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|Title:||Corps of Engineers Strong-motion Instrumentation Program. Report 1, Earthquake response spectral analysis of Arkabutla Dam, Mississippi|
|Authors:||United States. Army. Corps of Engineers. Lower Mississippi Valley Division.|
Chang, Frank K.
New Madrid earthquakes
|Publisher:||Geotechnical Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; GL-90-10 rept.1.|
Abstract: This report provides a permanent documentation for and presents an analysis of the accelerograms for the main shock and aftershock of the New Madrid earthquakes of 25 March 1976 obtained at the Arkabutla Dam, Mississippi. Both epicenters occurred in Arkansas at latitude 35.6°N, longitude 90.5°W. The preliminary results of t he integration of 12 accelerograms recorded at the Arkabutla Dam were published by Herrmann (1977). The main purposes of this study are to analyze the response spectra of acceleration, velocity, and displacement, the amplification factors, and the natural periods of foundation, dam, and abutment. All response spectra of longitudinal (L), vertical (Z), and transverse (T) components for the downstream (toe), crest, and abutment of Arkabutla Dam were presented individually. Five percent damped spectral amplitude-ratios of the L-component at the toe to those at the abutment and the similar crest to the abutment rates were 4.2 and 2.2, respectively, at the period of 0.35 sec or 2.9 Hz. Therefore, 0.35 sec is the natural period for both foundation and dam. Evidently, the spectral amplitude of the L-component at 0.35 sec on the crest of the dam was deamplified or reduced directly due to the dissipation (attenuation) of wave energy in the dam. Also, the acoustic impedance of the foundation and the acoustic impedance of the dam were approximately the same. The average amplification factor of the vertical component for the toe relative to the abutment is 3.22 for the period of 0.25 sec or 4Hz; for the T-component it is 1.06 and 0.93 for 0.35 sec (2.9 Hz) and 0.40 sec (2.5 Hz), respectively. The natural periods or natural frequencies determined from the observed response spectra of the foundation are 0.35 sec (2.9 Hz), 0.25 sec (4.0 Hz), and 0.38 sec (2.6 Hz) for L-, Z-, and T-components. For the dam, the natural periods are 0.35 sec (2.9 Hz), 0.33 sec (3.0 Hz), and 0.38 sec (2.6 Hz) for L-, Z-, and T-components, and for the right abutment the natural periods are 0.35, 0.35, and 0.38 sec for L-, Z-, and T-components.
|Rights:||Approved for public release; distribution is unlimited.|
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