Colón-Fuentes, Luis A. J.

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    Assessment of directional combination rules for the seismic analysis of nuclear power plant structures
    (2020-07-22) Colón-Fuentes, Luis A. J.; Suárez, Luis E.; College of Engineering; Montejo-Valencia, Luis A.; Vidot-Vega, Aidcer L.; López-Rodríguez, Ricardo R.; Department of Civil Engineering; Huérfano-Moreno, Víctor A.
    To assure the safety of Nuclear Power Plant structures, it is crucial to design them in a way that guarantees the continuous function of systems, structures, and components (SSC) after the seismic event has passed. Seismic analyses considered acceptable by the Nuclear Regulatory Commission (NRC) are mainly divided into time history analyses (THA) and response spectrum analyses (RSA). The RSA methods are based on the square root of the sum of the squares (SRSS) and the 100-40-40 percent rules. These methods provide a fair estimate of critical responses on the structures. However, neither takes directly into consideration for analysis the seismic direction, and if the practicing engineer wishes to do so, the methods must be implemented in a way that multiple time-consuming analyses need to be considered. Currently there are not sufficient studies regarding the importance of seismic directionality on the seismic design and analysis regarding NPPs’ SSCs. For this reason, a method is selected and proposed for consideration. The proposed method is the Complete Quadratic Combination for three components (CQC3), which is a variation of the SRSS that can evaluate the response of a structure at every direction. This permits to visualize the effects imparted on the structure without the need to conduct multiple time-consuming analyses as it would be in the case of a THA or variations of the RSA methods. A comparison between the results obtained with those from RSA methods is presented to show the importance of how, in a real-life scenario, the variation of direction in seismic analysis can highly impact the design of an NPP structure. In this comparison, the benefit of using the CQC3 is discussed. The method’s efficiency and convenience is demonstrated: its formulas for critical angle and critical response do not require much more computations than those needed to apply the common RSA methods, and they produce results for every direction in a single analysis. The results obtained confirm the importance of directional seismic analysis as well as the usefulness of the proposed method.