The predominant period and corresponding equivalent viscous damping ratio, also known in various loading codes as effective period and effective damping coefficient, are two important parameters employed in the seismic design of base-isolated and conventional building structures. Accurate determination of these two parameters can reduce the uncertainty in the computation of lateral displacement demands and interstory drifts for a given seismic design spectrum. This paper estimates these two parameters from data sets recorded from a full-scale five-story reinforced concrete building subjected to seismic base excitations of various intensities in base-isolated and fixed-base configurations on the outdoor shake table at the University of California, San Diego. The scope of this paper includes all test motions in which the yielding of the reinforcement has not occurred and the response can still be considered ‘elastic’. The data sets are used with three system identification methods to determine the predominant period of response for each of the test configurations. One of the methods also determines the equivalent viscous damping ratio corresponding to the predominant period. It was found that the predominant period of the fixed-base building lengthened from 0.52 to 1.30 s. This corresponded to a significant reduction in effective system stiffness to about 16% of the original stiffness. The paper then establishes a correlation between predominant period and peak ground velocity. Finally, the predominant periods and equivalent viscous damping ratios recommended by the ASCE 7-10 loading standard are compared with those determined from the test building.
Bibliographical noteFunding Information:
The BNCS project was a collaboration between four academic institutions (University of California, San Diego, San Diego State University, Howard University, and Worcester Polytechnic Institute) and was funded by NSF-NEESR program, grant number CMMI-0936505, the National Science Foundation, the Englekirk Advisory Board, the Charles Pankow Foundation, and the California Seismic Safety Commission, over 40 industry partners and two oversight committees. A listing of project participants may be found on the project website: http://bncs.ucsd.edu/index.html. The accelerometer/GPS Kalman filter analysis was performed by Jessie Saunders and funded by NASA grant NNX14AT33G. Opinions and findings expressed in this paper are those of the authors and do not necessarily reflect the views of the funding agencies.
Copyright © 2017 John Wiley & Sons, Ltd.
- base isolation
- effective system stiffness
- equivalent viscous damping ratio
- predominant period
- shake table testing