Design of buildings for lateral forces requires a greater understanding of the load mechanism than many other aspects of structural design. To fulfill this need, this section provides a basic overview of current practice in seismic and wind design. It also discusses recent changes in design provisions and recent developments that will have an impact on future design.
There are fundamental differences between design methods for wind and earth-quake loading. Wind-loading design is concerned with safety, but occupant comfort and serviceability is a dominant concern. Wind loading does not require any greater understanding of structural behavior beyond that required for gravity and other loading. As a result, the primary emphasis of the treatment of wind loading in this section is on the loading and the distribution of loading. Design for seismic loading is primarily concerned with structural safety during major earthquakes, but serviceability and the potential for economic loss are also of concern. Earthquake loading requires an understanding of the behavior of structural systems under large, inelastic, cyclic deformations. Much more detailed analysis of structural behavior is needed for application of earthquake design provisions, because structural behavior is fundamentally different for seismic loading, and there are a number of detailed requirements and provisions needed to assure acceptable seismic performance. Because of these different concerns, the two types of loading are discussed separately in the following.
—–9.1. Description of Wind Forces
—–9.2. Determination of Wind Loads
—–9.3. Seismic Loads in Model Codes
—–9.4. Equivalent Static Forces for Seismic Design
—–9.5. Dynamic Method of Seismic Load Distribution
—–9.6. Structural Steel Systems for Seismic Design
—–9.7. Seismic-Design Limitations on Steel Frames
—–9.8. Forces in Frames Subjected to Lateral Loads
—–9.9. Member and Connection Design for Lateral Loads