What is H-20/HS-20 Loading?
AASHTO's H-20 and HS-20 are live load ratings applied to the design of bridges or other suspended items (e.g. lids for concrete vaults). Designers use H-20 or HS-20 from AASHTO, or specific axle configurations, to express the extreme load effect created by heavy vehicles such as transports, buses and fire trucks. These in turn are used to calculate the moment (bending) and shear acting on a bridge or other suspended segment as the vehicle passes over it. For example, the lid of a concrete vault would need to be able to support the specified loading to make sure a heavy vehicle will not collapse the lid and fall into the vault itself.