Response of base-isolated nuclear structures for design and beyond- design basis earthquake shaking Yin-Nan Huang 1, * ,† , Andrew S. Whittaker 2 , Robert P. Kennedy 3 and Ronald L. Mayes 4 1 Department of Civil Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617, Taiwan 2 Department of Civil, Structural and Environmental Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USA 3 RPK Structural Mechanics Consulting Inc., Escondido, CA 92026, USA 4 Simpson Gumpertz & Heger Inc., San Francisco, CA 94105, USA SUMMARY The American Society of Civil Engineers (ASCE) 43-05 presents two performance objectives for the design of nuclear structures, systems and components in nuclear facilities: (1) 1% probability of unacceptable perfor- mance for 100% design basis earthquake (DBE) shaking and (2) 10% probability of unacceptable performance for 150% DBE shaking. To aid in the revision of the ASCE 4-98 procedures for the analysis and design of base-isolated nuclear power plants and meet the intent of ASCE 43-05, a series of nonlinear response-history analyses was performed to study the impact of the variability in both earthquake ground motion and mechanical properties of isolation systems on the seismic responses of base-isolated nuclear power plants. Computations were performed for three representative sites (rock and soil sites in the Central and Eastern United States and a rock site in the Western United States) and three types of isolators (lead rubber, Friction Pendulum and low-damping rubber bearings) using realistic mechanical properties for the isolators. Estimates were made of (1) the ratio of the 99th percentile (90th percentile) response of isolation systems computed using a distribution of spectral demands and distributions of isolator mechanical properties to the median response of isolation systems computed using best-estimate properties and 100% (150%) spectrum-compatible DBE ground motions; (2) the number of sets of three-component ground motions to be used for response-history analysis to develop a reliable estimate of the median response of isolation systems. The results of this study provide the technical basis for the revision of ASCE Standard 4-98. Copyright © 2012 John Wiley & Sons, Ltd. Received 20 February 2012; Revised 24 April 2012; Accepted 1 May 2012 KEY WORDS: nuclear power plant; base isolation; design basis earthquake; rubber bearing; Friction Pendulum 1. INTRODUCTION Base isolation has been used to protect buildings, bridges and mission-critical infrastructure from the damaging effects of earthquake shaking [1, 2]. It has been implemented in safety-related nuclear structures in France and South Africa [3]. In the United States, there are no applications of seismic isolation to nuclear structures at the time of this writing although some vendors of Nuclear Steam Supply Systems and power utilities are considering seismic isolation for new build plants. Seismic isolation systems worthy of consideration for application to nuclear facilities in North America include two types of elastomeric bearings and one type of sliding bearing. Lead–rubber (LR) and low-damping rubber (LDR) bearings are examples of elastomeric bearings. The sliding bearing that is suitable for application to nuclear structures is the Friction Pendulum (FP) (Earthquake Protection *Correspondence to: Yin-Nan Huang, Department of Civil Engineering, National Taiwan University, Taiwan; Address: No. 1, Sec. 4, Roosevelt Road, Taipei, 10617 Taiwan. † E-mail: ynhuang@ntu.edu.tw Copyright © 2012 John Wiley & Sons, Ltd. EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS Earthquake Engng Struct. Dyn. 2012 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/eqe.2209