H-20 loading, also known as HS-20 loading, is the bridge design criteria established by the American Association of State Highway Transportation Officials, states the National Precast Concrete Association Foundation. It specifies truck axle loading of 32,000 pounds or wheel loading of 16,000 pounds.
Although the AASHTO bridge design criteria did not specify loading on construction castings, only one tire can typically be on a casting at a time due to casting size, explains the NPCA foundation. Contractors often ask for a casting to follow the design criteria of 16,000 pounds when asking for H-20 loading.
Following the design criteria ensures that contractors obtain quality construction castings. In 1989, the AASHTO published the AASHTO M306 and revised it in 2005. This specification requires castings to keep a proof load of 40,000 pounds applied on a 9-inch by 9-inch pad in the center of the casting. The 40,000-pound proof load signifies a 2.5 safety factor over the H-20 design load of 16,000 pounds.
Medium duty castings can carry loading ranging from 16,000 to 40,000 pounds, and it can receive traditional loading, according to the NPCA foundation. Traffic-rated castings meet the AASHTO M306 proof load, with a loading criterion of 40,000 to 100,000 pounds. Airport-rated castings accept loading from 200,000 pounds and above.