Simplification of earthquake accelerograms for quick nonlinear time history analyses by using modified Inverse Fourier Transform

Abstract

In seismic design and evaluation of irregular buildings most codes recommend nonlinear time history analysis (NLTHA), which is very time-consuming, mainly since the time step size of the digitized accelerograms is usually very small. Therefore, if the NLTHA analysis can be performed by large time steps without losing much precision, it can be very helpful. This paper introduces a method for simplification of accelerograms based on the modification of their Fourier analyses. In the proposed method the Fourier Spectrum of the accelerogram is calculated first, and then, by using a computer program, developed by the authors, the corresponding Inverse Fourier Transform is calculated using a relatively large time step, depending on the structure's periods, which is usually 5 to 10 times of the original accelerogram's time step) to create the simplified accelerogram. Obviously, time history analysis by using this simplified accelerogram is much less time-consuming. Numerical results show that the maximum response values obtained by using the simplified accelerograms have only 5 to 10 percent error, depending on the type of the structure and the features of the used records.

A Simple Approach Towards Further Accuracy in Structural Dynamic Analysis

“…Two formulations are proposed for the replacement; see [8,51,52], from which, in view of the convergence based nature of the discussion presented in this paper, the first [8,51] is already implemented in the analyses of the proposed approach in the second example studied in the previous section.…”