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Furinghetti M.,EUCENTRE | Pavese A.,University of Pavia
Mechanics Based Design of Structures and Machines | Year: 2017

Concave surface slider (CSS) devices represent an effective solution for base-isolation design problems. In such isolators the energy dissipation capability is induced by the sliding motions which occur at one or more sliding interfaces. The spherical shape of the sliding surfaces provides a significant recentering behavior, by means of the stepwise projection of the applied vertical load with respect to both horizontal directions. For two-components earthquake excitations, the recentering force is computed as a linear spring with respect to displacements along the main directions of motion; whereas, the frictional response is returned by the stepwise projection of the total frictional force, which is aligned with respect to the trajectory of the device: thus, a bi-axial interaction of the directions of motion has to be accounted for, when a friction-based device is modelled. However, available commercial software which can capture such a behavior are limited. In this work an analytical procedure is defined, for the computation of an “equivalent uniaxial accelerogram” for the seismic assessment of a base-isolated structure, subjected to a bi-directional earthquake. Thanks to the proposed theory, it is possible to compute a single ground acceleration time-history, related to a proper direction angle, which can reproduce the same effects of a two-components seismic event on a base-isolated structural system: the analogy between the equivalent uniaxial and the bi-directional events has been studied in terms of acceleration, velocity and displacement spectra respectively. Results for the base-isolated structure have been analyzed in terms of displacement, absolute acceleration and interstorey shear responses. © 2017 Taylor & Francis

Bommer J.J.,Imperial College London | Crowley H.,EUCENTRE
Seismological Research Letters | Year: 2017

A lower limit of magnitude Mmin is routinely defined for integrations of earthquake scenarios in probabilistic seismic-hazard analysis but there is widespread misunderstanding of the technical bases for determining the value of this parameter. In this article, several misconceptions are identified and discarded prior to providing a clear and unambiguous definition of Mmin that points to the fact that seismic-hazard assessment is always conditioned by the intended application of the outputs. We argue that Mmin is therefore an engineering parameter that is ultimately related to seismic risk rather than seismic hazard. The confusion surrounding this topic could be largely alleviated by defining lower limits on appropriate intensity measures rather than on magnitudes used as a proxy for shaking levels.

Scandella L.,EUCENTRE | Paolucci R.,Polytechnic of Milan
Bulletin of Earthquake Engineering | Year: 2010

Transient ground strains are recognized to govern the response of buried elongated structures, such as pipelines and tunnels, under seismic wave propagation. Since a direct measure of ground strains is not generally available, simplified formulas relating peak ground strain to peak ground velocity, and based on 1D wave propagation theory in homogeneous media, are typically used for seismic design. Although they are adopted by most of the available technical guidelines, the use of these formulas may be questionable in complex realistic situations as either in the presence of strong lateral discontinuities, or in the epicentral area of large earthquakes, or in sites where relevant site amplification effects and spatial incoherency of ground motion are expected. To provide a contribution to overcome the previous limitations, a simplified formula relating peak ground longitudinal strain to peak ground velocity is proposed in this paper, as a function of the geometrical and dynamic parameters which have the major influence on strain evaluation. The formula has been obtained under small-strain assumptions, so that it can reasonably be applied under linear or moderately non-linear soil behaviour. The adequacy of this formula in the most common case of vertically propagating S-waves has been checked against 2D numerical solutions by Spectral Elements (SE) for representative geological cross-sections in Parkway Valley (New Zealand) and in the cities of Catania (Italy) and Thessaloniki (Greece). The shear strain and the longitudinal strain variability with depth is also investigated, through some qualitative examples and comparisons with analytical formulas. © 2010 Springer Science+Business Media B.V.

Bal I.E.,EUCENTRE | Bommer J.J.,Imperial College London | Stafford P.J.,Imperial College London | Crowley H.,GEM Foundation | Pinho R.,GEM Foundation
Earthquake Spectra | Year: 2010

Exposure data available to developers of earthquake loss models are often very crudely aggregated spatially, and in such cases very considerable effort can be required to refine the geographical resolution of the building stock inventory. The influence of the geographical resolution of the exposure data for the Sea of Marmara region in Turkey is explored using several different levels of spatial aggregation to estimate the losses due to a single earthquake scenario. The results show that the total damage over an urban area, expressed as a mean damage ratio (MDR), is rather insensitive to the spatial resolution of the exposure data if a sufficiently large number of ground-motion simulations are used. However, the variability of the MDR estimates does reduce as the spatial resolution becomes higher, reducing the number of simulations required, although there appears to be a law of diminishing returns in going to very high exposure data resolution. This is largely due to the inherent and irreducible spatial variability of ground motion, which suggests that if only mean MDR estimates are needed, the effort required to refine the spatial definition of exposure data is not justified. © 2010, Earthquake Engineering Research Institute.

Beyer K.,Ecole Polytechnique Federale de Lausanne | Beyer K.,ETH Zurich | Dazio A.,EUCENTRE | Dazio A.,ETH Zurich
Earthquake Spectra | Year: 2012

This paper presents the results of an experimental campaign on masonry spandrels. Within this campaign, four masonry spandrels were subjected to quasi-static cyclic loading. Two different spandrel configurations were tested. The first configuration comprised a masonry spandrel with a timber lintel, and the second configuration, a masonry spandrel on a shallow masonry arch. For each configuration, two specimens were tested. The first was tested with a constant axial load in the spandrel, while for the second specimen, the axial load in the spandrel depended on the axial elongation of the spandrel. This paper summarizes the properties of the four test units, the test setup, and the most important results from the experiments, documenting the failure mechanisms that developed and the force-deformation hysteresis of the spandrel elements. The paper also presents a mechanical model for estimating the peak strength of masonry spandrels. © 2012, Earthquake Engineering Research Institute.

Pessina V.,Italian National Institute of Geophysics and Volcanology | Fiorini E.,EUCENTRE
Soil Dynamics and Earthquake Engineering | Year: 2014

Morphometric analyses of high resolution digital elevation models (DEM), with the support of Geographic Information Systems (GIS), have been implemented to provide a practical tool for the identification on a large scale of sites where, according to the EC8 prescriptions, a topography amplification is expected. An ad hoc procedure for the hilltop ridge detection was implemented to be used in the morphological characterization, together with the standard GIS sequence of steps. The proposed method allowed the fast classification of more than 800 seismic recording stations located on the Alps and the Apennine, according to the indications of the current European norm and the Italian seismic code. The aim is to improve the characterization of the stations of seismic archives, in the view of a potential cross-checking of observed amplification with the attributed site class category. © 2014 Elsevier Ltd.

Silva V.,University of Aveiro | Crowley H.,EUCENTRE | Varum H.,University of Aveiro | Pinho R.,University of Pavia | Sousa R.,ROSE Programme
Earthquake Engineering and Structural Dynamics | Year: 2014

The recognition of fragility and vulnerability functions as a fundamental tool in seismic risk assessment has led to the development of more and more complex and elaborate procedures for their computation. Although these functions have been traditionally produced using observed damage and loss data, more recent studies propose the employment of analytical methodologies as a way to overcome the frequent lack of post-earthquake data. The variation of the structural modelling approach on the estimation of building capacity has been the target of many studies in the past; however, its influence on the resulting vulnerability model for classes of buildings, the impact in loss estimations or propagation of the uncertainty to the seismic risk calculations has so far been the object of limited scrutiny. In this paper, an extensive study of static and dynamic procedures for estimating the nonlinear response of buildings has been carried out to evaluate the impact of the chosen methodology on the resulting capacity, fragility, vulnerability and risk outputs. Moreover, the computational effort and numerical stability provided by each approach have been evaluated and conclusions drawn regarding the optimal balance between accuracy and complexity. © 2013 John Wiley & Sons, Ltd.

Silva V.,University of Aveiro | Crowley H.,EUCENTRE | Pinho R.,University of Pavia | Varum H.,University of Aveiro
Engineering Structures | Year: 2013

This paper presents a new procedure to derive fragility functions for populations of buildings that relies on the displacement-based earthquake loss assessment (DBELA) methodology. The recent developments in this methodology are also presented herein, such as the development of new formulae for the calculation of the yield period or the consideration of infilled frame structures. In the fragility method proposed herein, thousands of synthetic buildings have been produced considering probabilistic distributions describing the variability in their geometrical and material properties. Then, their nonlinear capacity has been estimated using the DBELA method and their performance against a large set of ground motion records has been calculated. Global limit states are used to estimate the distribution of buildings in each damage state for different levels of ground motion, and a regression algorithm is applied to derive fragility functions for each limit state. The proposed methodology is demonstrated for the case of ductile and non-ductile Turkish reinforced concrete buildings with and without masonry infill walls, and compared with results obtained using nonlinear dynamic procedures and with the results from previous studies. © 2013 Elsevier Ltd.

Bommer J.J.,Imperial College London | Crowley H.,Eucentre | Pinho R.,University of Pavia
Journal of Seismology | Year: 2015

Earthquakes may be induced by a wide range of anthropogenic activities such as mining, fluid injection and extraction, and hydraulic fracturing. In recent years, the increased occurrence of induced seismicity and the impact of some of these earthquakes on the built environment have heightened both public concern and regulatory scrutiny, motivating the need for a framework for the management of induced seismicity. Efforts to develop systems to enable control of seismicity have not yet resulted in solutions that can be applied with confidence in most cases. The more rational approach proposed herein is based on applying the same risk quantification and mitigation measures that are applied to the hazard from natural seismicity. This framework allows informed decision-making regarding the conduct of anthropogenic activities that may cause earthquakes. The consequent risk, if related to non-structural damage (when re-location is not an option), can be addressed by appropriate financial compensation. If the risk poses a threat to life and limb, then it may be reduced through the application of strengthening measures in the built environment—the cost of which can be balanced against the economic benefits of the activity in question—rather than attempting to ensure that some threshold on earthquake magnitude or ground-shaking amplitude is not exceeded. However, because of the specific characteristics of induced earthquakes—which may occur in regions with little or no natural seismicity—the procedures used in standard earthquake engineering need adaptation and modification for application to induced seismicity. © 2015, The Author(s).

Nascimbene R.,EUCENTRE
Wind and Structures, An International Journal | Year: 2013

The aim of the paper is to use optimization and advanced numerical computation of a sail fiber-reinforced composite model to increase the performance of a yacht under wind action. Designing a composite-shell system against the wind is a very complex problem, which only in the last two decades has been approached by advanced modeling, optimization and computer fluid dynamics (CFDs) based methods. A sail is a tensile structure hoisted on the rig of a yacht, inflated by wind pressure. Our objective is the multiple criteria optimization of a sail, the engine of a yacht, in order to obtain the maximum thrust force for a given load distribution. We will compute the best possible yarn thickness orientation and distribution in order to minimize the total fiber volume with some displacement constraints and in order to leave the most uniform stress distribution over the whole structure. In this paper our attention will be focused on computer simulation, modeling and optimization of a sail-shape mathematical model in different regatta and wind conditions, with the purpose of improving maneuverability and speed made good. © 2013 Techno-Press, Ltd.

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