Appendix—Historical Development of Building Code Seismic Provisions

Abstract

Buildings that experience earthquake ground motion at the base will move with the ground and vibrate. To be successful, the design criteria and the resulting design must be able to produce a structure that will adequately resist any earthquakes that will affect the building during its intended useful life, including, in some cases, multiple earthquakes. The building code specifies the minimum amount of strength that will be required to satisfy specific risk criteria. Traditionally, most building codes have required that structures be designed to resist static lateral forces, which are a percentage of the vertical self-weight of the building. Vertical seismic forces are generally not included because it is generally thought that static gravity loads plus normal factors of safety should be adequate to resist the vertical effects of the earthquake motion. However, details must be carefully designed to provide for stress reversals and inelastic deformations (ductility). In addition, connections must be able to provide the necessary overstrength. If the previous conditions are satisfied, the structure should be able to withstand minor earthquakes with limited nonstructural damage and without structural damage, moderate earthquakes without extensive struc- tural damage, and major earthquakes without collapse. A well-designed structure should also minimize economic loss in the event of a moderate or strong earthquake. This requires careful attention to such things as material properties, connection details, and workmanship, which cannot be explicitly required in the code. The following brief history of building codes provides background for the development of these codes as well as the building code requirements for older buildings that may still be in use and in need of strengthening.