When purchasing a bolted steel tank or a welded steel water storage tank, one of the key criteria determining the design parameters of the tank is the Seismic Use Group (SUG) classification. The term Seismic Use Group is essentially the same as the terms Occupancy Category and Risk Category used by the International Building Code (IBC) and the American Society of Civil Engineers (ASCE). The Seismic Use Group classification is used to determine the magnitude of environmental loading applied to the bolted or welded tank structure. Despite the name, the Seismic Use Group classification is applicable to other environmental loads such as wind, snow, ice, and floods.
The Seismic Use Group along with the seismic accelerations at the site help determine the Seismic Design Category of a structure. Seismic Design Category is a letter rating from A to F with F being the worst case. There are special detailing requirements depending on what Seismic Design Category a structure is in. For example, with steel water storage tanks, the seismic design category impacts how the anchor bolts are designed.