Starting Estimates of Seismic Site Coefficients along 2D Semi-Elliptical Shaped Hills

Abstract eng:
In the recent past, there have been numerous cases of recorded motion and observed earthquake damage pointing toward topographic amplification as an important effect. Very high recorded accelerations during earthquakes have been sometimes attributed to topographic effects of hills as one basic type of local surface irregularities. In this paper the results of a comprehensive parametric study for estimating the site coefficients in areas with 2D semi-elliptical shaped hills has been presented. Using adequate number of accelerograms as well as numerically calculated transfer functions of 2D semi-elliptical shaped hills, the extension capability of the Borcherdt’s method to 2D semi-elliptical shaped hills has been investigated. By frequency domain analysis and then inverse Fourier transform, the amplified accelerograms along the hills were obtained. The achieved results accentuated the efficiency of the Borcherdt’s method in 2D microzonation studies. Moreover, it has been shown that the site coefficients vary between 1.0 and 1.7, are comparable to the 1D site coefficients usually suggested by the seismic codes, differ from short to long periods and exceed the maximum value of 1.4 proposed by the AFPS (1990) code for seismic design of structures in topographic areas.

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