Evaluation of natural periods and modal damping ratios for seismic design of building structures

A comprehensive technique for identification of modal properties (i.e. natural periods and equivalent modal damping ratios) of building structures is presented. The proposed identification technique employs a combination of multiple system identification methods; it utilizes the benefits and suppresses the shortcomings of each method to provide a succinct set of modal properties for building structures. Using the proposed modal identification technique, modal properties of 80 buildings with a total of 896 distinct seismic event and building direction records were identified. Simplified and practical equations for modal quantities along with the variation of such parameters for different structural system types, building height, and amplitude of excitation are studied and presented. A critical assessment of other similar studies and results are presented.