A NOVEL STOCHASTIC METHODOLOGY FOR THE GENERATION OF ARTIFICIAL SEISMIC ACCELEROGRAMS

ORAL presentation is preferred A NOVEL STOCHASTIC METHODOLOGY FOR THE GENERATION OF ARTIFICIAL SEISMIC ACCELEROGRAMS H. Yanni1, M. Fragiadakis1, and I. P. Mitseas1,2 1 School of Civil Engineering, National Technical University of Athens, Greece 2 School of Civil Engineering, University of Leeds, United Kingdom heragian@mail.ntua.gr; mfrag@mail.ntua.gr; Imitseas@mail.ntua.gr Keywords: artificial accelerograms, non-stationary stochastic processes, spectrum compatible, dispersion, ground motion model Abstract. Dynamic structural analysis requires the use of suites of accelerograms that represent the input ground motion. Hazard consistency may be achieved by matching these records either to a design spectrum or to a ground motion model (GMM). The latter approach is more accurate and provides additional detailed hazard information for the site of interest. Besides, the accelerograms adopted for the seismic simulations can be either recorded, or artificially generated. In this setting, seismic codes (e.g. Eurocode 8) recommend the use of artificial accelerograms; however, they do not propose any specific method allowing engineers to resort in a number of pertinent models proposed in the relevant literature. The herein study proposes a novel methodology for the stochastic generation of fully non-stationary artificial accelerograms that are compatible with a target spectral mean and a target variability. Due to the random nature of seismic actions, artificial ground motion time histories can be represented as stochastic processes using spectral representation techniques [1]. Existing spectrum-based models [2,3] are extended in order to introduce controlled variability which is consistent with the seismic hazard defined by a GMM. Therefore, given the seismic scenario (Mw, R) and the soil conditions, the target spectral mean and variability for each period is obtained from the GMM. Based on those data, multiple target response spectra are generated from a random vector that follows the normal distribution. Artificial accelerograms whose response spectra individually match the produced spectra are subsequently generated. The basis for generating spectrum-compatible accelerograms relies on the relationship between the values of the power spectral density (PSD) function of the ground motion and the response spectral values for a given damping ratio [4,5]. Corrective iterations in the frequency domain are performed in order to achieve enhanced matching and to improve the control of variability. Lastly, the proposed methodology provides with suites of fully nonstationary artificial ground motion time histories whose response spectral mean and variability match those of the assigned GMM. [1] M. Shinozuka, G. Deodatis, Simulation of Stochastic Processes by Spectral Representation, Applied Mechanics Reviews 44(4):191-204, 1994. [2] A. Preumont, The generation of non-separable artificial earthquake accelerograms for the design of nuclear power plants, Nuclear Engineering and Design 88(1):59-67, 1985. [3] P. Cacciola, A stochastic approach for generating spectrum compatible fully nonstationary earthquakes, Computers & Structures, 88(15-16):889-901, 2010. [4] E.H. Vanmarcke, D.A. Gasparini, Simulated earthquake ground motions. In: Proceedings of the 4th international conference on structural mechanics in reactor technology, K1/9, San Francisco, CA, USA, 1977. [5] P. Cacciola, P. Colajanni, G. Muscolino, Combination of Modal Responses Consistent with Seismic Input Representation, Journal of Structural Engineering 130(1):47-55, 2004.