Strength and ductility of corroded strands within the framework of safety assessment of existing bridges

Existing bridges built in the last 50 years face challenges due to states far different than those envisaged when they were designed, due to increased loads, ageing of materials, and poor maintenance. For post-tensioned bridges, the need emerged for reliable engineering tools for the evaluation of their capacity in case of steel corrosion due to lack of mortar injection. This can lead to sudden brittle collapses, highlighting the need for proper maintenance and monitoring. This thesis proposes a peak strength model for corroded strands, introducing a “group coefficient” that aims at considering corrosion variability in the wires constituting the strands. The application of the introduced model in a deterministic approach leads to the proposal of strength curves for corroded strands, which represent useful engineering tools for estimating their maximum strength considering both geometry of the corrosion and steel material parameters. Together with the proposed ultimate displacement curves, constitutive laws of the steel material reduced by the effects of corrosion can be obtained. The effects of corroded strands on post-tensioned beams can be evaluated through the reduced bending moment-curvature diagram accounting for these reduced stress-strain relationships. The application of the introduced model in a probabilistic approach allows to estimate peak strength probability functions and consecutive design-oriented safety factors to consider corrosion effects in safety assessment verifications. Both approaches consider two procedures that are based on the knowledge level of the corrosion in the strands. On the sidelines of this main research line, this thesis also presents a study of a seismic upgrading intervention of a case-study bridge through HDRB isolators providing a simplified procedure for the identification of the correct device. The study also investigates the effects due to the variability of the shear modulus of the rubber material of the HDRB isolators on the structural response of the isolated bridge.

Analytical methods for modeling elastic metasurfaces

This dissertation aims at developing advanced analytical tools able to model surface waves propagating in elastic metasurfaces. In particular, four different objectives are defined and pursued throughout this work to enrich the description of the metasurface dynamics. First, a theoretical framework is developed to describe the dispersion properties of a seismic metasurface composed of discrete resonators placed on a porous medium considering part of it fully saturated. Such a model combines classical elasticity theory, Biot’s poroelasticity and an effective medium approach to describe the metasurface dynamics and its coupling with the poroelastic substrate. Second, an exact formulation based on the multiple scattering theory is developed to extend the two-dimensional classical Lamb’s problem to the case of an elastic half-space coupled to an arbitrary number of discrete surface resonators. To this purpose, the incident wavefield generated by a harmonic source and the scattered field generated by each resonator are calculated. The substrate wavefield is then obtained as solutions of the coupled problem due to the interference of the incident field and the multiple scattered fields of the oscillators. Third, the above discussed formulation is extended to three-dimensional contexts. The purpose here is to investigate the dynamic behavior and the topological properties of quasiperiodic elastic metasurfaces. Finally, the multiple scattering formulation is extended to model flexural metasurfaces, i.e., an array of thin plates. To this end, the resonant plates are modeled by means of their equivalent impedance, derived by exploiting the Kirchhoff plate theory. The proposed formulation permits the treatment of a general flexural metasurface, with no limitation on the number of plates and the configuration taken into account. Overall, the proposed analytical tools could pave the way for a better understanding of metasurface dynamics and their implementation in engineered devices.

Sustainable pavements for rural scenarios: laboratory and in-situ characterization of recycled materials and innovative construction solutions

Growing need for infrastructure has led to expanding research on advances in road pavement materials. Finding solutions that are sustainable, environmentally friendly and cost-efficient is a priority. Focusing such efforts on low-traffic and rural roads can contribute with a significant progress in the vital circulatory system of transport for rural and agricultural areas. An important alternative material for pavement construction is recycled aggregates from solid wastes, including waste from civil engineering activities, mainly construction and demolition. A literature review on studies is made; it is performed a planned set of laboratory testing procedures aimed to fully characterize and assess the potential in-situ mechanical performance and chemical impact. Furthermore, monitoring the full-scale response of the selected materials in a real field construction site, including the production, laying and compaction operations. Moreover, a novel single-phase solution for the construction of semi-flexible paving layers to be used as alternative material to common concrete and bituminous layers is experimented and introduced, aiming the production and laying of a single-phase laid material instead of a traditional two phases grouted macadam. Finally, on a parallel research work for farming pavements, the possible use of common geotechnical anti-erosive products for the improvement of soil bearing capacity of paddock areas in cattle husbandries of bio-farms is evaluated. this thesis has clearly demonstrated the feasibility of using the sustainable recycled aggregates for low-traffic rural roads and the pavements of farming and agriculture areas. The pavement layers constructed with recycled aggregates provided satisfying performance under heavy traffic conditions in experimental pavements. This, together with the fact that these aggregates can be available in most areas and in large quantities, provides great impetus towards shifting from traditional materials to more sustainable alternatives. The chemical and environmental stability of these materials proves their soundness to be utilized in farming environments.

Intervista camminata e altri metodi qualitativi per monitorare l'efficacia dei progetti di Educazione Avventura con adolescenti a rischio

INTRODUZIONE - La presente ricerca è incentrata sul monitoraggio dell’efficacia dei progetti di Educazione Avventura con adolescenti difficili, in particolare del progetto “Lunghi cammini educativi”. A partire da un’analisi della letteratura sull’educazione esperienziale nature-based e in particolare sull’Adventure Education con adolescenti difficili, è stata progettata una rilevazione empirica attraverso cui sperimentare un metodo di monitoraggio finalizzato a cogliere la dimensione processuale (che nella ricerca nell’ambito resta spesso inesplorata, poiché sono maggiormente diffusi i metodi di monitoraggio cosiddetti “black-box”), utilizzando un sistema integrato di diverse tecniche di rilevazione. Le due principali domande che hanno guidato la ricerca sono state: 1.Quali processi educativi significativi si innescano e possono essere osservati durante l’esperienza? 2.Il metodo dell’intervista camminata, integrato ad altri metodi, è utile per individuare e monitorare questi processi? METODO - Collocandosi all’interno di un framework metodologico qualitativo (influenzato da riflessioni post-qualitative, paradigma delle mobilità e sguardo fenomenologico), la ricerca prende la forma di uno studio di caso singolo con due unità di analisi, e prevede la triangolazione di diversi metodi di raccolta dei dati: analisi documentale; osservazione partecipante nei cammini e nelle riunioni di équipe; interviste (prima, durante, dopo il cammino) con differenti tecniche: camminata, “image-elicited”, tradizionale, online. RISULTATI - L’analisi tematica abduttiva delle interviste e delle osservazioni conferma quanto già evidenziato dalla letteratura circa la centralità della dilatazione del campo d’esperienza e del lavoro su alcune life skills (in particolare, competenze personali e growth mindset). Emergono anche alcuni key findings inattesi: il notevole “peso” dello stile educativo dell’accompagnatore; la “scoperta” del ruolo della quotidianità all’interno dell’esperienza straordinaria; la necessità di consapevolezza riguardo al potenziale educativo dell’ambiente (naturale e/o antropizzato), per una maggiore intenzionalità nelle scelte strategiche di cammino. L’intervista camminata, nonostante alcuni limiti, si conferma come metodo effettivamente utile a cogliere la dimensione processuale, e coerente con il contesto indagato.

Sensor networks optimization and software development for Structural Health Monitoring based on ultrasonic guided waves

The Structural Health Monitoring (SHM) research area is increasingly investigated due to its high potential in reducing the maintenance costs and in ensuring the systems safety in several industrial application fields. A growing demand of new SHM systems, permanently embedded into the structures, for savings in weight and cabling, comes from the aeronautical and aerospace application fields. As consequence, the embedded electronic devices are to be wirelessly connected and battery powered. As result, a low power consumption is requested. At the same time, high performance in defects or impacts detection and localization are to be ensured to assess the structural integrity. To achieve these goals, the design paradigms can be changed together with the associate signal processing. The present thesis proposes design strategies and unconventional solutions, suitable both for real-time monitoring and periodic inspections, relying on piezo-transducers and Ultrasonic Guided Waves. In the first context, arrays of closely located sensors were designed, according to appropriate optimality criteria, by exploiting sensors re-shaping and optimal positioning, to achieve improved damages/impacts localisation performance in noisy environments. An additional sensor re-shaping procedure was developed to tackle another well-known issue which arises in realistic scenario, namely the reverberation. A novel sensor, able to filter undesired mechanical boundaries reflections, was validated via simulations based on the Green's functions formalism and FEM. In the active SHM context, a novel design methodology was used to develop a single transducer, called Spectrum-Scanning Acoustic Transducer, to actively inspect a structure. It can estimate the number of defects and their distances with an accuracy of 2[cm]. It can also estimate the damage angular coordinate with an equivalent mainlobe aperture of 8[deg], when a 24[cm] radial gap between two defects is ensured. A suitable signal processing was developed in order to limit the computational cost, allowing its use with embedded electronic devices.

Trapianto di polmone ed ex-vivo. Esperienza iniziale in due centri trapianti di polmone

Background Il trapianto polmonare rappresenta l'unica soluzione percorribile per l'insufficienza respiratoria end-stage. La principale limitante ad un suo impiego è rappresentata dalla scarsità di polmoni idonei. In questo contesto si colloca il progetto di ricondizionamento ex-vivo. L'implementazione risulta possibile attraverso il ricondizionamento di organi cosiddetti “marginali” o giudicati inizialmente non idonei al trapianto e da donatori a cuore fermo (Donor after Cardiac Death – DCD). Scopo Lo scopo principale del progetto è quello di analizzare i risultati a breve e medio termine del trapianto polmonare effettuato impiegando polmoni sottoposti a procedura di ricondizionamento ex-vivo in due centri trapianti di polmone a basso volume. Materiali e Metodi I dati sono stati raccolti retrospettivamente (da Giugno 2013 per quanto riguarda l’ISMETT e dal 2014 quelli dell’ Ospedale S. Orsola-Malpighi) e in maniera prospettica dal 2019. Risultati Sommando i dati relativi ad entrambi i centri, dal 2013 sono stati eseguiti un totale di 26 procedure di riperfusione. Sei volte i polmoni sono stati giudicati idonei al trapianto al termine con 5 trapianti doppi e un trapianto singolo sinistro. I risultati in termine di sopravvivenza a medio termine sono risultati sovrapponibili a quelli disponibili in letteratura, tuttavia è stato registrato un alto tasso di PGD (Primary Graft Disfunction) di grado 3, da imputare alla patologia di base del ricevente (ipertensione polmonare), che per protocollo di istituto rimane con supporto cardio-respiratorio (ECMO) dopo il trapianto. Conclusioni L’EVLP si conferma in centri di piccolo e medio volume un metodo sicuro ed efficace per implementare in numero di polmoni idonei al trapianto.

Analysis of the long-term subsidence in the urban area of Bologna

Land subsidence in urban areas represents a widespread geological hazard and a pressing challenge for modern society. This research focuses on the subsidence process affecting the city of Bologna (Italy). Since the 1960s, Bologna has experienced ground deformation due to aquifers overexploitation that peaked during the 1970s with rates of 10 cm/year. Despite a general reduction in these rates over the subsequent decades, thanks to groundwater regulations policies, recent data underscore a substantial subsidence resurgence. To reconstruct the subsurface stratigraphic architecture of Bologna’s urban area and generate a 3D geological model, a multidisciplinary approach centred on a stratigraphic analysis relying on the lithofacies criterion was adopted. The convergence of the analyses within this framework resulted in partitioning the study area into three geological domains exhibiting unique morphological features and depositional stacking patterns. Subsequently, since long-term data are crucial for a comprehensive understanding of ongoing subsidence, a methodology was developed to generate cumulative ground displacement time series and maps by integrating ground-based and remotely-sensed measurements. While the reconstructed long-term subsidence field consistently aligns with the primary geological variations summarised in the 3D model, the generated cumulative displacement curves systematically match pluriannual trends observed in groundwater level and pumping monitoring data. Lastly, to evaluate the expression of the observed relationships from a geotechnical perspective, a series of one-dimensional subsidence calculations were conducted considering the mechanical properties of the investigated deposits and piezometric data. These analyses provided valuable insight into the overall mechanical behaviour of the existing soils, as well as the post-pumping groundwater level and pore pressure distributions, consistent with field data. The methodological approach employed enables a comprehensive analysis of land subsidence in urban areas, allowing the exploration of individual factors governing the deformation process and their interactions, even within complex stratigraphic and hydrogeological environments such as Bologna’s urban area.

Promuovere l'autovalutazione e il miglioramento delle strategie di apprendimento degli studenti internazionali cinesi: una ricerca empirica presso l'Università di Bologna

Nel quadro di alcuni filoni di ricerca inerenti alla promozione delle strategie cognitive, metacognitive e motivazionali degli studenti per una migliore efficacia del loro apprendimento (anche a livello universitario), il contributo presenta l’impianto e gli esiti di una ricerca empirica volta a indagare le percezioni degli studenti internazionali cinesi sulla loro esperienza universitaria in Italia, con un focus sulle eventuali difficoltà nell’adozione di un approccio autonomo e strategico all’apprendimento, e a sperimentare un intervento formativo messo a punto per sostenerli nel miglioramento del loro approccio all’apprendimento attraverso l’uso di procedure sistematiche di autoriflessione, self-recording e autovalutazione supportate dalla ricercatrice. Il disegno della ricerca è un quasi-esperimento a due gruppi con pre-test e post-test. Il campione è costituito da 60 studenti di diversi Dipartimenti dell’Università di Bologna che hanno partecipato volontariamente alla ricerca, di cui 30 hanno preso parte all’intervento. Gli strumenti utilizzati per la misurazione in ingresso e in uscita sono il Questionario sui Processi di Apprendimento e alcune scale del Questionario sulle Strategie di Apprendimento. Agli studenti del gruppo sperimentale è stato somministrato anche un questionario finale di valutazione del percorso formativo. Sono state inoltre effettuate alcune interviste a distanza di tempo come fase di follow up. Gli studenti in entrambi i gruppi affrontano sfide relative all’ambientamento nel contesto universitario italiano, con particolare riferimento a difficoltà linguistiche e di integrazione sociale. I principali fattori influenti sull’efficacia dello studio includono le barriere linguistiche, la gestione del tempo, la consapevolezza e l’uso delle strategie di studio. Nonostante emerga un miglioramento del gruppo sperimentale tra pre e post test, le differenze tra i due gruppi non sono risultate statisticamente significative. Tuttavia, i feedback forniti dagli studenti nel questionario di soddisfazione per il percorso formativo e nelle interviste post-intervento evidenziano percezioni positive sull’utilità del percorso, con benefici relativi al loro approccio allo studio.