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Earthquake early warning for earth dams
No full textThe paper outlines the basic concepts of an Earthquake Early Warning (EEW) system applied to earth dams. Past experience indicates that vulnerability of earth dams is generally low under both static and seismic loading conditions. In spite of this, a high risk level is associated to dams because of their high exposure factor. Soon after a strong earthquake, the authorities in charge of earth dam safety act completely unprepared to face the emergency, due to the lack of pre-arranged predictive/interpretative tools. This highlights the need for automated systems suitable to convert monitoring data in dam safety assessment. Nowadays the application of early warning systems to dams is fully supported by the technological progress achieved in the telecommunication field, since it is possible to install and automate recordings and transmission of all physical variables significant to check dam safety. However, a considerable lack still arises in the predictive models for interpreting monitoring data and providing indicators on dam safety soon after an earthquake. © The authors and ICE Publishing: All rights reserved, 201
A simplified approach to account for through-soil interaction between two adjacent shallow foundations
No full textNeighbouring buildings, even though disconnected from the structural viewpoint, may interact through the underlying soil especially when they are founded on very soft soils. Despite some pioneering studies since the early 1970’s, structure–soil–structure interaction has yet to be further investigated to reveal the effects that could be exerted on both the static and dynamic response of nearby structures. The present work aims at expanding the theoretical knowledge on this phenomenon through an extensive parametric study based on a truly 3D continuum approach solved through the Flac3D finite difference software. The impedance functions of two closely-spaced shallow foundations have been numerically calculated by varying the distance between the nearby footings and the subsoil configuration (homogeneous or layered). The numerical results have elucidated important effects of cross interaction between two neighbouring foundations. The static stiffness reduces, and this effect is increasingly significant as the foundations are closer whatever the subsoil conditions are. The dynamic coefficients increase with respect to those corresponding to the single footing over halfspace. Such effect is less important for the layer-over-halfspace soil configuration, for which the dynamic coefficients are mainly affected by the frequency response of the stratum. Finally, in the realm of the sub-structure approach, a novel simplified design approach, based on group factors for closely-spaced shallow foundations, was proposed to compute the soil-foundation impedance matrix englobing the foundation–foundation interaction in addition to the soil–foundation interaction
Prove in sito sulla diga del Camastra: tecniche sperimentali e risultati
No full textL’articolo illustra le tecniche sperimentali e i risultati di prove in sito eseguite per la caratterizzazione meccanica dei materiali costituenti la diga del Camastra, realizzata in provincia di Potenza negli anni ‘60. Le prove eseguite, non convezionali per una diga in terra, consistono in misure SASW, Down Hole (DH) e dilatometriche (DMT). Le misure SASW fanno riferimento a tre stendimenti, rispettivamente collocati lungo il coronamento, una banchina intermedia e la base della diga. Le prove Down Hole e DMT, realizzate mediante il dilatometro sismico, fanno riferimento a quattro verticali ubicate in asse al nucleo. Le prove, collocate nel più ampio ambito delle verifiche di controllo della sicurezza dell’opera in regime statico e sismico, sono state realizzate per misurare parametri di tipo tradizionale, come la coesione non drenata del nucleo, per determinare la variazione del modulo di rigidezza a taglio con il livello dicdeformazione e, infine, per realizzare il controllo semi-qualitativo delle proprietà meccaniche del nucleo. Nell’articolo sono discussi criticamente i risultati delle prove SASW, riferite convenzionalmente alla verticale passante per il baricentro di ciascuno stendimento. Sono inoltre rappresentati e discussi i risultati delle quattro prove DH, confrontando tra loro le diverse distribuzioni ottenute nel nucleo ed estendendo poi il confronto ai risultati ottenuti dalle due diverse metodologie di prova. La fase interpretativa dei risultati richiede a vari livelli la conoscenza dello stato tensionale efficace che, nel caso di una diga, non è derivabile in base alle semplici relazioni valide per le condizioni litostatiche con piano di campagna orizzontale ed acqua ferma. Nell’articolo sono pertanto riportate le procedure adottate in queste particolari condizioni di prova. L’articolo è concluso da alcune considerazioni sull’efficacia delle varie prove nella caratterizzazione meccanica e idraulica dei materiali costituenti una diga in terra
A STEP INTO THE DEFINITION OF THE SEISMIC RISK FOR THE CITY OF BENEVENTO (ITALY)
Full text linkThis paper gives a contribution in the definition of the seismic hazard for the city of Benevento in Southern Italy, from a geotechnical engineering viewpoint. To pursue this goal, an extensive geotechnical characterization of the city subsoil was achieved collecting data available at the Department of Geotechnical Engineering (DIG), University of Napoli and Benevento municipal technical office. A quantitative definition of all soil parameters needed for seismic response analyses has been achieved in 19 verticals. These verticals were selected because seismic shear wave velocities were available.
Attention was paid in defining strain dependent shear stiffness and damping ratio for the geomaterials present in the urban area. A new method to correct the Masing criteria was adopted, when associated to Ramberg-Osgood model. This methodology consists in adding an initial damping factor to the damping-shear strain curve and in adopting an empirical factor to correct the area loop of the curve to match experimental data. The corrective value was deduced by interpreting the relationship existing between several G() and D() curves obtained from RCTS tests performed at the DIG, on both natural and artificial soils. A value of equal to 0.8 was suitable to match the experimental damping-shear strain curves.
The seismic hazard in the city was evaluated on the basis of two seismic scenarios, respectively characterized by high and low acceleration levels. The first one is representative for Sannio 1688 earthquake (PGA = 0.38g at bedrock). The second seismic scenario is aimed at simulating the effect of the 11/23/1980 Irpinia earthquake in the city of Benevento (PGA= 0.03g at bedrock).
Seismic analyses were conducted first by using simplified approaches, such as the site classification suggested by the Eurocode 8, then considering 1-D layered visco-elastic subsoil, behaving linearly and successively adding non-linearity.
According to the EuroCode8 guidelines in the whole urban area of Benevento site effects are not relevant, since an almost homogeneous distribution of acceleration response spectra was obtained.
With the non linear analyses the zonation map of the city of Benevento was sketched grouping together the response spectra having similar features. From the two seismic scenarios, it clearly emerges the influence of the input motion variability on the results of a seismic zonation.
Since Integral parameters such as the Arias intensity or the rms acceleration, are representative of the energy content of a seismic signal, the Arias Intensity at ground level, normalized to the value pertaining to the input motion, was mapped for the two seismic scenarios. It was observed that the areal distribution of this parameter approximately matches that depicted on the base of response spectra
Effetto della componente verticale del moto sismico sulla risposta di una diga in terra zonata attraverso approcci semplificati e avanzati
No full textNelle analisi dinamiche di dighe in terra era pratica diffusa in passato considerare la sola componente orizzontale del moto sismico trascurando quella verticale. Quest’ultima, invece, potrebbe avere un ruolo importante sulla risposta sismica delle dighe, specialmente in condizioni near fault, data la contestualità di forze d’inerzia significative agenti in entrambe le direzioni.
L’articolo descrive uno studio numerico svolto attraverso approcci semplificati e avanzati, con l’obiettivo di indagare l’effetto della componente verticale del moto sismico sulla risposta di una diga in terra zonata. L’opera, situata nel sud Italia, ha la peculiarità di essere stata colpita, durante la sua fase di costruzione, dall’evento sismico dell’Irpinia del 1980 con epicentro a pochi chilometri dallo sbarramento. Le analisi numeriche sono state condotte applicando in input (i) entrambe le componenti del moto (orizzontale e verticale), (ii) la componente verticale con segno invertito e, infine, (iii) ignorando completamente la componente verticale. I risultati ottenuti mostrano che il contributo della componente verticale del moto di input sugli spostamenti permanenti del corpo diga è quasi sempre trascurabile per le analisi di tipo avanzato, in grado di portare in conto la non linearità e la plasticizzazione diffusa del corpo diga, mentre ha un ruolo maggiore sulle previsioni numeriche ottenute tramite l’approccio dinamico semplificato alla Newmark (1965)
VALUTAZIONE DEGLI EFFETTI DI SITO NELLA CITTÀ DI SALERNO: CONFRONTI CON LE INDICAZIONI DELLA NORMATIVA SISMICA NAZIONALE ED EUROPEA
No full textEvaluation of the natural vibration frequencies of a historical masonry building accounting for SSI
No full textThe dynamic identification of a historical masonry palace located in Benevento (Italy) has been carried out. The case study is representative of many buildings located in historic Italian centres. Since the building has been instrumented by the Department of Civil Protection with a permanent dynamic monitoring system, some of the recorded data, acquired in various operating conditions have been analysed with basic instruments of the Operational Modal Analysis in order to identify the main eingenfrequencies and vibration modes of the structure. The experimental results have been compared to the numerical outcomes provided by a detailed three-dimensional Finite Element (FE) model of the building where Soil–Structure Interaction (SSI) has been taken into account. The comparison of experimental vs. numerical frequencies and vibration modes of the palace evidenced the role exerted by the subsoil on the dynamic response of the building
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