Blue Book Article 1.03.010
For many years model code provisions for earthquake design have acknowledged three fundamental assumptions: 1. Nonlinear, inelastic behavior is expected, but proposed designs may be analyzed with linear procedures. 2. Cyclic loading is expected, but structures may be designed for monotonic loads. 3. Real deformations will greatly exceed those predicted by linear analysis with reduced forces, but the real values may be approximated as multiples of the linear analysis results. Taken together, these simplifying assumptions have made it possible to understand, predict, and regulate structural response in terms suitable for adoption in building codes. Over time, additional code provisions have developed to account for cases in which one or more of these assumptions does not apply.