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by H. Sedarat,
S. Gupta, and S. Werner
January 1994, 43 pp.
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Abstract
Torsional response characteristics of three regular buildings in San Jose, and one in
Watsonville, California, were studied by analyzing the strong motions recorded in these
buildings during three recent earthquakes: 1989 Loma Prieta, 1986 Mt. Lewis, and 1984
Morgan Hill. The story shear forces, torsional moments and dynamic eccentricities in
these buildings during the three earthquakes were obtained from an analysis of the
recorded motions. The fundamental period of vibrations and damping ratios for these
buildings were also estimated for the three earthquakes by using the Fourier Amplitude
Spectra of the recorded motions. These results were then compared with the provisions
of the 1988 Uniform Building Code. The results of our investigation indicate that the
provisions of the 1988 UBC may sometimes not be adequate to realistically account for
the torsional response of buildings during earthquakes, especially for steel moment
frame buildings. The results of this investigation also indicate that the fundamental
building period obtained using Method A in the 1988 UBC may be longer than the actual
period of the building during earthquakes, especially for stiffer low to medium-rise
buildings. This could result in unconservative estimate of earthquake design forces
when using the static force procedure of the 1988 UBC.
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