UNCOUPLED FREQUENCY RATIO IN ASYMMETRIC BUILDINGS

Structural eccentricity and Uncoupled Frequency Ratio (UFR) are two sy stem parameters that strongly influence the elastic response of eccent ric structures. The opinions differ regarding their influence on the i nelastic response. Different investigators arrived at contradictory co nclusions on the influence of uncoupled frequency ratio. The reasons f or these contradictions are the use of different definitions and diffe rent models in the inelastic studies. In this paper, three possible de finitions of the uncoupled frequency ratio are identified, and their i nfluence is studied on the inelastic response. An ensemble of 10 real earthquakes of 20 s duration is used. The response is measured in term s of the mean plus one standard deviation of the ductility ratio. The value of the UFR obtained by each of the three possible definitions is not always admissible, It is concluded that the inelastic response de pends upon the eccentric system, definition employed for the UFR, time period of the eccentric systems and the basis of strength distributio n among the various lateral elements.