What is load rating, and what is the meaning of H-20? Load rating measures how much weight a manhole cover can handle. Where did this name come from?
Different countries and companies follow different standards when it comes to load ratings. The American Association of State Highway and Traffic Officials(AASHTO) sets the standards for specifications, test protocols, and guidelines in the United States. These guidelines are used in highway design and construction across the nation, which includes load rating regulations. The first meeting of the AASHTO was during World War I, which established AASHTO to address state-level highway needs and priorities. The second meeting focused on the need for federal aid to help improve state roads.
These annual meetings throughout history have helped develop the nation’s transportation network; now, the standard people try to follow in the United States. AASHTO’s published bridge criteria is known as H-20. H-20 Loading consists of truck axle loading of 32,000 LBS or a single point wheel load of 16,000 LBS.
AASHTO’s load rating designations are based on bridges and roadways. Most manhole covers can only hold one wheel at a time, whereas bridges and roads fit entire axles or vehicles. Therefore, the AASHTO load rating may not technically apply. However, engineers may still incorporate the H-20 standard into their specifications.
What is the difference between H-20 and HS-20? In reality, there is no difference between the two when it comes to manhole covers. Since manhole covers can only fit one tire at a time, the full capacity of the load is divided between the number of tires on each axle or vehicle. In the image below, 32,000 LBS per axle, split between two or more tires, equals a single-point wheel load of 16,000 LBS or less.
AASHTO M306 is the newest specification of bridge criteria. It was created in 1989 and completely revised in 2005. AASHTO M306 maintains a proof load of 40,000 LBS applied by a 9-inch by 9-inch pad in the center of the manhole cover. A 40,000 LBS proof load represents a 2.5 safety factor over the H-20 design.
AASHTO defines additional load ratings such as H-25 or HS20-44. To find out more information, reach out to us today.
See our Load Rating blog to find out what product and load ratings are available at ManholeCoversDirect.com.
