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by W. Silva and G. Toro
Silva, W., and G. Toro (1996). Verification of Response Spectral Shapes and Anchor Points for Different Site Categories for Building Design Codes. SMIP96
Seminar on Seismological and Engineering Implications of Recent Strong-Motion Data, p. 37 - 52.
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Abstract
The dramatic increase in strong ground motion recordings over the last several years has provided both the impetus and
opportunity to empirically examine the seismic design criteria in both the UBC and NEHRP code provisions. In this
project both spectral design shapes and the usefulness of two spectral anchors are investigated using a comprehensive
strong motion database and updated empirical attenuation relations. For the shapes, the results suggest that both the
UBC and NERHRP design spectra provide enveloping criteria (except for site D at short periods) including cases for sites
within 10 km of the fault rupture surface. For the NEHRP design spectra, comparison of the Fa and Fv factors to those
implied by a recently developed empirical attenuation relation suggest that the NEHRP Fa factors may reflect too little
nonlinearity while the Fv factors may show too much nonlinearity. Comparisons of the code shapes to the results from
probabilistic seismic hazard analyses indicate that the fixed UBC shape has a moderate tendency to under-predict
amplitudes for T > 1 sec in places like San Francisco and Sacramento where large (M > 7) earthquakes dominate the
hazard at these periods. The more flexible NEHRP shape avoids this problem, but requires the specification of two
anchoring points.
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