The Earthquake Engineering Online Archive

Vibration properties of buildings determined from recorded earthquake motions

Goel, Rakesh K.; Chopra, Anil K.

UCB/EERC-97/14, Earthquake Engineering Research Center, University of California, Berkeley, 1997-12, 271 pages (575/G63/1997)

Most seismic codes specify empirical formulas to estimate the fundamental vibration period of buildings. Developed first in this investigation is a database on vibration properties -- period and damping ratios of the first two longitudinal, transverse, and torsional vibration modes -- of buildings "measured" from their motions recorded during eight California earthquakes, starting from the 1971 San Fernando earthquake and ending with the 1994 Northridge earthquake. To this end, the natural vibration periods of 21 buildings have been measured by system identification methods applied to the motions of buildings recorded during the 1994 Northridge earthquake. These data have been combined with similar data from the motions of buildings recorded during the 1971 San Fernando, 1984 Morgan Hill, 1986 Mt. Lewis and Palm Springs, 1987 Whittier, 1989 Loma Prieta, 1990 Upland, and 1991 Sierra Madre earthquakes reported by several investigators. The "measured" fundamental periods of moment-resisting frame and shear wall buildings, extracted from the database, are then used to evaluate the empirical formulas specified in present U.S. building codes. It is shown that although current code formulas provide periods of moment-resisting frame buildings that are generally shorter than measured periods, these formulas can be improved to provide better correlation with the measured period data. The code formulas for concrete shear wall buildings are, however, inadequate. Subsequently, improved formulas are developed by calibrating the theoretical formulas against the measured period data through regression analysis. Factors to limit the period calculated by a "rational" analysis, such as Rayleigh's method or computer-based eigen-analysis, of both types of buildings are recommended for code applications.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-97-14.pdf (18 MB)