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 consistent, uniform pressing of green bodies is a necessary part of producing high-quality, high-performance ceramics with predictable qualities and behavior. Undesirable density variation in the compacted ceramic powder causes variability in performance, failure to meet quality control standards, and, possibly, complete piece failure during successive processing. These issues contribute directly to a decrease in production efficiency through lost time and an increase in energy and material use. The careful control of the green body density field is of the utmost importance to consistently producing high-performance ceramics. Current methods for minimizing heterogeneity of the density field are often based on trial-and-error to optimize mold geometry and forming pressure, which is both expensive and prolongs development. The present research presents a continuum-level constitutive model for accurately modeling the densification of ceramic powders into green bodies and outlines the numerical implimentation of said model. The constitutive model incorporates nonlinear elasticity, elatic-plastic coupling, cap evolution, pressure- and Lode angle-dependent plasticity, and hardening. To evaluate the constitutive model, a new method for measuring density in green bodies has been developed. This method utilizes readily-available laboratory equipment to produce density projection data for the sample and subsequently processes that data to produce a 3D density field using well-developed tomographic reconstruction techniques. Finally, a green body is produced from alumina powder (Martoxid KMS-96) and the density field is evaluated and compared to that of a numerical simulation. They are shown to agree within the error of the density measurements. These comparisons demonstrate the performance of the developed constitutive model and the potential utility for companies and research institutions that are in the ceramics production field.

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.

After-earthquake assessment of buildings in terms of usability and safety is nowadays performed by in-charge technicians which are called to give their judgment basing mainly on in-field surveys and visual inspections. This necessarily implies additional inconvenience for residents and economic losses in the affected area, being often large the time required for conducting the surveys and being the judgment on the safe side in absence of objective data. A near real-time assessment based on objective data related to the seismic response of the structures is possible though the use of a monitoring systems capable of providing information on the state of the monitored structure inferring observations of its dynamic response. One of the most reliable parameter which can be correlated to the state of condition of a structure after an earthquake is the ductility demand expressed in terms of interstory drift. The use in monitoring systems of this indicator is examined in this thesis through case studies on reinforced concrete framed buildings and precast industrial buildings. In the design process of the systems I proposed a capacity-demand approach, through the prior formal definition of the requirements of accuracy and the calculation of the actual accuracy of the designed monitoring system. In particular I investigated in detail the uncertainties, both instrumental and related to model, to be combined in order to obtain the overall uncertainty of the information provided by the monitoring system, when using the method of double integration of the acceleration measurements. I have found that in general the instrumental uncertainties have less importance to the uncertainties of the model, in particular in presence of residual displacements at the end of the seismic motion. Aiming to reduce uncertainties in the presence of residual displacements and to cancel the need of high-pass filtering acceleration signals, I proposed a sensing bar prototype instrumented with accelerometers and inclinometers.

Hybrid Simulation with Dynamic Substructuring (HSDS) is a mixed numerical/- experimental simulation techniques. In detail, HSDS combines a Physical Substructure(PS) -the most critical subpart- with a Numerical Substructure (NS), and a compliant time integration process calculates the overall dynamic response of the emulated system. With the objective to circumvent three among major limitations of HSDS, the present thesis offers methodological procedures and algorithms aimed at: i) emulating a consistent degradation between PSs and NSs via model updating techniques; ii) handling PSs characterized by several internal DoFs with a reduced number of interface actuation points; iii) improving the computational efficiency in the case of complex NSs via partitioned time integrators. An old reinforced concrete bridge and a steel piping network for industrial plants are introduced as full-scale structural case studies. Part of significant results were published on referee journals and proceedings of international conferences. Part of developed tools was uploaded to the NEESHub web repository that is a United States web platform for research, collaboration and education powered by the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES).

Through a second-order homogenization procedure, the explicit relation is obtained between the non-local parameters of a second gradient elastic ma- terial and the microstructure of a composite material. This result is instru- mental for the definition of higher-order models, to be used for the analysis of mechanics at micro- and nano-scale, where size-effects become important. The obtained relation is valid for both plane and three-dimensional prob- lems and generalizes earlier findings by Bigoni and Drugan (Analytical deriva- tion of Cosserat moduli via homogenization of heterogeneous elastic materials. J. Appl. Mech., 2007, 74, 741753) from several points of view: i) the result holds for anisotropic phases with spherical or circular ellipsoid of inertia; ii) the displacement boundary conditions considered in the homogenization procedure is independent of the characteristics of the material; iii) a perfect energy match is found between heterogeneous and equivalent materials (instead of an optimal bound). From the obtained solution it follows that the equivalent second-gradient Mindlin elastic solid: a) is positive definite only when the discrepancy tensor is negative defined; b) the non-local material symmetries are the same of the discrepancy tensor; c) the non-local effective behaviour is affected by the shape of the RVE, which does not influence the first-order homogenized response. Finally, explicit derivations of non-local parameters from heterogeneous Cauchy elastic composites are obtained in particular cases.

The hyporheic zone is often defined as the zone where mixing of surface water and groundwater occurs in shallow sediments beneath and adjacent to rivers. This mixing contributes to create unique biogeochemical conditions that may attenuate contaminants from either upstream surface water or groundwater under gaining and losing conditions. Hyporheic exchange results from differences in the channel near-bed head as it varies in space in response to interactions between surface flow and bed topography, with the interaction with the water table playing an important role too. Reactions of contaminants in groundwater also dependent on mixing between surface and subsurface water, which occurs in this zone. Therefore, representation of the profile of upwelling and downwelling exchange between surface water and groundwater have important consequences for contaminant transport. The present work studies nitrogen fate within a restored reach of the River Bure, Norfolk, United Kingdom. To this end, we confront numerical simulations of the hyporheic flow and tracer transport with field measurements of surface flow properties, nearby groundwater table and nitrogen compound concentration. We numerically model mixing between hyporheic flow paths induced by sediment, bedform, meanders on riverbed, and flow paths of adjacent upwelling of deeper groundwater. Results of the analysis indicate that despite the coarse topographical data and with limited surface water hydraulic data it is possible to define the spatial extent of hyporheic exchange and potential mixing zones for contaminants as a function of residence time. The proposed work has the potential to depict high residence time zones and biogeochemical reactivity in homogeneous and heterogeneous sediments. Furthermore, fieldwork analysis shows that in this site the hyporheic zone have a little effect on nutrient concentration. In addition, hydraulic modeling results indicate that streambed discharge significantly influences hyporheic exchange. Especially, the residence times under average stream discharge conditions are higher than the ones under the high discharge conditions mostly on the part that has riffle - pool morphology. From hydraulic point of view, heterogeneous domain has higher connectivity than the homogeneous fine sand subsurface set. Such that, subsurface flow has tendency to flow through high hydraulic conductivity zones, which is defined as tunneling effect, therefore, low conductivity zones have minor effect on hyporheic flow. The predictions based on the DaO2 index proves that heterogeneous sediment formations have more aerobic potential, however, prevailing anaerobic conditions occur mostly vicinity of low hydraulic conductivity zones.

An approach based on genetic algorithm and parallel computing has been presented and discussed for structural optimizations. Some details on its software implementation are given and explained. Numerical simulations demonstrate the applicability of the proposed approach for the optimization of large-scale real structures.