Floor response characteristics of NPP auxiliary building subjected to bi-directional ground motions

The objective of this study is to investigate the seismic floor response characteristics at critical locations of the auxiliary building (AB) of a nuclear power plant. AB is so irregular that floor responses at different locations are expected to be different even at the same floor. Time history analyses are performed for a finite element model of AB for various bi-directional ground motions. It is observed that floor response spectra at 12 distinct locations are significantly different. The bi-directional effect is observed to be 24 %–42 % higher when compared to uni-directional cases. The response trajectory due to bi-directional motions shows the major direction of response are variable and solely depends on the ground motion properties suggesting the current analysis techniques being viable for over/under estimation of floor responses. The critical angle of incidence for AB is found to be 105°. Hence, this study also suggests virtually dividing a floor into several groups based on their seismic response characteristics for an efficient evaluation of the seismic performance of large structures like AB.