Con la presente tesi si è inteso studiare le possibilità applicative di una particolare tipologia strutturale dotata di isolamento sismico “di piano”, intendendosi con ciò una struttura in cui l'intero piano terra, tramite l'inserimento di opportuni elementi dissipativi isteretici ed in analogia al consueto isolamento sismico di base, agisce da “strato” di protezione passiva per i piani sovrastanti. A riguardo, fra le possibili soluzioni per realizzare effettivamente tale isolamento "di piano" è stata considerata la disposizione di particolari elementi dissipativi isteretici di controvento detti Crecent-Shaped Braces, caratterizzati da una forma bilatera o curva, tale comunque da presentare un'eccentricità non nulla fra l'asse del controvento stesso e la linea congiungente gli estremi. / In this PhD thesis a particular type of structure with "first-story" seismic isolation is studied, i.e. a structure in which the entire first floor, through the insertion of appropriate hysteretic dissipative elements and in analogy to the usual seismic base isolation, acts as a "layer" of passive protection for the floors above. Among the possible solutions to achieve this "first-story" isolation a particular hysteretic dissipative bracing element, the Crescent-Shaped Brace, is considered; it is characterized by a shape presenting some eccentricity between the axis of the brace itself and the line joining its ends.

The aim of this study was to investigate the influence of the diaphragm flexibility on the behavior of out-of-plane walls in masonry buildings. Simplified models have been developed to perform kinematic and dynamic analyses in order to compare the response of walls with different restraint conditions. Kinematic non linear analyses of assemblages of rigid blocks have been performed to obtain the acceleration-displacement curves for walls with different restraint conditions at the top. A simplified 2DOF model has been developed to analyse the dynamic response of the wall with an elastic spring at the top, following the Housner rigid behaviour hypothesis. The dissipation of energy is concentrated at every impact at the base of the wall and is modelled through the introduction of the coefficient of restitution. The sets of equations of the possible configurations of the wall, depending on the different positions of the centre of rotation at the base and at the intermediate hinge have been obtained. An algorithm for the numerical integration of the sets of the equations of motion in the time domain has been developed. Dynamic analyses of a set of walls with Gaussian impulses and recorded accelerograms inputs have been performed in order to compare the response of the simply supported wall with the one of the wall with elastic spring at the top. The influence of diaphragm stiffness Kd has been investigated determining the variation of maximum displacement demand with the value of Kd. A more regular trend has been obtained for the Gaussian input than for the recorded accelerograms.

Nella presente tesi è proposta una metodologia per lo studio e la valutazione del comportamento sismico di edifici a telaio. Il metodo prevede la realizzazione di analisi non-lineari su modelli equivalenti MDOF tipo stick, in accordo alla classificazione data nel report FEMA 440. Gli step per l’applicazione del metodo sono descritti nella tesi. Per la validazione della metodologia si sono utilizzati confronti con analisi time-history condotte su modelli tridimensionali dettagliati delle strutture studiate (detailed model). I parametri ingegneristici considerati nel confronto, nell’ottica di utilizzare il metodo proposto in un approccio del tipo Displacement-Based Design sono lo spostamento globale in sommità, gli spostamenti di interpiano, le forze di piano e la forza totale alla base. I risultati delle analisi condotte sui modelli stick equivalenti, mostrano una buona corrispondenza, ottima in certi casi, con quelli delle analisi condotte sui modelli tridimensionali dettagliati. Le time-history realizzate sugli stick model permettono però, un consistente risparmio in termini di onere computazionale e di tempo per il post-processing dei risultati ottenuti. / A new methodology for the study and evaluation of the seismic response of buildings is presented. The method involves the use of non-linear time-history analysis on equivalent MDOF stick models, according to the classification given in Report FEMA 440. The steps for implementing the method are described in the thesis. For the validation of the methods the results obtained were compared to that obtained by time-history analysis on detailed three-dimensional models of the structures studied (detailed model). The engineering parameters considered in the comparison, in order to use the proposed method in a Displacement-Based Design approach, are the top displacements, the inter-storey drifts, the forces at the floor and the base shear. The results of the conducted analyzes, on the equivalent stick models, match satisfactorily, in an excellent way in certain cases, those of the analyzes carried out on detailed model. The time-history on the stick model, however, allow a considerable saving in terms of computational effort and time for the post-processing of results.

Il presente lavoro ha lo scopo di presentare gli studi e i risultati ottenuti durante l’attività di ricerca svolta sul Displacement-based Assessment (DBA) dei telai in cemento armato. Dopo alcune considerazioni iniziali sul tema della vulnerabilità sismica e sui metodi di analisi e verifica, si procede alla descrizione teorica del metodo. Sono stati analizzati tre casi studio di telai piani, progettati per soli carichi verticali e secondo normative non più in vigore che non prevedevano l’applicazione della gerarchia delle resistenze. I telai considerati, destinati ad abitazione civile, hanno diversa altezza e numero di piani, e diverso numero di campate. Si è proceduto all’applicazione del metodo, alla valutazione della vulnerabilità sismica in base alla domanda in termini di spostamento costituita da uno spettro elastico previsto dall’EC8 e alla validazione dei risultati ottenuti mediante analisi non lineari statiche e dinamiche e mediante l’applicazione dei teoremi dell’Analisi limite dei telai, proposta come procedura alternativa per la determinazione del meccanismo anelastico e della capacità in termini di taglio alla base. In ultimo si è applicata la procedura DBA per la valutazione della vulnerabilità sismica di un edificio scolastico, realizzato tra il 1969 e il 1975 in un sito caratterizzato da una accelerazione di picco orizzontale pari a 0,24g e una probabilità di superamento del 10% in 75 anni. / This work aims to present the studies and the results obtained during the research activity carried out on the Displacement-Based Assessment (DBA) of reinforced concrete frames. After some initial considerations on the issue of seismic vulnerability and methods of analysis and testing, the theoretical description of the method is presented. Three case study concerning the application of the DBA procedure to plane frames, designed for vertical loads only and according to old provisions that did not involve the application of the hierarchy of strength, are presented. The results of the procedure in terms of inelastic mechanism assumed and limit-state displaced shape are compared with results obtained by nonlinear static and dynamic analysis, performed in order to validate the displaced shape assumed, and with results of Limit Analysis, which is proposed as an alternative procedure to determine the inelastic mechanism and the base shear capacity. Finally, the DBA procedure has been applied for the assessment of the seismic vulnerability of a school building, built between 1969 and 1975 and located on a site characterized by a peak horizontal acceleration of 0.24 g and a probability of exceedance of 10% in 75 years.

L'obiettivo della tesi è stato quello di indagare il complesso problema della vulnerabilità sismica dei ponte in muratura ad arco utilizzando modelli semplificati. Dopo una descrizione dei materiali da costruzione impiegati nella realizzazione e dei principali elementi dei un ponti in muratura, si è indirizzato lo studio di un ponte ad arco situato nel comune di San Marcello Pistoiese. Viene mostrato un modello numerico che permette di descrivere il comportamento strutturale del ponte sotto azione sismica e di valutare la capacità di carico del ponte sottoposto ad una azione trasversale. In un secondo momento viene descritta la realizzazione di un modello in scala del ponte, che è stato sottoposto a prove distruttive effettuate per valutare la capacità di carico del ponte rispetto ad un ipotetica azione orizzontale. Si è cercato poi di inquadrare il problema in un modello teorico che faccia riferimento all'analisi limite. Esso descrive un cinematismo di collasso a telaio che prende spunto dal quadro fessurativo del modello in muratura. Infine sono stati presentati modelli FEM numerici in ordine di complessità crescente, cercando di inquadrare il comportamento meccanico del prototipo del ponte. Tre tipi di modelli sono rappresentati: un telaio incernierato alle estremità costituito da elementi beam con resistenza alla flessione . Il secondo tipo è costituito da una reticolare equivalente che mima lo schema del ponte ed è formato solo da bielle. Infine, il terzo tipo cerca di descrivere l'intero modello con elementi tridimensionali. / The aim of the thesis was to investigate complex problem of seismic vulnerability of masonry arch bridge by using simplified models. After a description of construction materials used in building and the principals element of a masonry bridges, the study on the arch bridge located in the municipality of San Marcello Pistoiese is reported. Numerical model, that allows to describe the structural behaviour of the bridge under seismic action and to assess the carrying capacity of the bridge subjected to a transversal action, is shown. In second moment the construction of a scale model of the bridge is described, it was subjected destructive tests made to assess the carrying capacity of the bridge compared to a hypothetical seismic action. It tries to frame the issue in a theoretical model that refers to the analysis limit. It describes a kinematics collapse of the chassis which takes its inspiration from the crack of the masonry model. FEM numerical models are presented in order of increasing complexity, seeking to frame the mechanical behaviour of the prototype of the bridge. Three types of models are shown: the first is represented by a frame consisting of linear beam elements with bending resistance hinged at the ends. The second type consists of a reticular frame equivalent in roughly the trends of the bridge and is formed only of rod-free flexural behaviour. Finally, the third type tries to describe the entire model with three-dimensional elements.

This thesis reports a study on the seismic response of two-dimensional squat elements and their effect on the behavior of building structures. Part A is devoted to the study of unreinforced masonry infills, while part B is focused on reinforced concrete sandwich walls. Part A begins with a comprehensive review of modelling techniques and code provisions for infilled frame structures. Then state-of-the practice techniques are applied for a real case to test the ability of actual modeling techniques to reproduce observed behaviors. The first developments towards a seismic-resistant masonry infill system are presented. Preliminary design recommendations for the seismic design of the seismic-resistant masonry infill are finally provided. Part B is focused on the seismic behavior of a specific reinforced concrete sandwich panel system. First, the results of in-plane psuudostatic cyclic tests are described. Refinements to the conventional modified compression field theory are introduced in order to better simulate the monotonic envelope of the cyclic response. The refinements deal with the constitutive model for the shotcrete in tension and the embedded bars. Then the hysteretic response of the panels is studied according to a continuum damage model. Damage state limits are identified. Design recommendations for the seismic design of the studied reinforced concrete sandwich walls are finally provided.

Il lavoro di tesi riguarda la caratterizzazione meccanica di un giunto, adatto per la realizzazione di differenti configurazioni in strutture intelaiate pesanti di legno, costituito da un elemento metallico flangiato collegato agli elementi strutturali in legno per mezzo di barre incollate. Questo sistema di connessione presenta alcune interessanti proprietà meccaniche in termini di prestazioni meccaniche, versatilità e prefabbricazione. Un modello analitico in grado di valutare la risposta del giunto in termini dei parametri meccanici chiave (modalità di rottura, resistenza ultima, rigidezza e capacità rotazionale) à ̈ stato proposto e validato attraverso unâ€TMampia campagna sperimentale. A tale scopo il metodo per componenti, originariamente proposto per giunti semi-rigidi in acciaio, à ̈ stato adattato per modellare i giunti acciaiolegno, consentendo l'applicazione del capacity design e permettendo di progettare connessioni in grado di presentare valori di duttilità necessari ad applicazioni in campo sismico. Le prove effettuate hanno mostrato una soddisfacente rispondenza tra i risultati teorici e quelli sperimentali: in particolare la previsione affidabile delle modalità di rottura del giunto, permette la progettazione di connessioni resistenti a momento in grado di presentare alte deformazioni plastiche senza fenomeni di rotture fragili, con un notevole grado di duttilità strutturale a livello globale e di dissipazione energetica in seguito a sisma. ENGLISH VERSION This thesis investigates the mechanical characterisation of a joint, suitable for different configurations within a heavy timber frame, consisting of a wooden element connected to a steel stub by means of an end-plate and glued-in steel rods. This connection system has some interesting properties in terms of mechanical performance, versatility and prefabrication. An analytical model to predict the joint response in terms of its key parameters (e.g. failure mode, ultimate resistance, stiffness and rotation capacity) is proposed and validated through an extensive experimental programme. The component method, originally proposed for semi-rigid joints in steel frameworks, is adapted in order to set up a feasible general model for steel–timber joints, enabling application of the capacity design approach and offering the required ductility for applications in seismic zones. The tests carried out indicate satisfactory agreement between theoretical and experimental results: the reliable prediction of joint failure modes allows design of moment-resistant connections that can sustain high plastic deformation without brittle rupture, with a remarkable degree of global ductility and energy dissipation under alternate loading.

This study deepens key issues related to the seismic emergency management and deterioration state assessment of roadway and railway infrastructural networks by proposing a series of procedures and methodologies through the use of scientific-based analyses in the field of optimal management of infrastructural assets. This thesis is subdivided in several chapters, in which, the issues of quantification of the bridge structures’ deterioration state are intertwined with those related to the estimation of the seismic vulnerability assessment, from punctual level (single bridge) to territorial scale (infrastructural network). The key topics discussed in this work are, at punctual level, statistical analyses on the effectiveness of in-situ investigations for the bridges’ seismic fragility estimation, sensitivity analyses on the influence of geometrical parameters on the seismic vulnerability assessment and the construction of fragility curves for bridges subjected to deterioration of key structural components. At territorial scale, analyses of the restoring costs for bridge stocks, construction of life-cycle curves for bridges subjected to deterioration, simulations of time-dependent earthquake scenarios for infrastructural networks and procedures for the management of seismic emergency for railway networks are presented.

Due to high seismic vulnerability and severity of possible failure consequences, petrochemical installations are often considered as “special risk” plants. Although tanks, pipes, elbows and bolted flanges have been a major concern in terms of seismic design, generally, they have not been analysed with modern performance-based procedures. This thesis will explore some important themes in seismic risk assessment with a special focus on petrochemical plants and components. In the first part of the thesis the case study of a probabilistic seismic demand analysis (PSDA) for a Refrigerated liquefied gas (RLG) subplant is presented. As a matter of fact, RLG terminals that are part of strategic facilities must be able to withstand extreme earthquakes. In detail, a liquefied natural gas (LNG, ethylene) terminal consists of a series of process facilities connected by pipelines of various sizes. In this study, the seismic performance of pipes, elbows and bolted flanges is assessed, and seismic fragility functions are presented within the performance-based earthquake engineering framework. Particular attention is paid to component resistance to leakage and loss of containment (LoC) even though several different limit states are investigated. The LNG tank, support structures and pipework, including elbows and flanges, are analysed with a detailed 3D finite element model. For this purpose, a mechanical model of bolted flange joints is developed, able to predict the leakage limit state, based on experimental data. A significant effort is also devoted to identification of a leakage limit state for piping elbows, and the level of hoop plastic strain was found to be an indicator. The second part of the thesis describes an innovative methodology to evaluate seismic performances of a realistic tank-piping system with special focus on LoC from piping elbows. This methodology relies on a set of experimental dynamic tests performed throughout hybrid simulations where the steel storage tank is numerically modelled while, conversely, the physical substructure encompasses the coupled piping network. Besides, ground motions for dynamic tests are synthetized based on a stochastic ground motion model whose input parameters are derived from the results provided by a seismic hazard analysis. Then, based on output data from the experimental tests, both a high-fidelity and a low-fidelity FE model are calibrated. Furthermore, these models are used to run additional seismic analyses using a large set of synthetic ground motions. Moreover, in order to derive the seismic response directly from inputs parameters of the stochastic ground motions model, the procedure to build a hierarchical kriging surrogate model of the tank-piping system is presented. Eventually, the surrogate model can be adopted to perform a seismic fragility analysis. Along with the line of probabilistic analysis, another contribution to this research work is a probabilistic seismic demand model (PSDM) of a steel-concrete composite structure made of a novel type of high-strength steel moment resisting frame. According to the main topic of this thesis, the procedure that is here presented can be used either in a seismic risk assessment or a fully probabilistic performance-based earthquake engineering (PBEE) framework. In detail a 3D probabilistic seismic demand analysis was performed considering the variability of the earthquake incident angle, generally not taken in account in typical fragility analyses. Therefore, the fragility curves evaluated following this approach account for the uncertainty of both the seismic action and its direction.

The mechanical behaviour of wood is highly conditioned by the duration of load with regard to both its resistance and stiffness. In particular the problem of the deformability of floors is an essential aspect in design of wooden structures since, as to ordinary span beams, the service behaviour is generally a more severe standard of verification than the ultimate limit state. This research concerned the investigation of the rheological behaviour of timber and timber-concrete composite beams through an experimental approach, in order to go deep into the different components that influence the development of the long term deflection: bending and shear creep, as well as creep of connection for composite beams. The addition of a collaborating reinforced concrete slab is an ordinary solution for improving the stiffness and resistance of wooden beams, the validity of which depends on the deformability of the connection system, in addition to the mechanical properties of timber and concrete. In this work was investigated the long term behaviour of an 8 meter span timber-concrete composite beam, with stud connection. The test was carried out indoor, in variable hygrometric conditions and the results were compared with the forecasts of the method suggested by Eurocode 5. A second area of investigation concerned the rheological behaviour of the wood subject to shear, which represents one of the less explored aspects of the research into the wood. That behaviour has been investigated through long term tests on small specimens subject to different stress levels, performed indoor at uniform temperature and variable environmental relative humidity. In that case too, the results were compared with the previsions of the codes and rheological model proposed by Toratti. By experimentally calibrating the parameters of that model was made a forecast of the creep coefficient for the service life of the structures in service class 1 and 3. The inquiry into the phenomena that cause the rheological behaviour of timber and composite beams was completed through bending tests on wooden beams and shear tests on timber-concrete and timber-lime mortar stud connections, carried out in the same ambient where the test on the composite beam was made. ------------------------------------------------------------ Il comportamento meccanico del legno è fortemente condizionato dalla durata del carico, sia in termini di resistenza, sia in termini di rigidezza. Il problema della deformabilità degli impalcati, in particolare, rappresenta un aspetto essenziale nella progettazione delle strutture in legno, poiché, per le travi di luce ordinaria, il comportamento in esercizio costituisce in genere un criterio di verifica più severo rispetto allo stato limite ultimo. Il presente lavoro di ricerca ha riguardato lo studio del comportamento reologico delle travi in legno e delle travi miste legno-calcestruzzo, mediante un approccio sperimentale teso ad approfondire le diverse componenti che contribuiscono a caratterizzare lo sviluppo della deformazione differita: la viscosità a flessione, a taglio e, nella trave mista, la viscosità della connessione. L’accoppiamento con una lastra collaborante in calcestruzzo armato rappresenta una soluzione diffusa per il miglioramento della rigidezza, oltre che della resistenza, delle travi in legno, la cui validità dipende dall’efficacia della connessione tra i due materiali, oltre che dalle caratteristiche di questi ultimi. In questa sede è stato indagato, mediante una prova di flessione di lunga durata, il comportamento deformativo di una trave mista legno-calcestruzzo di 8 metri di luce con connessione a piolo. La prova è stata condotta in ambiente interno con condizioni igrometriche variabili e i risultati sono stati posti a confronto con le previsioni del metodo suggerito dall’Eurocodice 5. Un secondo ambito di ricerca ha riguardato il comportamento reologico del legno soggetto ad azione di taglio, che rappresenta uno degli aspetti meno esplorati nelle indagini sul legno. Tale comportamento è stato caratterizzato mediante prove di lunga durata su campioni di piccole dimensioni soggetti a diversi livelli di sforzo, in ambiente controllato a temperatura costante e umidità ambientale relativa variabile; anche in questo caso i risultati ottenuti sono stati posti a confronto con le previsioni della normativa e con il modello reologico proposto da Toratti. Calibrando sperimentalmente i parametri di questo modello, è stata effettuata una previsione del coefficiente di viscosità per la vita utile delle strutture in classe di servizio 1 e 3. L’indagine sui fenomeni che determinano il comportamento reologico delle travi in legno e delle travi miste è stata completata mediante prove di flessione su travi in legno e prove di taglio su connessioni a piolo legno-calcestruzzo e legno-malta di calce naturale, condotte nello stesso ambiente in cui si è svolta la prova sulla trave mista.