Simplification of Earthquake Accelerograms for Rapid Time History Analysis Based on the Impulsive Load Concept

Abstract eng:
Regarding that the time history analysis, as the most realistic seismic response analysis method, is very time consuming, in this paper a method is proposed for simplification of digitized accelerograms by using the concept of impulsive load. In the proposed method, the accelerogram, which is actually a numerical array with the time step size of 0.02, 0.01 or even 0.005 seconds, and usually contains several thousands of time steps with their corresponding acceleration values, is substituted by a limited number (usually less than just a few hundreds) of discrete values, each one equivalent to the area created by the acceleration curve and the time axis between two of its subsequent zero-crossings. These discrete values, which are obviously positive and negative one after the other, multiplied by the mass of the SDOF system, can be considered as a series of impulsive loads, applied consequently to the system, which is subjected to the base acceleration. Using the simple formula of response to impulsive load, response of the SDOF system to base acceleration can be calculated as the summation of its responses to the series of impulsive loads, created by the described method for any given accelerogram. Several numerical examples are presented in the paper to show the efficiency of the proposed simplification technique. Numerical results show that the amount of error of peak response calculation is usually less than 5% for most of earthquake records, while the required time for response calculations is generally only 10% of that of the conventional time history analysis, or even less than that.

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