of traffic.
Good Luck.
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bridgebuster
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If it's a true culvert (span < 20') the impact would be 30%.
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The span is 12'.
The reason for this is that I am very suspicious of the supplier. The design calls for 2-16"wide x60long" grated areas (1 in each lane) to drain directly through the top of the culvert to the waterway below. The supplier showed me a sample grate that was only 3/4" thick and said that it was rated for traffic loads.
I want to know what parameters that I can use to test these grates so that I know I am not putting grates in traffic lanes that will fail. The final dimensions of the grates are 16" wide x 20" long. They are resting on a frame that is poured into the culvert top.
The reason for this is that I am very suspicious of the supplier. The design calls for 2-16"wide x60long" grated areas (1 in each lane) to drain directly through the top of the culvert to the waterway below. The supplier showed me a sample grate that was only 3/4" thick and said that it was rated for traffic loads.
I want to know what parameters that I can use to test these grates so that I know I am not putting grates in traffic lanes that will fail. The final dimensions of the grates are 16" wide x 20" long. They are resting on a frame that is poured into the culvert top.
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