The goal of this WP is threefold:

• Analysis of spatial variability of surface motion at regional scale (Grenoble basin) and its impact on reliability of infrastructures
• Analysis of the impact of local spatial variability on extended or multi-supported structures
• Development of structural fragility functions order to feed the decision support system of WP4.

Envelope delay to characterize regional variability due to surface waves
In this task we will characterize the envelope delay for selected stations to model the surface wave dispersion characteristics of the Grenoble Basin, from both numerical simulations and recorded motion. Since each station has its own envelope delay, we will provide the frequency-dependent duration lengthening that will vary according to their location on the basin, so we can assess their impact on long period structures. Then, we will pay attention in particular to the effect of near source location and basin edge geometry to the characteristics of the generated surface waves, and how is varying the site-specific envelope delay spectrum as a function to distance from the edge. The impact of surface waves on log-period structures such as tanks will be assessed.

Development of broad band ground motion for transient response analysis
The waveforms developed in WP 2 are limited to an upper frequency of around 5Hz. This is not sufficient to perform soil-structure interaction and conduct transient response analysis for structures with higher eigenmodes. The high-frequency motions will be synthesized using random vibrations theory along with the Specific Barrier Method to model the source in a given tectonic setting. The high-frequency time histories simulated in this manner account for the directivity effects that the fault geometry and rupture progression have on the high-frequency strong motion expected at the given site. A matching filter is then applied to the low and high frequency simulations to avoid overlapping of energy and thus, overestimation of the hazard.

Full FEM soil-structure interaction (SSI) analysis accounting for spatial soil variability
We develop full FEM SSI and SSSI models to assess the impact of local spatial soil variability on structural response of typical nuclear industrial buildings. The stratification of subsoil is accounted for and the spatial variability of the soil modulus is represented by random fields with the characteristics determined in WP 1. Special care will be attached to the definition of the boundary conditions (to keep the meshed soil domain as small as possible) and the definition of the soil properties (linear equivalent approach if possible). Several analysis have to be run, including sampling the random fields, in order to compute response statistics, such as probabilistic in-structure floor response spectra. The results of these analyses will be compared to the simplified approach based sub-structuring where the spatial variability of ground motion is accounted for by a coherency function.

Evaluation of fragility curves for selected structures
We determine detailed fragility curves for the set of structures to be used in the regional loss assessment performed in WP 4. Structural response analysis to assess the impact of spatial variability on structural response and fragility curves of a typical bridge and industrial structures. Comparison of structural vulnerability as a function of location within the basin.