Fundamental Study on Probabilistic Evaluation of Earthquake Load

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Many aspects for the probabilistic estimation on the erathquake response have been considered. At first an improved seismic hazard analysis is proposed by the use of an isolated model of earthquake occuring on plate boundaries and by assuming appropriate upper boundary of maximum velocity for the earthquake ground motion. Generation methods of the critical input wave for dynamic responses are developed for various types of models. For origine oriented hysteresis models linear phase properties to the frequency components are used and for normal bi-linear hystresis models a phase property which causes large values of the time history with equally spaced time interval is used. The distoribution function of the sum of two log-normal variables is approximated by a log-normal distribution with proposed parameters. The accuracy of the approximation is examined by the Monte-Carlo method for some check points. It is recognized by micro-tremore measurements that the natural frequency of existing buildings is shorter and the damping ratio is less for higher modes than those used at the design. Parameters on dynamic properties of tall buildings, i.e.the mass-stiffness ratio and the yield shear force coefficient and so on, are examined statistically. Representative dynamic models are demonstrated by 6 models for S structures and 5 for RC structeres by considering distributions of these parameters to the hight. Reliability indeces for the seismic safety of those models are revealed as between 2 and 3. Design peak ground acceleration is proposed with the appropriate safety degree based on the optimum reliability due to minimum total cost concept. The relation among those results summarized here is also reviewed.