Effect of multi-component excitation on the sliding response of unanchored components in nuclear facilities

Abstract

During an earthquake, equipment left unanchored in a nuclear facility can slide and interact with safety-critical systems and components, posing a safety risk to the facility. However, computing the response of unanchored components, especially in two directions, can be computationally expensive during the preliminary design stages. Nuclear standards acknowledge this by providing an alternative, approximate method for estimating sliding displacement. This paper investigates the effect of bidirectional horizontal interaction and the influence of the vertical component of excitation on the sliding response of unanchored components. It also evaluates the approximate method in ASCE 4-16 and explores multi-component intensity measures for predicting sliding displacement. A decoupled analysis approach is taken where a suite of 40 floor acceleration histories obtained from response history analysis of a representative nuclear power plant facility are used as input to analyze the response of the sliding components. A Bouc-Wen type model is used to determine the nonlinear sliding response of the unanchored components. The computed responses for the sliding components under uni-, bi-, and tri-axial floor excitation are examined, along with the approximate method, and it is concluded that the approximate method is significantly overconservative in all cases. The influence of the bidirectional interaction and vertical component of acceleration is greatest for sites with high shaking intensity and at higher friction coefficients. Different floor shaking intensity measures are evaluated, and it is found that the most efficient intensity measures are peak floor velocity (PFV) for low friction coefficient values and peak floor acceleration (PFA) for high friction coefficient values; the efficiency of these intensity measures is not significantly affected by incorporating multiple components of excitation.