- 1 - Modeling and Analysis for Seismic Evaluation of Nuclear Structures S.A. Short, 1 O. Gurbuz 2 , A.S. Whittaker 3 , and M. Shams 4 1 Simpson Gumpertz & Heger, 4000 MacArthur Blvd, Suite 710, Newport Beach, CA, 92660; PH (949) 930-2159; email: sashort@sgh.com 2 Gurbuz Consulting, 16162 Tortola Circle, Huntington Beach, CA, 92649; PH (714) 625-0656; email: ogurbuz@verizon.net 3 University of Buffalo, State University of New York, Red Jacket Quadrangle, Buffalo, NY, 14261; PH (716) 645-4364; email: awhittak@buffalo.edu 4 United States Nuclear Regulatory Commission, 11555 Rockville Pike, Rockville, MD 20852; PH (301) 415-0501; email: mohamed.shams@nrc.gov ABSTRACT Nuclear structures are typically reinforced concrete shear wall buildings constructed either embedded in or on the ground surface. Nuclear structures contain equipment, systems, and components that are safety-related and generally require seismic qualification by either full-scale testing or analysis. Evaluation of a safety-related nuclear structure is typically performed by dynamic analysis of a finite element model of the structure considering three orthogonal components of input motion. The paper addresses updates to ASCE 4 in the areas of finite element modeling, damping for multiple levels of response, modal response combination, frequency domain response methods, multi-step analyses, and nonlinear seismic analysis. MODELING OF STRUCTURES General Requirements. The arrangements of nuclear plant buildings and major components are structurally complex, and the development of mathematical models for seismic effects requires careful consideration. The amount of detail used to represent a structure in a mathematical model depends on the structural configuration and the use of the model. Specific considerations and requirements pertinent to idealizing complex plant structures are provided in the standard. The seismic response of a structure shall be determined by preparing a mathematical model of the structure and calculating the response of the model to the prescribed seismic input. Mass and stiffness distribution in the structure shall be appropriately included. The mathematical model shall represent, at a minimum, the structural elements that form the primary load resisting system of the structure. The hydrodynamic effects of any significant water mass interacting with the structure shall be considered in modeling the inertial characteristics. The response parameter(s) of interest shall be identified. Response parameter(s) of interest are defined as the desired results of a specific analysis that will be used in design and/or evaluations. Different structural models are often developed for different purposes and the purpose of each model should be clearly identified.