Evaluation of seismic hazard for the assessment of historical elements at risk : description of input and selection of intensity measures

The assessment of historical elements at risk from earthquake loading presents a number of differences from the seismic evaluation of modern structures, for design or retrofitting purposes, which is covered by existing building codes, and for the development of fragility curves, procedures for which have been extensively developed in the past decade. This article briefly discusses: the hazard framework for historical assets, including a consideration of the appropriate return period to be used for such elements at risk; the intensity measures that could be used to describe earthquake shaking for the analysis of historical assets; and available approaches for their assessment. We then discuss various unique aspects of historical assets that mean the characterisation of earthquake loading must be different from that for modern structures. For example, historical buildings are often composed of heterogeneous materials (e.g., old masonry) and they are sometimes located where strong local site effects occur due to: steep topography (e.g., hilltops), basin effects or foundations built on the remains of previous structures. Standard seismic hazard assessment undertaken for modern structures and the majority of sites is generally not appropriate. Within the PERPETUATE project performance-based assessments, using nonlinear static and dynamic analyses for the evaluation of structural response of historical assets, were undertaken. The steps outlined in this article are important for input to these assessments

Nonlinear numerical method for earthquake site response analysis I — elastoplastic cyclic model and parameter identification strategy

This paper, along with its companion paper, presents the importance of the adequate soil behaviour model to simulate earthquake site response analysis. An elastoplastic model taking into account the elementary necessary plastic mechanisms such as progressive friction mobilization, Coulomb type failure, critical state and dilatancy/contractance flow rule, is used. However, one of the obstacles in the use of elastoplasticmodels in the everyday design processes for evaluation of the seismic soil response is the difficulty in identifying their parameters. In this paper, a methodology to identify a coherent set of parameters of the elastoplastic model for a given type of soil is presented. The strategy behind the decision making process proposed here is based on the use of minimum physical and easily measurable properties of the soil to directly provide or indirectly assess the required model parameters

Quantitative seismic hazard assessment

International audienceWe analyze the ingredients required for deterministic wave propagation simulation in order to estimate more accurately ground motion in terms of amplitude, frequency content and duration. Building maps of expected ground motion before a catastrophic event for various scenarios may help design ways to mitigate impacts of ground vibrations as well as fast calibration of these maps once the event occurs. Reconstruction of 3D structures requires collection of information at two different scales: the regional one (a few tens of kilometres) and the local (a few tens of metres to hundreds of metres). Different techniques from permanent to temporary deployments of seismic stations and from active to passive source excitations together with other geophysical and geotechnical investigations will provide the necessary information. Characterisation of possible seismic sources is another challenge and requires careful seismotectonic analysis in the region of interest. Uncertainties may be large provided that one can reproduce wave propagation from these hypothetical spatially extended sources. Frequency content of these simulations is more limited by our knowledge of the medium than by computer resources. In fact, in order to perform such simulations, the geological structure has to be known within a resolution scale of one-tenth of the wavelength. Duration and amplitude are affected by the source mechanism and the mechanical properties of the underground structure. Variability in these ground motion estimations should be appreciated and key parameters identified. Designing approaches to calibrate these simulations with recorded data as well as necessary links with the probabilistic approach should be addressed in the future

Coupling of FDM and FEM in seismic wave propagation

International audienceA specific approach is studied to couple two well-known numerical methods, a finite difference method (FDM) and a finite element method (FEM) for simulating regional seismic wave propagation to local site response. This coupling uses a technique of the “paraxial approximation” in order to input in the FEM the seismic wave generated in the FDM. The main advantage of this approach is to locally extract an area of interest where non-linear soil response or complex geometry is important from the regional wave propagation in a relatively simple medium. This result in taking advantage of both methods: the portability of the FDM and the flexibility of the FEM. This paper presents a theoretical framework of the paraxial approximation, through which the coupling is realized between the FDM and the FEM, and demonstrates some examples for the validation of the proposed coupling technique as well as its possible applications

Some insights on dynamic rupture modelling using a finite element method

International audienceFinite element methods (FEM), as often used in soil dynamics should be a powerful tool to simulate the dynamic rupture process on earthquake faults, allowing us to take into account the asymmetry of fault geometry with respect to the ground surface as well as material heterogeneity with inelastic properties. A FEM program to model non-linear elastodynamics, GEFDYN, is used to model rupture propagation on a seismic fault. The fault is simulated using "joint-elements" that are thin and flat and may be programmed to simulate a number of frictional properties. We perform preliminary simulations on a single plane fault embedded in a 2D homogeneous unbounded elastic media and compare results with those of a boundary integral equation method. Under uniform initial stress conditions, we release certain amount of stress on a small area of the fault and the dynamic rupture progresses spontaneously controlled by the plastic behaviour of joint-elements used to simulate the Coulomb friction law on the fault. The formulation of the joint elements, as well as the parameters of their constitutive model are analysed and discussed, such as the shear elastic modulus Gjoint. We find it important to carefully treat these joint-elements to obtain the accurate solutions. With these tests, we demonstrate that this tool constitutes an appropriate model to study dynamic rupture propagation on a fault

Modelisation numerique de la propagation des ondes dans les milieux poreux anelastiques

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Le risque sismique en France

National audienc