Shock Fragility Spectra for Equipment Survivability Under Aircraft Impact

Significance 

Infrastructures are susceptible to aircraft impacts, as recent event by the 2001 terrorist attacks on the World Trade Center and the Pentagon. These attacks necessitated the need to urgently develop regulatorily requirements and guidelines for aircraft impact assessments, and specifically, for nuclear power plants. Currently, the basis of standards put in place (by the Nuclear Energy Institute, NEI) for assessing the shock effects of aircraft impact on nuclear facilities are not well understood while the methods and the basis for performing detailed structural analyses for assessing the structural damage are well defined. Moreover, the general information is not available to the public. Technically, the NEI’s guidelines are based on shock damages distances and median fragility limits, which is direction and frequency independent. Despite several studies on the shock damage due to aircraft impact, little has been reported about the frequency-dependent and median-based acceleration fragility.

To this note, a team of researchers organized under the leadership of KEPCO E&C: Mr. Randy James from Structural Solutions Consulting, LLC., Mr. Daniel Parker and Dr. Eric Kjolsing from Structural Integrity Associates, Inc., and Dr. Bong-Rae Kim and Mr. Daejoong Kim from KEPCO Engineering & Construction Company, Inc. developed a median-based fragility spectrum for different equipment categories with the objective of critically assessing the effects of shock due to aircraft impact on the equipment functionality, especially the nuclear facilities. Their work is currently published in ASCE Journal of Structural Engineering.

In their work, the shock fragility spectra were developed in three milestones. First, frequency-dependent median-based fragility spectra limits for different equipment categories were proposed based on the NEI’s guidelines. Second, acceleration time history demands were developed from the proposed shock fragility spectra. It is worth mentioning that the acceleration time history demands on shock propagation due to aircraft impact (obtained from studies) were used as seed functions in the spectral process and as demands in the time history analysis of the representative equipment. Eventually, the researchers also applied the spectrally matched time time-history demands on the representative equipment to analyze and validate the feasibility of the proposed shock fragility spectra in protecting nuclear facilities from aircraft impact effects.

Results showed that the representative equipment could remain functional for the proposed fragility spectra. The verification analysis was conducted in accordance with the structural assessment guidelines provided by the NEI, and the obtained results were consistent with the guidelines. Additionally, the authors observed that the defined capacities of equipment for surviving shock are appropriate for median-based analysis methods and could be assumed to be reasonable representatives of the actual equipment.

In summary, the study findings extend on the NEI’s guidelines fragility limits to frequency-dependent fragility spectra. For all the assessed equipment categories, the representative equipment remained operational for the proposed fragility spectra. In a statement to Advances in Engineering, Dr. Bong-Rae Kim, the corresponding author pointed out the proposed fragility spectra could be effectively used to develop region-specific safe distances as well as provide a detailed assessment of equipment survivability under aircraft impact.

About the author

Bong-Rae Kim

Senior Engineer, Specialist, KEPCO Engineering & Construction Company, Inc.

Bong-Rae Kim received his BS degree in Civil Engineering from Pusan National University, Korea, in 2005 and MS degree in Structural Engineering from Korea Advanced Institute of Science and Technology (KAIST), Korea, in 2006. He received his PhD degree is Structural Engineering from KAIST in 2010 with research on the micromechanics-based progressive damage models for particle and fiber-reinforced composite.

Dr. Kim has worked as a senior engineer in the Department of Civil & Architectural, Environmental Engineering in KEPCO Engineering & Construction Company, Inc. (KEPCO E&C), Korea, since 2011. He is also currently serves as a specialist in the field of special structure in KEPCO E&C. In KEPCO E&C, Dr. Kim has participated in many design projects for nuclear power plant encompassing a broad range of structures (e.g., prestressed concrete structure, reinforced concrete structure, steel structure, and other structure in which they are combined) using the nonlinear static and dynamic analysis, response spectrum and time history analysis of structure, heat transfer – thermal stress interaction analysis, and material failure analysis. In addition, he has carried out the structure integrity assessment of nuclear power plants under the internal or external hazard conditions such as accident pressure and high thermal loading, missile and aircraft impact, and explosion.

His research interests include a nonlinear behavior analysis of concrete and steel structures of nuclear power plant, a structural integrity assessment of nuclear power plant under internal and external accidents, and a structure damage evaluation under high-velocity impact and explosion.

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About the author

Randy J. James

Principal, Structural Solutions Consulting, LLC

Mr. James received a Master of Science degree in Engineering Mechanics from the University of Texas at Austin, Texas, USA, in 1977, and has spent the last 43 years as a practitioner applying mechanics principals and advanced computational methods in solving real world structural engineering problems. Mr. James had a 33-year career with ANATECH Corp in San Diego CA, USA, retiring as President, before opening a consulting firm, Structural Solutions Consulting, LLC, in 2016.

Over the years, Mr. James has tackled many challenging projects encompassing a broad range of applications, including nonlinear dynamics for high-energy impact and seismic loads, soil-structure and fluid-structure interaction, coupled heat transfer and fluid flow, creep and property degradation at elevated temperatures, fatigue life, and fracture mechanics. At ANATECH, he was heavily involved in assessing the performance of steel and reinforced concrete structures, including design verification and retrofits, seismic qualifications, structural reliability and safety, evaluation of impulsive and shock loading, mitigation for heavy load drops, and failure analyses to determine mode of failure and capacity limits under beyond-design-load scenarios. He has performed probabilistic based engineering assessments to better understand and quantify the risks of epistemic and aleatory uncertainties, and in particular for containment systems at nuclear power plants.

Mr. James is internationally recognized for his work in assessing the consequences of aircraft impact, including structural performance and physical damage, shock propagation, and methods for containment of fire spread from pressurized fireballs. This expertise includes methodology development, software validation, application of the methodology on many nuclear plant designs, and interface with various regulatory agencies for acceptance of the results in meeting the regulatory requirements. He was a contributor to the methodology development for assessing structural performance in NEI 07-13, which is an accepted standard for assessing aircraft impact for new nuclear power plant designs, both by the U.S. Nuclear Regulatory Commission and internationally. He also has extensive experience in applying NEI 07-13 methodology and in adapting the core intent of NEI 07-13 for application outside the U. S. and for assessing shock propagation, which is not explicitly covered in NEI 07-13. Mr. James can be reached by email at [email protected] .

Reference

James, R., Parker, D., Kjolsing, E., Kim, B.R., & Kim, D. (2020). Shock Fragility Spectra for Equipment Survivability under Aircraft Impact. ASCE Journal of Structural Engineering, 146(3), 04019211.

Go To ASCE Journal of Structural Engineering

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