Numerical Iteration Scheme to Generate a Response-Spectrum- Compatible Accelerogram

The input motion for seismic analysis of building structures is generally specified in design codes in terms of response spectrum. Therefore, real or simulated time histories for ground motions whose response spectrum matches approximately the design spectrum is desired. Among the various techniques currently available for generating spectrum compatible time histories it is possible to distinguish two groups. One group consists of those methods in which the Fourier spectrum of a trial time history is modified to produce desired modifications in the response spectrum. This group could be referred as frequency domain iteration methods. The second group corresponds to those methods in which the solution proceeds from an initial time history approximation, which is modified in successive steps resulting in uniform convergence to the target spectrum. This second group could be called time domain iteration methods. In this research, iteration in time domain method is used to generate a spectrum compatible time history record. This method has application criteria that must be satisfied, and this fact limits its application in some way. In this research, those difficulties are minimized by a proper implementation of an iteration scheme which ensures stability and convergence of the numerical calculation. The modified time histories closely resemble characteristics and appearance of the corresponding unmodified earthquake time histories and, at the same time, their spectrum closely match the target spectrum. Key-Words: Simulated earthquake record, response spectrum, vibration frequency