Valutazione empirica dell'influenza della risposta sismica locale sul non sincronismo del moto in superficie

Le attività riassunte in questo contributo sono svolte nell’ambito del progetto di ricerca PRIN 2008: “Effetto del non sincronismo inclusa la risposta sismica locale sulla sicurezza dei ponti”, Linea 1 EQK. In tale ambito, gli Autori hanno analizzato gli effetti dell’asincronismo del moto sismico registrato da coppie di stazioni accelerometriche ubicate, a distanze dell’ordine delle centinaia di metri, su terreni con caratteristiche lito-stratigrafiche corrispondenti ad un sito di riferimento (sito R) e su sito con amplificazione stratigrafica (sito S) corrispondente nei diversi casi alle classi di sottosuolo B, C, D della Norme Tecniche per le Costruzioni (D.M. 14/1/2008). I risultati ottenuti da queste analisi preliminari mostrano che gli spostamenti differenziali valutati secondo le prescrizioni di normativa sono mediamente maggiori di quelli misurati sperimentalmente e che la formulazione analitica adottata dalla Norma è appropriata per descrivere la dipendenza di spostamenti relativi dall’accelerazione di riferimento

Evaluating the effects of a deep excavation on monumental buildings: MarmorKirken station in Copenhagen

This paper describes the Building Risk Assessment (BRA) process implemented during the design and construction of MarmorKirken metro station in Copenhagen. Being the box station very near the monumental church, the evaluation of the effects induced by the excavation on the church was a key issue of the design. Surveys, structural and geotechnical investigations were carried out to setup reliable structural and geotechnical numerical models on which BRA, at the design stage, was based. During construction works, design predictions were systematically compared with monitoring measures, allowing to update the BRA. According to BRA results, no significant effects of construction works on the church was observed.Cet article décrit le processus d'Evaluation des Risques liés aux Bâtiments (BRA) mis en œuvre lors de la conception et de la construction de la station de métro MarmorKirken à Copenhague. Le box étant très proche de l'église monumentale, l'évaluation des effets induits par les fouilles sur l'église a été un enjeu clé de la conception. Des études, des investigations structurelles et géotechniques ont été réalisées pour établir des modèles numériques structurels et géotechniques fiables sur lesquels BRA, au stade de la conception, s'est basé. Lors des travaux de construction, les prévisions de conception ont été systématiquement comparées aux mesures de suivi, permettant ainsi de mettre à jour le BRA. Selon les résultats du BRA, aucun effet significatif des travaux de construction sur l'église n'a été observé

Simplified relationships for estimating seismic slope stability

Eurocode 8 addresses seismic slope stability analysis with reference to limit state design, specifying a 50% re-duction of the peak horizontal inertia force of a potentially sliding mass. Such a coefficient has been shown to depend on several factors, including soil deformability and the frequency content of the seismic action. In this paper the reduction coefficient is expressed with reference to the above factors and compared to EC8 provisions for all soil classes. A simplified design procedure is then suggested by referring to updated correla-tions based on the Newmark sliding block model, including the influence of amplitude, duration and mean pe-riod of the ground motion on the predicted displacement. The reduction coefficient is further generalised to account for the slope ductility, i.e. the capability of sustain prescribed threshold displacements. The whole procedure has been calibrated through analyses carried out using acceleration time histories, selected from a database of records of Italian seismic events, on typical subsoil layering pertaining to the EC8 classes, also adopted by the Italian seismic Code

Coupling between 4f and itinerant electrons in SmFeAsO1-xFx (0.15 < x < 0.2) superconductors: an NMR study

$^{19}$F NMR measurements in SmFeAsO$_{1-x}$F$_x$, for $0.15\leq x\leq 0.2$, are presented. The nuclear spin-lattice relaxation rate $1/T_1$ increases upon cooling with a trend analogous to the one already observed in CeCu$_{5.2}$Au$_{0.8}$, a quasi two-dimensional heavy-fermion intermetallic compound with an antiferromagnetic ground-state. In particular, the behaviour of the relaxation rate either in SmFeAsO$_{1-x}$F$_x$ or in CeCu$_{5.2}$Au$_{0.8}$ can be described in the framework of the self-consistent renormalization theory for weakly itinerant electron systems. Remarkably, no effect of the superconducting transition on $^{19}$F $1/T_1$ is detected, a phenomenon which can hardly be explained within a single band model.Comment: 4 figure

The seismic performance of a earth dam by different displacementbased methods

The performance-based design of earth dams and the rehabilitation of existing ones require the evaluation of seismic performance based on permanent displacements caused by expected the earthquake. The paper reports a comparison between different methods with increasing complexity for estimating seismic displacements: simplified rigid block method, based on empirical relationships (Bray and Rathje, 1998; Tropeano et al., 2009); simplified uncoupled method, again based on the sliding block analysis, but accounting for soil deformability; coupled ‘stick-slip’ approach, based on a 1D lumped mass model to calculate together dynamic response of the site and movement of sliding block (Tropeano et al., 2011); 2D finite differences analyses by the FLAC code, reproducing the heterogeneity of soil and topographic effects. The methods were applied to the case of the dam of Marello mountain across the Angitola river (Southern Italy). The parameters for static and dynamic geotechnical characterization of subsoil model have been taken from the results of the site investigation published in technical reports. The spectral shape and peak ground acceleration specified by the Italian Seismic Hazard Map, representative of input motion on outcropping bedrock, allowed to choose a set of spectrum-compatible acceleration time histories to simulate the seismic input. The sliding displacements predicted using simplified method resulted strongly dependent on topographic coefficient. Both uncoupled and coupled approaches have shown conservative permanent displacements compared to Newmark method. The average displacement of the sliding block by two-dimensional finite difference analysis, considering the stiffness variability related to depth, results comparable with values obtained by other methods

2D equivalent linear analysis for the seismic vulnerability evaluation of multi-propped retaining structures

The evaluation of the seismic behaviour of underground structures represents one of the most actual seismic geotechnical and structural engineering research topics about the study of the complex phenomena of soil-structural interaction. In the last decades, different types of simplified and numerical approaches have been developed for the correct analysis of the seismic vulnerability of these important infrastructures and a series of laboratory tests for the seismic behaviour characterization of the soils (resonant column test, etc.) and of the coupled soil-structure system (centrifuge test, etc.) have been conducted, especially after the recent strong earthquakes where the underground structures have been subjected to significant damages. In the same way, in the last few years, the International Codes are beginning to pay attention to the concepts of the seismic design of these structures. Despite the significant development of knowledge, described above, still remain open several uncertainties of the correct reproduction of the underground structures behaviour under seismic load. In this paper, the evaluation of the seismic behaviour of a multi-propped retaining structure was conducted, considering the soil-structure interaction effects. The results of the 2D equivalent linear analysis are analysed in terms of bending moment acting on the concrete retaining walls.L‘évaluation du comportement sismique des structures souterraines représentent un des sujets de recherche les plus courants sismique, géotechnique et de construction, qui concerne l‘étude du phénomène complexe de l‘interaction sol-structure. Pendant les dernières décennies, différents types d‘approches simples et numeriques ont été développés pour une analyse exacte de la vulnérabilité sismique de ces infrastructures importantes et encore une série de tests de laboratoire pour la caractérisation du comportement sismique du sols (test de colonne résonnante etc.) et du système couplé du sol-structure (test de centrifugation etc.) ont été menées, après le fort tremblement de terre où les structures souterraines ont subi des dommages importants. De la même manière, pendant les dèrnieres années, les Codes Internationales ont commencé a prêter plus d‘attention aux concepts de désign sismique de ces structures. Malgré la considèrable connaissance, décrit ci-dessus, il y a quand même de l‘incertitude sur la correcte reproduction du comportement des structures sous charge sismique. Dans cet article, il a été mené l‘evaluation du comportement sismique des structures de soutenement multi-etayé, considérant que les effets de l‘interaction sol-structure. Les resultats de l‘analyse linéaire 2D equivalente sont analysées en termes de moment de flexion agissant sur les murs de soutènement en béton

Analisi numerica dell’efficacia dei muri sacrificali per la riduzione degli spostamenti indotti da scavi profondi

In questa nota si presentano i principali risultati di uno studio parametrico finalizzato al confronto dell’efficacia di diversi tipi di pareti sacrificali, cross-wall (CW) e buttress-wall (BW), nel ridurre il campo di spostamenti indotto da scavi profondi. Nelle analisi sono stati presi in considerazione diversi interassi e diverse geometrie di pareti sacrificali. Il profilo del terreno è costituito da un potente deposito di terreno argilloso sovrastato da uno strato di terreno a grana grossa, e può essere considerato tipico della zona centrale di Roma. Il comportamento del terreno è stato modellato con una legame costitutivo elastico-plastico incrudente. Sia il diaframma sia le pareti sacrificali sono state modellate con elementi solidi, così come gli elementi all’interfaccia terreno-parete e parete-parete. I risultati ottenuti dalle analisi numeriche consentono di mettere in relazione il valore di riduzione dello spostamento con i principali parametri geometrici dei muri sacrificali

Seismic displacement analysis of homogeneous slopes: a review of existing simplified methods with reference to Italian seismicity.

The simplified displacement-based procedures for seismic slope stability represent a good-working balance between simplicity and reliability, since both slope ductility (i.e. the capacity of sustain permanent displacements) and deformability (basically affecting the asynchronous slope motion) are accounted for. In this paper the procedure proposed by Bray & Rathje (1998) is reviewed with particular reference to Italian seismicity on a set of subsoil models, representative of the different soil classes specified by Italian and European codes. The relationship expressing the decrease of the equivalent acceleration with increasing earthquake/soil frequency ratio is then obtained by means of dynamic 1D site response analyses. Statistical correlations between calculated Newmark displacements, significant ground motion parameters and the ratio of seismic load resistance to peak demand are then derived and compared to similar relationships proposed in literature

Parametri di intensità sismica per la stima degli spostamenti permanenti di pendii omogenei

Gli attuali criteri di progettazione in condizioni sismiche si avvalgono di procedure legate alla valutazione della prestazione del sistema espressa in termini di perdite quantificabili (costi di riparazione), di funzionalità o di beni inestimabili (vite umane, beni storico-culturali). In tale ottica il parametro rappresentativo della risposta è correlato attraverso procedure più o meno sofisticate a uno o più parametri che descrivano le caratteristiche del moto sismico. La scelta di tali parametri deve essere effettuata attraverso criteri di efficienza e sufficienza (cfr. p.es. Tothong & Luco, 2007; Luco & Cornell, 2007) inoltre devono poter essere prevedibili attraverso opportune leggi di ricorrenza. In tale ambito, la presente nota propone una applicazione dei criteri citati per la stima della curva di pericolosità degli spostamenti cosismici dei pendii e per la valutazione critica dell’efficienza dei parametri di intensità del moto considerati significativi. In particolare vengono confrontate alcune relazioni indicate nella letteratura nazionale ed internazionale, e viene presentata una relazione che tiene conto dell’intensità di Housner, IH, quale parametro efficace per la stima degli spostamenti. Per la previsione del parametro IH viene proposta, inoltre, una legge di attenuazione in funzione di magnitudo e distanza