ASSESSMENT OF RESULTANT EARTHQUAKE IN-STRUCTURE RESPONSE SPECTRA

摘要

Seismic probabilistic risk assessments for nuclear facilities frequently use In-Structure Response Spectra (ISRS) in the calculation of fragilities of systems and components. Typically, horizontal ISRS are calculated along the main directions of seismic analysis, defined as Cartesian axes X and Y. Appreciable differences in these ISRS could arise when the direction of X and Y changes either for the seismic input or the local ISRS. It is impractical to repeat the analyses for all anticipated directions of ground motion and of equipment orientation. Thus, aiming to reduce the impact of a particular selection of X-Y axes, the authors have proposed the calculation of resultant horizontal In-Structure Response Spectra. These spectra are practically insensitive to the choice of X-Y axes. This paper describes confirmatory analyses of the "invariance" property of resultant ISRS. In addition, we contrast conventional and resultant ISRS calculated with stick and with finite element models of the same structure. It is found that the agreement between resultant ISRS from the two models is significantly more favourable than for ISRS oriented along X and Y. Therefore, resultant ISRS provide more robust estimates of seismic demand when somewhat less refined models are used in the analyses.