Digital filters for earthquake site studies
Carleton, Hendrik D.
Technical reportAbstract: The objective of this study was to develop a computerized technique for processing strong-motion accelerograms from earthquakes in order that earthquake vulnerability for existing structures can be more fully investigated through the use of simplified base excitations. Through filter theory, the Wiener normal equations were used to reduce accelerogram pairs to basic time histories called operators. This approach isolates the differences contained within accelerogram pairs from project sites at which the data were obtained. The operators are used with mathematical shocks (such as half-sine pulses) as inputs to produce simplified responses. Variations in the simplified responses are obtained by changing the durations of the half-sine or other hypothetical wave form inputs and using the same operator for each variation. Each family of responses is then studied to determine its sensitivity to these changes. As an example of this theory, data from an earthquake of magnitude 4.4.were used to construct operators that related free-field motions to those on the main and auxiliary dams at the Isabella Reservoir near Bakersfield, California. Half-sine inputs of 0.1-g peak amplitude and 0.1- to 0.6-sec durations were used to study the sensitivity of the dam responses. The auxiliary dam had a maximum sensitivity to cross-dam excitation when the input duration was 0.4 sec. For this input duration, the response peak acceleration was 2.4 times as great as the input peak acceleration. The main dam showed maximum sensitivity to cross-dam excitation when the input duration was 0.3 sec; however, in this case the response peak acceleration was only 1.3 times as great as the input peak acceleration. Based on the results of this study, it is concluded that use of this technique should enable structural engineers to assess earthquake vulnerability for existing structures more fully, and that this in turn could lead to improvements in future designs.
Weapons Effects Laboratory (U.S.)Engineer Research and Development Center (U.S.)
Accelerograms; Computer applications; Digital filters; Earthquakes; Ground motion; Isabella Dam
Technical report (U.S. Army Engineer Waterways Experiment Station) ; N-75-3.
Approved for public release; distribution is unlimited.