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Open Access Publications from the University of California

Estimation of Natural Periods and Damping Ratios for Buildings

  • Author(s): Harris, Angie
  • Advisor(s): Zareian, Farzin
  • et al.
Abstract

This study is aimed at assessing modal parameters (e.g. natural periods and damping ratios) of existing buildings throughout California using system identification techniques. The data accumulated is then analyzed to provide generalized relationships between these modal parameters and building characteristics. The main focus has been on engineering applications, and addressing questions by the engineering community about building modal properties and how they are used to proportion structural components and seismic loss assessment.

The first part of this thesis discusses the estimated modal parameters for ten lateral force resisting systems. Correlations between the natural periods and damping are determined with respect to building heights and dominant building response characteristics. Comparisons are made between the data collected in this study and regressions for these parameters that have been provided by previous studies. There is an agreement in the natural periods estimated through system identification and periods estimated through current code formulas. Likewise, damping values determined in this study remain within the range of current codes values.

The second part of this thesis discusses the application of system identification to the accurate estimation of loss. This portion of the study explores the comparison of natural periods provided through conventional analysis and that estimated through system identification for three lateral force resisting systems. The ratios derived from these comparisons result in the establishment of adjustment factors for natural periods. These adjustment factors are then applied to determine discrepancies in estimated lateral drift, and ultimately loss estimation.

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