Application of cross-oscillator, cross-floor response spectrum method of multiply supported systems, considering the correlations between three directional earthquake excitations

Response spectrum analysis method is widely used for the seismic design of equipment and piping systems of nuclear power plant, or other industrial facilities. Some of the equipment and piping systems are multiply supported with plural floors, or several different points. In these cases, conservative design methods, such as uniform response spectrum (URS) method that envelopes all of the individual response spectra, or independent support motion (ISM) method are commonly accepted. These design methods are not practical, but often mislead to design with unnecessary conservatism. This paper presents the practical seismic analysis methodologies considering the correlation coefficients of seismic responses with multi-directional excitations, which is extended to apply the correlations between modal responses and between support motions, called cross-oscillator, cross-floor response spectrum by Asfura, A. and Kiureghian, A,D., and numerical examples are also presented to examine the validity for the seismic analysis method of multiply supported secondary systems, with simultaneous three directional excitations of each X, Y, Z axis.