This doctoral thesis deals with evaluation of the mechanical performance of brick-mortar masonry after high temperature exposition, by means of a theoretical and experimental research as well as finite elements analyses. The general aims are to assess the residual mechanical properties of masonry and its components and to define a constitutive law accounting for high temperature damage. To these purposes, high temperature exposition was reproduced by means of a brick furnace; then, mechanical testing was performed on the damaged and undamaged material samples; finally, the experimental results were employed to define theoretical-experimental constitutive laws as well as to set up finite elements analyses. The reliability and applicability of the proposed model is finally discussed, with reference both to the state-of-the-art and to possible further research. / La presente tesi affronta il problema della valutazione delle prestazioni meccaniche della muratura di malta e mattoni successivamente all’esposizione ad alte temperature, attraverso uno studio sperimentale e teorico ed analisi meccaniche agli elementi finiti. Gli obiettivi posti si sostanziano nella valutazione delle proprietà meccaniche residue del materiale muratura e dei suoi componenti e nella definizione di una legge di deterioramento meccanico per la muratura danneggiata dall’esposizione alle alte temperature. Al fine di tali obiettivi, per mezzo di un forno di cottura per laterizi è stata prodotta la simulazione fisica dell’esposizione ad alte temperature; quindi, prove di caratterizzazione meccanica sono state compiute sui materiali esposti e non esposti, ed infine i dati sperimentali sono stati utilizzati sia per la costruzione di modelli teorico-sperimentali di comportamento dei materiali sia per il confronto dei modelli stessi con le risultanze di analisi agli elementi finiti che rappresentano le condizioni della muratura integra e danneggiata. Infine, è discussa la validità ed applicabilità del modello proposto in relazione sia allo stato dell’arte sia ad eventuali sviluppi futuri.

Over the last two decades, the production of excess sludge has increased rapidly due to a more stringent legislation on effluent quality and a growing number of new plants, becoming an economic and an environmental critical issue. Processing excess sludge could account for half up to 65% of the total operation costs of a wastewater treatment plant. Technologies to reduce the excess sludge had been widely studied. Several studies reported that the technologies integrated in the wastewater handling units should be cost effective and preferable rather than the techniques integrated in the sludge handling units, as they allow to reduce the sludge production rather than treat it. Thus, the development and the optimization of a technology able to reduce the sludge production in the water line is now challenging. A lot of technique have been developed such as biological, thermal, high temperature oxidation, mechanical treatments, ultrasonication, ozonation or by using chemical compounds. Some of these have been proven not energy saving, while others can negatively affect the effluent quality of the process due to the formation of by-products. Among others, biological treatments are a challenging strategy for sludge reduction. In recent years, several studies showed that including an anaerobic bioreactor in the returned activated sludge line of a conventional activated process could significantly enhance the sludge reduction without causing negative effects on operational performances. Today, this configuration is known as anaerobic side-stream reactor (ASSR) process. Several laboratory applications highlighted that the sludge yield of the ASSR process could be reduced up to 60% compared to a conventional activated process. Despite the highest percentage of sludge reduction achieved, the process is still little applied to real scale because its main operating parameters and sludge reduction mechanisms are still unclear. This study focused on the verification of ASSR process, the mechanisms of sludge reduction and the microbial structure of the process. During the first part of the research, a laboratory experimental system was designed and implemented. A sequencing batch reactor (SBR), to simulate the water line of a real wastewater treatment plant, and an ASSR as a sludge treatment unit composed the system. Unlike most of the previous studies, the system was fed with real urban wastewater in order to obtain results that reflect as much as possible what can really happen to a municipal WWTP. Through a critical analysis of the literature, the influence of two important operating parameters, such as the solid retention time (SRT) of the ASSR and the interchange rate (IR), which means the percentage of biomass cycled into the ASSR, had been uncovered Given this, the experimental system was started up and reached a stable condition after 60 days. The research was developed in three different phases that lasted for about 90 days each. The experimental lab system was tested under three configurations: i) 10% sludge interchange rate and SRT in the ASSR of 10 days; ii) 20% sludge interchange rate and SRT in the ASSR of 5 days and iii) 40% sludge interchange rate and SRT in the ASSR of 2.5 days. The observed sludge yield (Yobs) of each phase was evaluated and was equal 0.21 g TSS/g COD, 0.14 g TSS/g COD and 0.12 g TSS/g COD in Phase I, II and III, respectively. These results confirmed that the process could significantly decrease the sludge production and a reduction up to 62% could be achieved. To explain the results obtained in terms of sludge reduction, different tests and analysis were performed. The release of soluble COD and ammonia in the ASSR have highlighted that the endogenous decay and cell lysis mechanism occur in the ASSR. Extraction of EPS, with CER and BASE methods, showed a release of protein and polysaccharides in the bulk solution that increased passing between Phase I and III. At the end of each experimental phase, batch tests were carried out to evaluate the activity of phosphorus accumulating organisms (PAO) and denitrifying phosphorus accumulating organisms (DPAO). Recirculation in SBR-ASSR selects DPAO microorganisms. This was a result of great interest because DPAO could enhance the biological nutrient removal since nitrogen and phosphorus can be simultaneously removed. Furthermore, DPAO has lower cell yield than PAO resulting in lower sludge production. Results showed an activity of PAO, DPAO and other slow growers such as sulfate reducing bacteria. All these results suggested that the high percentage of sludge reduction could be explained as a combination of aspects, such as the cell lysis, the cryptic growth, the selection of slowing microorganisms and EPS destructuration. The SRT and the IR could be considered as main parameters and their variation could significantly affect the performance of the process. Microbial analyses were carried out to investigate the bacterial and archaeal structure of the ASSR sludge during each phase.The results confirmed the presence of several bacteria that are typically heterotrophic responsible of hydrolysis and fermentative process of organic matter. Several slow growers bacteria were also detected. Moreover, according to the batch tests on PAO and DPAO activity, a relevant increase in Phase III of some genera able to enhance the biological phosphorous removal has been observed. In summary, the research found that the ASSR process is a sustainable solution for the sewage sludge reduction due to an efficient and a low sludge production, able to ensure both carbon, nutrients and phosphorous removal applying an extremely simple technology, easy to realize both in new and in existing wastewater treatment plants.

This work analyses the behaviour of in-plane timber floors which are differently refurbished. The task is to ascertain the stiffness of the different solutions and to study the influence on the global behaviour of the building. The first type analysed is a floor with simple boards to which different reinforcing techniques have been applied. These are double boards, steel plates, diagonally set FRP strips, glued plywood panels and concrete slabs. For each of these types of reinforcement experimental displacement control tests were carried out. They were monotonic and cyclic tests of specimens with dimensions 2x1 m and 5x4 m, with and without perimeter tie-beams. The same tests were numerically reproduced and a numeric model of simple implementation was created able to simulate non-linear behaviour of floor and tie-beam. On the end, the floor model was used in order to analyse a traditional building. Experimental analysis and numeric modelling confirmed the need to guarantee efficient floor-masonry connections and showed the notable contribution offered by perimeter tie-beam in terms of in-plane floor stiffness. The comparison between different techniques of reinforcement showed the inadequacy of simple boards to stand up to seismic action.

Whenever two bodies are in contact due to a normal load and one is sliding against the other, a tangential force arises, as opposed to the motion. This force is called friction force and involves different mechanisms, such as asperity interactions, energy dissipation, chemical and physical alterations of the surface topography and wear. The friction coefficient is defined as the ratio between the friction force and the applied normal load. Despite this apparently simple definition, friction appears to be a very complex phenomenon, which also involves several aspects at both the micro- and nano-scale, including adhesion and phase transformation. Moreover, it plays a key role in a variety of systems, and must be either enhanced (e.g. for locomotion) or minimized (e.g. in bearings), depending on the application. Considering friction as a multiscale problem, an analytical model has been proposed, starting from the literature, to describe friction in the presence of anisotropy, adhesion and wear between surfaces with hierarchical structures, e.g. self-similar. This model has been implemented in a MATLAB code for the design of the tribological properties of hierarchical surfaces and has been applied to study the ice friction, comparing analytical predictions with experimental tests. Furthermore, particular isotropic or anisotropic surface morphologies (e.g., microholes of different shapes and sizes) has been investigated for their influence to the static and dynamic friction coefficients with respect to a flat counterpart. In particular, it has been proved that the presence of grooves on surfaces could decrease the friction coefficients and thus reduce wear and energy dissipation. Experimental tests were performed with a setup realized ad hoc and the results were compared with full numerical simulations. If patterned surfaces showed that they can reduce sliding friction, other applications could require an increase in energy dissipation, e.g. to enhance the toughness of microfibers. Specifically, the applied method consists of introducing sliding frictional elements (sliding knots) in biological (silkworm silk, natural or degummed) and synthetic fibres, reproducing the concept of molecules, where the sacrificial bonds provide higher toughness to the molecular backbone, with a hidden length, which occurs after their breakage. A variety of slip knot topologies with different unfastening mechanisms have been investigated, including even complex knots usually adopted in the textile industry. The knots were made by manipulation of fibres with tweezers and the resulting knotted fibres were characterized through nanotensile tests to obtain their stress-strain curve until failure. The presence of sliding knots strongly increases the dissipated energy per unit mass, without compromising the structural integrity of the fibre itself.

This thesis focuses on fatigue problem on riveted structures and the correlated experimental tests. The term “fatigue” denotes the cracking of metals under repeated loading. The technique of riveting structures is obsolete due to the low level of standardization in the construction process. Knowledge concerning riveted structure’s ability to withstand fatigue has not been investigated to the same extent as for modern structures assembled by welding. Nevertheless, many riveted structures are still in service after over 100 years. Clamping force originates when the hot rivet is placed into the hole of the plates and the rivet shorten in length due to cooling. In Europe, a large number of railway bridges are riveted. Moreover, all over the world, the rivet assembly technique has been largely used for different types of buildings. The riveted structures are subjected, evidently, to fatigue degradation as all the other steel structures. The riveted joint complexity and the non-uniform realization lead to a structure-specific consideration. In Europe, current regulations recognise only one fatigue class for riveted structures neglecting the clamping force effect. This approach is characterized by an elevated standard deviation for the assessed results. This research aims to improve the riveted structures fatigue comprehension and to propose appropriate tests. Some elements have been extracted from a dismantled railway bridge located near San Stino di Livenza (Venice). An innovative clamping test (TCT) has been conceived: applying a torsional moment to the rivets and evaluating the sliding friction, the clamping force has been estimated. Contrary to traditional clamping tests, this setup, at an affordable price, provides good precision. Moreover, the test is in-site and does not provoke damages to the examined structure. Fem models of rail bearer have been realized taking into account rivets, holes and multilayer plates section inertia. A specific laboratory set up has been designed with the intention to calibrate the fem models. Frictions and clamping force have been taken into account in the rail bearer models. There is a close correspondence between the non-linear models and the experimental tests. The clamping assumptions, derived from the TCT, have been verified. A full scale fatigue test has been prepared and the first cycles have been monitored. Full scale fatigue tests are sophisticated and involve many parameters. For this test, a specific metallic frame has been designed and realized using advanced fatigue models. An advanced analysis (hot spot method) has been carried out, for the frame, in order to evaluate the stress into the welds. This frame will be used by the DICEA laboratory to test, principally, specimens extracted from bridges.

The interaction between frames and infills in case of earthquake is a topic of great significance in structural engineering. Infills, often considered non-structural elements, in fact behave as they were. Sometimes they make low engineering buildings behave better than one would expect, other times they are responsible of rather bad seismic performances even in recently built constructions. Infills, often stiff and brittle if constructed with common fired bricks and strong mortar, are able to change to a great extent the seismic structural response, invalidating many of the basic design assumptions. Nevertheless, it is not possible to think of buildings without infills, due to the requirement of controlling energy consumption for residential climate control. To overcome this problem, the possibility of assembly ductile infills was investigated in the current thesis. The basic idea was to use weakness as the main tool, pursued both through the choice of materials and the proposal of a new, simple though effective building technique. Particular attention was devoted to adobe (earthen bricks) infills, specifically chosen in a structural perspective to take advantage of the intrinsic weakness, often unacceptable for other applications. Sustainability and thermo-hygrometric performances are considered important characteristics, even though background themes in comparison with weakness, according to the main perspective of this research work. The aim of the research was to evaluate the possibility of forcing a predefined damage pattern, consistent with reuse requirements, by means of ductile mechanisms. The modus operandi was to lay weak (horizontal) surfaces in the panels, breaking their continuity to allow a frictional, stable and ductile sliding to take place. The idea was investigated both numerically and experimentally. During a first phase, shear behavior of mud mortar joints was tested. Then, four full scale panels, confined by a steel frame, were subjected to lateral cyclic load. The four tests differed both in building technique, traditional or with internal partitions, and in material, hollow clay bricks or adobes. The experimental work was then extended numerically by means of FE analysis (through two modeling techniques) to different geometrical and mechanical situations. Attention was focused on the role of partitions in the structural response and on the possibility of capturing global behavior through a local calibration (on small assemblies) of model parameters. As a conclusion, the use of partitioned adobe infills was proposed in association with ductile timber frames because of the compatibility of materials. The solution may provide adequate stiffness and energy dissipation in case of earthquake. Moreover, this kind of buildings usually suffer for a lack of summer thermal insulation: the addition of mud infilling would improve such a performance.

Lo scopo di questo lavoro è stato di sviluppare un programma ad elementi finiti tridimensionale, scritto in Fortran 90, in grado di rappresentare il comportamento di interfaccia di travi in calcestruzzo rinforzate da fogli di FRP, sia in fase elastica, che durante il fenomeno di delaminazione utilizzando la teoria del danno. Si è inoltre indagato sul comportamento del collegamento FRP-cls a causa di carichi a lunga durata, mediante una sperimentazione e attraverso simulazioni numeriche. Il modello FEM si basa sulla teoria del contatto [1] legata al danneggiamento per poter simulare tutto il processo di delaminazione partendo dall’innesco dovuto al superamento del limite di resistenza del collegamento, fino al distacco completo del rinforzo. La modellazione tridimensionale ha consentito ancora, di poter ottenere lo stato tensionale su tutta l’interfaccia, riuscendo quindi a rappresentare il comportamento “di bordo” bidimensionale delle tensioni di taglio riscontrato da numerosi autori in fase di sperimentazione[2],[3], nonché gli effetti di peeling. I test a lungo termine atti a caratterizzare i parametri viscosi dei materiali, sono stati effettuati attraverso prove a trazioni dei materiali costituenti le matrici polimeriche dell’FRP (resine epossidiche), e attraverso prove su travetti rinforzati da fogli di fibre in carbonio monodirezionali, soggetti a carichi concentrati. Numericamente i fenomeni differiti sono stati studiati implementando materiali di tipo elastoviscosi sia per il calcestruzzo, utilizzando il modello B3 proposto da Z. Bazant [4], che per l’FRP impiegando un modello micromeccanico proposto in [5]. BIBLIOGRAFIA [1] P. Wrigger, (2002), “Computational Contact Mechanics”, Springer. [2] C. Pellegrino, D. Tinazzi, C. Modena, (2008), “Experimental study on Bond Behavior between Concrete and FRP reinforcement”, J. Compos. for Constr.,vol 12(2), 180-189. [3] K. V. Subramaiam, C. Carloni, L. Nobile, (2007), “Width effect in the interface fracture during shear debonding of FRP sheets from concrete”, Eng. Frac. Mech., vol. 74, 578-594. [4] Z. Bazant and S. Baweja, Creep and shrinkage prediction model for analysis and design of concrete structures: Model B3, in Adam Neville Symposium: Creep and Shrinkage – Structural Design Effects, ACI SP-194, A. Al-Manaseer Ed., Am. Concrete Institute, Farmington Hills, Michigan, 1–83, 2000. [5] L. Ascione, V.P. Berardi, G. Mancusi, (2003), “Il Comportamento a lungo termine sotto carichi statici di travi in c.a. placcate con lamine di FRP”, XXXII Congresso AIAS, Salerno. [6] S. T. Smith, J. G. Teng, (2001), “Interfacial stress in plated beams”, Eng. Struc., vol. 23, 857-871.

Air pollution is still the cause of several diseases, among which cancer is often associated to excessive or anomalous exposure to air pollutants. In addition to well-known sources of emission of air pollutants, several activities are still unregulated or not adequately controlled by conventional removal technologies; furthermore, the presence of local criticalities may elude the conventional monitoring approach. This thesis aims at providing new options to detect anomalous situations of exposure and to minimize the impacts of air pollutants by acting on two different levels: the prevention of excessive intakes and the prevention of emissions into the atmosphere. Carcinogenic organic air pollutants will receive special attention in this thesis. After a short introduction to the topic, in the second chapter of this thesis, potential critical situations of exposure are presented, with a special focus on two of the most potent carcinogenic air pollutants: dioxin and benzene. Open issues regarding both the lack of regulations for some activities and the inadequacy of some conventional monitoring approaches are described. Proposals for integrative monitoring techniques and methodologies for exposure assessment are then briefly presented. Four of them were developed during this doctoral research and are described in more details in the third chapter of this thesis; the purpose of these methodologies is to offer additional tools to detect anomalous situations of exposure to air pollutants, in both rural and urban contexts, and to estimate the dominant source of exposure to specific compounds in an area. The fourth chapter is dedicated to presenting a proposal for a limit value of dioxin deposition to soil. Dioxin are able to accumulate in the food chain; therefore, this chapter presents the development of a reverse food-chain model, starting from the Tolerable Daily Intake proposed by the World Health Organization, running through the food chain backwards on the basis of the diet of a population and determining a safe value to preserve fields and pastures. Such method represents an attempt to overcome the current absence of a regulatory limit value for atmospheric deposition of dioxin to soil. This approach aims at reducing the potential exposure to dioxin by preventing excessive intake. In the fifth chapter, a critical analysis on biofilters is carried out. Biofilters are a specific kind of air pollution control technology, widely used to treat air streams with low concentrations of volatile organic compounds (VOCs). Biofilters may be inefficient under unsteady conditions of inlet loading rate; in addition, when treating high flow rates, biofilters cannot guarantee a proper dilution of the plume in the atmosphere, due to intrinsic design reasons. Biotrickling filters (BTFs) are here presented in a review as a more efficient alternative; the improvements in air quality obtained when replacing a biofilter with BTFs are also highlighted through dispersion simulations. This chapter aims at proposing an alternative to reduce exposure directly at the emission level, rather than at the receptor level. The same aim is pursued in the final part of this thesis, in which an innovative VOC removal technology is studied: non-thermal plasma (NTP). Two laboratory activities are presented: initially, NTP is applied to treat two mixtures of air and VOCs, chosen to represent typical emissions from real industrial activities; the positive results in terms of VOC removal and the partial formation of more soluble byproducts led to a second exper-imental activity in which NTP was applied as a pre-treatment to a biofilter. NTP revealed to be a promising option to manage peaks of inlet loading rate, which biofilters are often subject to in real cases.

Localized deformation patterns are experimentally observed to prelude failure in many ductile materials (such as metal, alloy, granular material and plastic) and in quasi–brittle materials (such as concrete and rock). Moreover, the presence of a second phase in composites may promote failure due to stress concentrations at the inclusion boundaries. In order to investigate shear bands nucleation, propagation and interaction with a second phase or a defect, analytical solutions for an infinite nonlinear elastic solid subject to a uniform far–field deformation increment are obtained for the following types of inclusion: i) A crack, revealing features related to the interaction between shear bands and crack tip fields. This solution is also fundamental to the understanding of the shear band problem; ii) A rigid line inclusion, the so-called ‘stiffener’, showing the emergence of shear bands at the stiffener tips in highly deformed ductile materials. For null prestress the solution is shown to match correctly with photoelastic experiments and to predict the fracture patterns for a brittle material containing a stiffener; iii) A pre–existing shear band, showing that the deformation is highly focussed and aligned coaxial to the shear band and the energy release rate to blow up to infinity, for incremental loading occurring when the prestress approaches the elliptic boundary, so that the propagation becomes ‘unrestrainable’. All these analytical results substantiate the experimental observations that shear bands emerge at the inclusion tips and they are preferential near-failure deformation modes.

When hybrid simulation (HS) with substructures is employed for assessing the seismic behavior of a large complex structure, it is unrealistic to test all the components that may exhibit strong nonlinearity. Hence, the accuracy of the numerical substructure (NS) faces an increased challenge. To this end, this paper will emphasize on improving the accuracy of the NS in hybrid simulation based on the model updating approach. Most hybrid simulations with model updating (UHS) focus on updating the parameters of the component constitutive model (story shear model) leading to large modeling errors and the unknown detail responses. Moreover, the most extensively used component constitutive models, such as the Bouc-Wen model, are the models in a narrow sense because they are different for various RC members when the size of the component, boundary conditions, axial compression ratio, and the volumetric stirrup ratio are different from one component to the other. Thus, numerous parameters are needed to describe the displacement-force relations of different components, which leads to the huge computational burden. With this respect, this paper proposes a novel hybrid simulation approach based on identifying and updating the parameters of the material constitutive model. The main work and results are concluded as follows, 1. The unified constitutive model of unconfined and confined concrete is derived from the existing uniaxial concrete constitutive models by introducing the volumetric stirrup ratio. 2. To solve the problem that the relation of the measurements (force of the specimen of a RC member) and the identified parameters (concrete constitutive parameters) are difficult to analytical expressed, an OpenSees embedded unscented Kalman filter is proposed for parameter identification. To this end, several parts of the OpenSees source codes are developed and modified. 3. The proposed identification method and hybrid simulation based on updating the concrete constitutive parameters are respectively validated through a monotonic loading test on a RC column and a UHS on a RC frame. The results show that the convergence values of each parameter under various experimental cases are close to each other with a small variance, which indicates that the proposed identification method is robust and reliable. Comparing to the standard HS, the accuracy of the NS, hence the UHS, is significantly improved. 4. Apply the proposed UHS to a RC continuous rigid bridge with tall thin-walled piers. It concludes that the performance of the identification method is still quite good. Contrasting to the simpler structure, the improved accuracy of a large complex structure is even greater. Moreover, the accuracy of the NS can be greatly increased even though the model error is increased. By tuning the initial values of constitutive parameters, the negative influence of model error is decreased to further improve the precision of the NS. By observing the specimen, it is found that the thin-walled hollow section specimen is a bending-shear type damage mode and finally damaged due to the tensile rupture of the stirrup.