Action 6.1 : Response spectra for design and risk calculations

State of the art / Background knowledge

Probabilistic Seismic Hazard Assessments (PSHA) provides Uniform Hazard Spectra (UHS) which define values of spectral accelerations having same exceedance probability. By definition, UHS constitutes an envelope and not a real and single seismic scenario.

Engineering practices lead to commonly use UHS as design spectra with the objective to have reasonable numbers of computations. This approach mostly leads to conservative results as long as site effects are not preponderant.

Fig6 1 1

Figure 1: UHS and deaggregation plots

Limitations of current practice or knowledge (i.e. technological barrier)

UHS as design spectra is therefore not suitable to best-estimate or performance-based seismic analysis. Another way is to use multiple scenarios rather than the UHS in order to obtain more realistic seismic broad band excitations. However, the definition of target spectra that comply with design requirements while being hazard-consistent for a reduced number of structural analyses is not straightforward.

Program of research

The aim is to develop and test alternative methods to the UHS allowing to define design spectra compatible to an industrial context.

Work plan includes 4 main topics:

  1. State of the art of Conditional Mean Spectra (CMS) / Conditional Spectra (CS) methodologies
  2. Implementation of CMS / CS methodology or methodologies selected
  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. To develop a comprehensive methodology that would be feasible in an industrial context.
  5. Guide / Recommendations for generating CMS from a PSHA and on the associated use of the results for nuclear facilities


  • Type: PhD in link with WP5 and Post-doc
  • Collaboration: Pavie University (IUSS), Itlay, IFSTTAR, Paris
  • Status: Not started yet