Seismic Design of Lightweight Metal Building Systems

As a result of failures uncovered after the Northridge earthquake, the AISC Seismic Provisions for Structural Steel Buildings has become extremely stringent in its design provisions for moment frame structures. Although the changes are justified, they are not necessary for every type of building system. Some structures can be safely designed to resist earthquake forces elastically without concern of structural collapse. Metal buildings are typically lightweight, and small inertia forces from the design earthquake will not usually result in an inelastic response of a system that is properly designed to resist wind forces. In this paper, metal building systems are analyzed using an equivalent lateral force method and a linear time history analysis to show that typical metal building systems will respond elastically to the design earthquake. Specifically, using the International Building Code along with the aforementioned document, it is shown in the following sections that for lightweight metal building structures, adherence to the AISC Seismic Provisions for Structural Steel Buildings is not required in most cases except for locations on the West Coast and a few regions east of the Rocky Mountains. Elastic design methodology is discussed and design recommendations applicable to metal building systems are provided.