Empirically Derived Design Spectra
Basic Concepts

The complexity of the previous methods, and the limited number of records available two decades ago, led many investigators to develop empirical methods for developing design spectrum from estimates of peak or effective ground motion parameters. These relationships are based on the concept that all spectra have a characteristic shape, which is shown below.

From observation of the above spectra, it can be seen that the maximum acceleration, velocity, and displacement occur in different period ranges. In addition, the maximum value is usually contained in a region where the spectral values are nearly constant. The spectrum can then be roughly divided into three regions: a region where acceleration is nearly constant, one where velocity is nearly constant, and one where displacement is nearly constant.

N. M. Newmark and W. J. Hall developed a particularly simple and useful procedure for applying these basic principles to the development of elastic design spectra, which is explained in detail in the next page.