Title

Methodologies to improve the ground motion description and the selection process of times histories for seismic analysis of nuclear power plants.

Academic partnership

IMSIA: Institut des sciences de la mécanique et applications industrielles, Pavia University (IUSS), IFSTTAR.

EDF supervisors: EDF R&D (G. Senfaute, I. Zentner, G. Deveza) EDF DT (J. Berger, M. Caudron, E. Viallet).

Work place: EDF R&D, Paris Saclay
Starting date: February 2019
Duration: 18 months

Objective

The aim is to implement methodologies to improve the ground motion description and selection process of sets of times histories to be used for seismic analysis of the nuclear industry in France. This research has to produce concrete recommendations to improve the engineering practices. The research program would organised in two main steps: 1) Process of selection or generation of times histories 2) Evaluation of response spectra for design and risk calculation.

This research concerns activities 6.1 and 6.2 (WP6) of SIGMA21 research program

Technical program description

Step 1: Process of selection or generation of times histories

Objectives:

  • To provide tools to Engineers for the selection of sets of time histories. This process would rely on criteria that are “induced damage driven” in order to make sure that any selected set of time histories, whatever its origin, would lead to realistic damages (median, body and range) to structures and equipment.
  • To demonstrate that if the same effort is put on the selection of the time histories (modified natural or synthetic), then the use of synthetic time histories leads to the same level of quality in terms of damages to structures and this even for non-linear studies as natural times histories.

Work program:

    • To develop, in code_aster, a set of Simple Non-Linear Oscillators (SNLO), including different types of non-linear behavior. The objective is to cover all main types of non-linear behavior that could be observed on NPP sites (including soil, structures and equipment). For this purpose:

 

    • SNLO can be inspired from Humber et al. (2014) and Viallet et al. (2017),

 

    • Other SNLO could be developed or selected through literature review,

To perform extensive calculations of damages induced by real earthquakes directly coming from Strong Motion DataBase (SMDB). The objective is to calculate damage induced by real earthquakes (as recorded) on a wide range of types of SNLO, from a large number of time-histories. Two main tasks have to be conducted:

    • Perform statistical assessments of the results obtained from different SMDB, including median body and range,
    • Propose and establish Damage Prediction Equation (DMPEs) for each considered SMDB
  • To select sets of time histories from different methods and based on different criteria used by engineers or available in the literature and performing calculations of damages on SNLO. The objective is to assess current practice in selecting or generating time histories in term of damage induced on SNLO, from a large number of time-histories, main works:
    • Review of available current practices in selection or generation of time histories,
    • Selection or generation of different sets of time histories from available practices, and from different kinds of earthquakes (different targets such as: far field, near field, low magnitude, high magnitude …) and calculate damage induced on SNLO, from a large number of time-histories,
    • Perform statistical analyses of the results obtained from these different cases, including median estimates, body and range.
  • To evaluate significant criteria for the selection or generation of time histories by comparison with the recorded data in the SMDB, based on induced damage. The objective is to perform an extensive comparison of the damage induced by real earthquakes to the damaged estimated based on current engineering practice to assess the representativeness of induced damage, the comparison should include median, body and range, and also the size of the sample (number of time histories)
  • To give conclusions and recommendations for engineering practice. The objective is to produce a guide with recommendation that would improve current engineering practice:
    • This should include generation or selection criteria considering the induced damage as the key target representativeness criteria
    • Considering that other ground motion parameters than PGA could be better appropriated, eg. Pseudo spectral acceleration PSA (CAV, Arias Intensity, Strong motion duration …)
    • Including recommendations regarding median estimations and variability considerations

Synthesis of work plan:

  1. Development of Simple Non-Linear Oscillators (SNLO) in Code-Aster, including different types of typical non-linear behaviors,
  2. Performing extensive calculations of damages induced by real earthquakes directly coming from Strong Motion Data Bases (SMDB) on these SNLO,
  3. Selection of sets of time histories from different methods and based on different criteria and performing calculations of damages based on these SNLO,
  4. Evaluation of the criteria of relevance for the selection or generation of time histories by comparison with ones from SMDB, based on induced damage representativeness,
  5. Elaborate a guide with clear recommendations for engineering practice

Set 2: Response spectra for design

This work is associated to research conducted in the framework of a PhD theses that will start in January 2019 and that is included in WP5 of SIGMA2 project, see in annex the work program and organization. The present research will participate in the second phase of the PhD thesis to elaborate a guide with recommendation useful for engineering practices.

Objective of the PhD thesis
The aim is to develop and test alternative methods to the UHS allowing to define design spectra that could be used in an industrial context. The work plan includes 4 main topics:

  1. State of the art of Conditional Mean Spectra (CMS) / Conditional Spectra (CS) methodologies.
  2. To develop and implement a comprehensive methodology that would be feasible in an industrial context.
  3. Application of CMS / CS methodology in a pilot site (have to be defined), including a comparative study with other more classical method (UHS, decomposition of UHS by others methods…).
  4. Guide / Recommendations for generating CMS from a PSHA and on the associated use of the results for nuclear facilities.

The Postdoc will participate actively in the realisation of the tasks 3 and 4 in a complementary work with the PhD. The main objective of the Postdoc is to contribute to the task 4 regarding the elaboration of guide with recommendation for generating CMS from a PSHA and on the associated use of the results for nuclear facilities.

Contact:
Gloria SENFAUTE
Tel + 33 1 78 19 19 34 33
Gloria.senfaute@edf.fr

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