Effect of Multi-Component Excitation on the Sliding Response of Unanchored Components in Nuclear Facilities

Abstract

During an earthquake, unanchored equipment within a nuclear power plant facility can slide and interact with safety-critical systems and components. Previous studies on sliding have largely focused on the response due to unidirectional excitation, as computing the response of unanchored components in three dimensions can be complex and computationally expensive. As such, several prediction equations and a standardized approximate method as outlined in ASCE 4-16 have been developed to estimate the peak sliding displacement. This study investigates the effect of bidirectional horizontal interaction and the influence of vertical excitation on the sliding response of an unanchored object when the x, y, and z, components of earthquake excitation are applied simultaneously. The study also evaluates the approximate method detailed in ASCE 4-16. A suite of 40 floor acceleration histories obtained from response history analysis of a representative nuclear power plant facility are used as input for the sliding model. A wide range of friction coefficients is selected for analysis and the nonlinear sliding response of components is determined through the use of a Bouc-Wen type hysteretic model. Computed responses under uni-, bi- and tri-directional excitation reveal that the effect of bidirectional interaction and vertical excitation is greatest for sites with high shaking intensity. It is also concluded that the ASCE 4-16 approximate method is significantly overconservative in all cases. Additionally, the study expands the concept of multi-component excitation to intensity measures. Twelve intensity measures are selected and evaluated. It is found that most efficient intensity measures vary in efficiency depending on the coefficient of friction, and that the top intensity measures are not significantly affected by incorporating multiple components of excitation.