Design and Analysis of the Medium-β Elliptical Cavities for the European Spallation Source Accelerator

This thesis is dedicated to the design and analysis of superconductingelliptical cavities. Elliptical cavities play a central role in modern particle ac-celerators due to their high efficiency. After an introduction to the EuropeanSpallation Source project, the thesis goes through the design of the medium-βcavity. The RF design of the inner cell and end cell are presented in sequencein paper I . The design is completed by the chapter on the mechanical perfor-mances of the cavity (paper II).Papers III, IV and V are instead dedicated to the analysis of the cavity.The necessary mathematical tools for the analysis are presented in paper IIIwhich, after stating fundamental results on hollow cavities, presents a spec-tral decomposition used in the following papers. In paper IV, a time-domainmodel for the power dissipation induced by the excited higher-order-modes ispresented. Such modes are excited by the particle beam that passes throughthe cavity and are detrimental to the performances of the accelerator. PaperV presents a time-domain model of the cavity coupled to an externa circuit toa coupler. The model is functional to the design of the cavity control system

Structural Health Monitoring Issues Using Inclinometers on Prestressed Concrete Girder Bridge Decks

In the last decades, assessment and rehabilitation of the existing built environment constitute one of the major challenges for engineers, practitioners and code-makers all over the world. Aging, deterioration processes, lack of or improper maintenance, and increasing occurrence of extreme events have led to the need of more efficient methods for the safety assessment and retrofitting/rehabilitation of existing concrete structures like bridges. New approaches deriving from research should be able to provide solutions devoted to reduce and/or avoid the necessity of interventions, verifying the safety conditions for human life and performances for serviceability on aged infrastructures. Structural Health Monitoring (SHM) of existing bridges has become a key issue in all western world as most of the infrastructures of each Country are reaching the end of their design life. SHM can be divided classically in two approaches: static and dynamic. Static SHM is based on the measure of displacements and their derivatives like rotations or strains regardless of the dynamic behaviour of the structure. Clinometers are among the most used devices to measure angles on structures; they can provide high accuracy when used in static mode as advanced techniques of signal processing can be used to reduce the noise of the signal working on acquisitions that can last several seconds to provide one single accurate measure of angle. Nevertheless, many issues one the affidability and the correct use of measures done with clinometers have to be addressed to achieve a trustworthy SHM using such devices. In this paper the most relevant issues related to the f.e.m. modelling of a bridge deck in view of the use of clinometers for SHM are presented providing explanation using a test case bridge that has been under continuous investigation for many months. A brief explanation of the process for data cleaning and interpretation is also given, stressing out the limits of the technology and the possible outcomes

Cracking analysis of plane stress reinforced concrete structures

This article presents the numerical analysis' results of reinforced concrete elements subjected to plane stress in early cracking stage. The elements are modelled by a concrete two-dimensional matrix, discrete reinforcement bars and bond-slip elements. The aim of this study is to investigate the behaviour of RC structures before and after the formation of the first cracks to understand the influence on the crack spacing and width of bar orientation with respect to the crack direction, bar spacing and diameter and presence of shear stresses on the crack. Discrete crack non-linear analysis of elements with reinforcement both orthogonal and skew to the crack directions are performed. The interaction between concrete and steel is ensured by a non-linear bond slip law at the interfaces between the two materials. The crack spacing obtained numerically are compared with the ones calculated using different design codes. The analysis of models with different reinforcement geometries allows individuating and discussing the main factors governing two-dimensional plane stress concrete cracking behaviour

Autogenous Crack Control during Construction Phases of MOSE Venice Dams

The design of concrete structures exposed to severe environmental attack, like in marine environment, requires serious attention for concrete durability. Early age cracking due to autogenous deformations can be detrimental to the performance of tidal structures. The study of the structural effects of hydration heat and rheological behaviour of a set of huge concrete structures of the Mobile Venice Dams known with the MOSE acronym (Experimental Electromechanical Module) is presented in this paper. Together with other measures such as coastal reinforcement, the raising of quaysides, and the paving and improvement of the lagoon, MOSE is designed to protect Venice and the lagoon from tides of up to 3 meters. Construction began simultaneously in 2003 at all three lagoon inlets, and the project has been completed in 2014. Floods have caused damage since ancient times and have become more frequent and intense as a result of the combined effect of eustatism (a rise in sea level) and subsidence (a drop in land level) caused by natural and man-induced phenomena. Nowadays, towns and villages in the lagoon are about 23 cm lower with respect to the water level than at the beginning of the 1900s. Each year, floods can cause serious problems for the inhabitants as well as deterioration of architecture, urban structures and the ecosystem. Over the entire lagoon area, there is also a constant risk of a catastrophic event such as that of 4 November 1966, when a tide of 194 cm submerged Venice, Chioggia and the other built-up areas

Design and Characterization of a Small-Scale Solar Sail Prototype by Integrating NiTi SMA and Carbon Fibre Composite

Solar sails are propellantless systems where the propulsive force is given by the momentum exchange of reflecting photons. In this study, a self-deploying system based on NiTi shape memory wires and sheets has been designed and manufactured. A small-scale prototype of solar sail with carbon fibre loom has been developed. Different configurations have been tested to optimize material and structure design of the small-scale solar sail. In particular the attention has been focused on the surface/weight ratio and the deployment of the solar sail. By reducing weight and enlarging the surface, it is possible to obtain high values of characteristic acceleration that is one of the main parameters for a successful use of the solar sail as propulsion system. Thanks to the use of shape memory alloys for self-actuation of the system, complexity of the structure itself decreases. Moreover, sail deployment is simpler

Prediction of Cracking Induced by Indirect Actions in RC Structures

Cracking of concrete plays a key role in reinforced concrete (RC) structures design, especially in serviceability conditions. A variety of reasons contribute to develop cracking and its presence in concrete structures is to be considered as almost unavoidable. Therefore, a good control of the phenomenon in order to provide durability is required. Cracking development is due to tensile stresses that arise in concrete structures as a result of the action of direct external loads or restrained endogenous deformations. This paper focuses on cracking induced by indirect actions. In fact, there is very limited literature regarding this particular phenomenon if compared to its high incidence in the construction practice. As a consequence, the correct prediction of the crack opening, width and position when structures are subjected to imposed deformations, such as massive castings or other highly restrained structures, becomes a compelling task, not so much for the structural capacity, as for their durability. However, this is only partially addressed by commonly used design methods, which are usually intended for direct actions. A set of non-linear analysis on simple tie models is performed using the Finite Element Method in order to study the cracking process under imposed deformations. Different concrete grades have been considered and analysed. The results of this study have been compared with the provisions of the most common codes

Influence of Slenderness on the Evaluation of Epistemic Uncertainty Related to Non-Linear Numerical Analysis of RC Columns

This investigation is devoted to quantify the epistemic uncertainty related to the nonlinear analysis of reinforced concrete columns characterized by high slenderness using numerical codes. The adoption of refined numerical tools, which are able to consider both mechanical and geometric non linearities, implies to perform assumptions and approximations with respect to reality. Whit reference to reliability analysis, these simplifications lead, inevitably, to additional uncertainties which are of epistemic nature. In fact, these uncertainties may be reduced by the engineers/analysts by increasing the level of refinement of the numerical model and/or increasing knowledge about parameters associated to material models. However, also numerical model established by expert engineers/analysts are affected by this kind of epistemic uncertainty. Accepting that the level of uncertainty associated to the experimental tests set are minimized, the epistemic uncertainty associated to non-linear numerical simulations can be quantified characterizing the model uncertainty random variable comparing the outcomes of numerical results to the associated experimental ones. The present investigation proposes the quantification of the model uncertainty related to non-linear numerical simulations of slender RC columns. A total number of 40 experimental results known from literature are herein selected in coherence with current Eurocodes specifications. The experiments are reproduced adopting non-linear numerical analysis differentiating between several modelling hypotheses (i.e., numerical code; materials models). The comparison between experimental and numerical results is adopted to characterize the most suitable probabilistic model for the model uncertainty random variable associated to non-linear numerical simulations of RC columns subjected to significant slenderness. The outcomes of the research are useful to provide background to the characterization of partial safety factor for model uncertainty in non-linear numerical analysis using the approach of the global resistance format for safety verifications

Seismic Upgrading of Existing Reinforced Concrete Buildings Using Friction Pendulum Devices: A Probabilistic Evaluation

In many countries around the world a huge number of existing reinforced concrete (RC) structures have been realized without account for seismic detailing, even if they are located in areas subjected to high seismicity. In this context, several passive seismic protection techniques have been developed and applied to retrofit these structures such as, for an example, seismic isolation. The aim of this work is to characterize in probabilistic terms the seismic performance of a framed RC building retrofitted by means of sliding friction pendulum (FPS) devices. Specifically, the response of an existing RC building located in a high seismicity area in Italy is investigated. After the description of the main available information about the structure, a non-linear numerical model has been defined by means of fiber-elements approach. Then, non-linear dynamic analyses considering multiple recorded ground motions with the three accelerometric components have been carried out to assess the seismic response of the building with and without the retrofitting intervention composed of FPS isolators. Finally, the results are processed to achieve a probabilistic assessment of the seismic performance of the retrofitting intervention

Physical exercise and oxidative stress in muscular dystrophies: is there a good balance? Exercise and oxidative stress in MDs

The effect of oxidative stress on muscle damage inducted by physical exercise is widely debated. It is generally agreed that endurance and intense exercise can increase oxidative stress and generate changes in antioxidant power inducing muscle damage; however, regular and moderate exercise can be beneficial for the health improving the antioxidant defense mechanisms in the majority of cases. Growing evidences suggest that an increased oxidative/nitrosative stress is involved in the pathogenesis of several muscular dystrophies (MDs). Notably, physical training has been considered useful for patients with these disorders. This review will focus on the involvement of oxidative stress in MDs and on the possible effects of physical activities to decrease oxidative damage and improve motor functions in MDs patients

The proposal of a clinical protocol to assess central and peripheral fatigue in myotonic dystrophy type 1

DM1 is an autosomal-dominant disorder characterized by muscle weakness, myotonia, and multisystemic involvement. According to current literature fatigue and daytime sleepiness are among the main symptoms of DM1. Oxidative stress has been proposed to be one of the pathogenic factors of fatigue consequent to DM1. In this study, we investigated the dimensions of experienced fatigue and  physiological fatigue in a sample of 26 DM1 patients (17 males, 9 females, mean age 41.6 years, SD±12.7); experienced fatigue has been studied through Fatigue Severity Scale (FSS), and physiological fatigue was measured through an intermittent incremental exercise of the forearm muscles using a myometer; oxidative stress balance markers trend during aerobic exercise test have been collected. The occurrence of central fatigue in the sample means that central activation worsens during the motor contraction; interestingly FSS score was significantly correlated to MVC (before and after the effort, r-before=-0.583, p<0.01, r-after= -0.534, p<0.05), and to motor disability measured by MRC (r=-0.496, p<0.05); moreover we found a strong tendency towards significance in the association to lactate baseline (r=0.378, p=0.057).Results are discussed to define whether or not, based on clinical and laboratory grounds, such exercise training protocol may be suitable for proper management of DM1 patients; proper assessment of fatigue should be included in algorithms for data collection in DM1 patient registries