MODAL-ANALYSIS OF LINEAR DYNAMIC-SYSTEMS - PHYSICAL INTERPRETATION

The modal analysis procedure for calculating the dynamic response of c lassically damped linear structural systems is reformulated with the o bjective of developing the physical significance of the elements of th e solution and defining modal contribution factors. The resulting conc epts are used to develop an-approach for predicting how the relative c ontributions of various modes to the response and the number of modes that should be included in the solution depend on the vibration proper ties of the system, on the response quantity of interest, and on (1) t he spatial distribution and time variation of applied dynamic forces i n the case of force-excited systems, or (2) the response (or design) s pectrum for an earthquake excitation. To illustrate this approach, num erical results are presented for a five-story frame for a wide range o f parameters and a base-isolated building.