Steel Moment Frame for High Seismic Zones

The design and construction of structural systems of a building subjected to seismic activity are strongly affected by its seismic design category (SDC). The seismic design category is determined by three parameters: geographic location, underlying soil stiffness, and building importance or use. Seismic categories range from A (lowest) to F (highest). Seismic design category E corresponds to buildings of occupancy groups or risk categories I, II, and III in areas near major active seismic faults. Seismic design category F corresponds to buildings of occupancy groups or risk category IV in areas near major active seismic faults. Risk category I to III buildings are typical buildings (offices, apartment buildings, etc.), and risk category IV buildings are essential buildings that must be functional after seismic events (Hospitals, fire stations, etc.).

Building with seismic design categories E and F have the most restrictions on the types of structural systems and connection details and require the most care in design and construction. Unlike structures in low seismic zones, structures in high seismic zones must be designed for ductile behavior to anticipate inelastic straining. Therefore, steel ordinary moment frames are not allowed in high seismic zones. Steel special moment frames should be used instead. One way to account for ductile behavior in special moment frames is to provide a protected zone from the connection location to a certain distance where welded shear studs and decking attachment are prohibited. Attachments for perimeter edge angles, exterior facades, partitions, duct work, and other construction should not be placed within the protected zone. However, decking arc spot welds to secure decking are permitted within a protected zone.