INDAGINI TEORICHE E SPERIMENTALI SU PARETI SISMICHE IN ACCIAIO

La memoria riguarda il comportamento di pannelli sottili in acciaio utilizzati come pareti di controvento. Per tali sistemi sono previsti due tipi fondamentali di utilizzo: come elementi dissipativi e irrigidenti;come elementi irrigidenti. Il primo caso riguarda pannelli dotati di robusti irrigidimenti, tali da determinare lo snervamento delle lastre costituenti il pannello prima dell’insorgere di fenomeni di instabilità. Tale tipologia è stata utilizzata prevalentemente in Giappone. La tendenza ad adottare pannelli sottili, per i quali l’instabilità avviene in campo elastico, si è sviluppata prevalentemente negli USA ed in Canada, ove attraverso indagini sperimentali si è constatato il not…

Advanced Signal Processing for Ultrasonic Structural Monitoring of Waveguides, in Bridge Maintenance, Safety Management, Health Monitoring and Informatics

Ultrasonic Guided Waves (UGWs) are a useful tool in those structural health monitoring applications that can benefit from built-in transduction, moderately large inspection ranges and high sensitivity to small flaws. This paper describes a damage detection method, based on wavelet transform and outlier analysis for structural waveguides. The method combines the advantages of UGW inspection with the outcomes of the Discrete Wavelet Transform (DWT) that is used for extracting defect-sensitive features that can be combined to perform a multivariate diagnosis of damage. In particular, the DWT is exploited to generate a set of relevant wavelet coefficients to construct a uni-dimensional or multi…

Ultrasonic Guided Waves-Based Monitoring of Rail Head: Laboratory and Field Tests

Recent train accidents have reaffirmed the need for developing a rail defect detection system more effective than that currently used. One of the most promising techniques in rail inspection is the use of ultrasonic guided waves and noncontact probes. A rail inspection prototype based on these concepts and devoted to the automatic damage detection of defects in rail head is the focus of this paper. The prototype includes an algorithm based on wavelet transform and outlier analysis. The discrete wavelet transform is utilized to denoise ultrasonic signals and to generate a set of relevant damage sensitive data. These data are combined into a damage index vector fed to an unsupervised learning…

ULTRASONIC WAVES IN HETEROGENEOUS MATERIALS - MECHANICAL CHARACTERIZATION OF HETEROGENEOUS MATERIALS BY MEANS OF ULTRASONIC TESTS AND NUMERICAL MODELS: THE CONCRETE THE CONCRETE

This Ph.D thesis treats the propagation of ultrasonic waves in heterogeneous materials. It is widely known how waves propagate in homogeneous materials like metallic ones. But very few aspects are known about the propagation in the heterogeneous materials because of the complex behavior regarding these materials. The heterogeneity can be related with the intrinsic properties, elastic and chemical, of each phase of the material, or with the periodic or random arrangement of inclusions of constant or different shapes. Concrete is a common case. In this work the first chapter gives a description of the main characteristics of heterogeneous materials.. In the second one, the methods of inspecti…

Molecular Dynamic Simulation on Polyamide6/Graphene nano-layers nanocomposites

In this work results obtained from Molecular Dynamic Simulation (MDS) on Polyamide 6 (PA6) chains in graphene containing nanocomposites are presented. Through detailed MDS, the interface of complex nanocomposites systems can be fully characterized, furthermore different physical properties, such as density, end-to-end distance , and average radius of gyration of polymers chains can be predicted. This issue is useful for the design of highly value-added nanocomposites and the optimization of their production process, by defining transformation steps and status variables (temperature, time and pressure), that can also help the industrial production.

Ultrasonic Guided Waves-Based Monitoring of Rail Head: Laboratory and Field Tests in Advances in Civil Engineering

Recent train accidents have reaffirmed the need for developing a rail defect detection system more effective than that currently used. One of the most promising techniques in rail inspection is the use of ultrasonic guided waves and noncontact probes. A rail inspection prototype based on these concepts and devoted to the automatic damage detection of defects in rail head is the focus of this paper. The prototype includes an algorithm based on wavelet transform and outlier analysis. The discrete wavelet transform is utilized to denoise ultrasonic signals and to generate a set of relevant damage sensitive data. These data are combined into a damage index vector fed to an unsupervised learning…

MECHANICAL RESPONSE OF BERNULLI EULER BEAMS ON FRACTIONAL ORDER ELASTIC FOUNDATION

An unsupervised Learning Algorithm for Fatigue Crack Detection in Waveguides

Ultrasonic guided waves (UGWs) are a useful tool in structural health monitoring (SHM) applications that can benefit from built-in transduction, moderately large inspection ranges, and high sensitivity to small flaws. This paper describes an SHM method based on UGWs and outlier analysis devoted to the detection and quantification of fatigue cracks in structural waveguides. The method combines the advantages of UGWs with the outcomes of the discrete wavelet transform (DWT) to extract defect-sensitive features aimed at performing a multivariate diagnosis of damage. In particular, the DWT is exploited to generate a set of relevant wavelet coefficients to construct a uni-dimensional or multi-di…

Digital signal processing for rail monitoring by means of ultrasonic guided waves

Recent train accidents have reaffirmed the need for developing rail defect detection systems that are more effective than those used today. One of the recent developments in rail inspection is the use of ultrasonic guided waves (UGWs) and non-contact probing techniques to target transverse-type defects. Besides the obvious advantages of non-contact probing, that include robustness and a potential for large inspection speed, such a system can theoretically detect transverse defects under horizontal shelling or head checks. This paper demonstrates the effectiveness of digital signal processing to enhance the damage detection sensitivity of the non-contact system. The method proposed here comb…

Rheological Percolation Threshold in High-Viscosity Polymer/CNTs Nanocomposites

AbstractPolystyrene (PS)/multi-walled carbon nanotubes (CNT) nanocomposites have been prepared through melt mixing processing aiming at obtaining a uniform and homogeneous dispersion of the used nanoparticles within the polymeric matrix. Optical and scanning electron microscopy has been employed to determine the dispersion and distribution of CNTs at different length scales. Furthermore, the linear viscoelastic behavior of formulated nanocomposites has been deeply investigated. As a result of CNTs added, the nanocomposites experience a transition from liquid-like to solid-like rheological behavior, and a disappearance of relaxation processes at low frequency can be noticed. By plotting G’ v…

Application of principal component analysis and wavelet transform to fatigue crack detection in waveguides

Ultrasonic Guided Waves (UGWs) are a useful tool in structural health monitoring (SHM) applications that can benefit from built-in transduction, moderately large inspection ranges and high sensitivity to small flaws. This paper describes a SHM method based on UGWs, discrete wavelet transform (DWT), and principal component analysis (PCA) able to detect and quantify the onset and propagation of fatigue cracks in structural waveguides. The method combines the advantages of guided wave signals processed through the DWT with the outcomes of selecting defect-sensitive features to perform a multivariate diagnosis of damage. This diagnosis is based on the PCA. The framework presented in this paper …

Advanced Ultrasonic Structural Monitoring of Waveguides

Ultrasonic Guided Waves (UGWs) are a useful tool in those structural health monitoring applications that can benefit from built-in transduction, moderately large inspection ranges and high sensitivity to small flaws. This paper describes two methods, based on linear and nonlinear acoustics for structural damage detection based on UGWs. The linear method combine the advantages of UGW inspection with the outcomes of the Discrete Wavelet Transform (DWT) that is used for extracting defect-sensitive features that can be combined to perform a multivariate diagnosis of damage. In particular, the DWT is exploited to generate a set of relevant wavelet coefficients to construct a uni-dimensional or m…

Bi-layered polyurethane – Extracellular matrix cardiac patch improves ischemic ventricular wall remodeling in a rat model

As an intervention to abrogate ischemic cardiomyopathy, the concept of applying a temporary, local patch to the surface of the recently infarcted ventricle has been explored from a number of design perspectives. Two important features considered for such a cardiac patch include the provision of appropriate mechanical support and the capacity to influence the remodeling pathway by providing cellular or biomolecule delivery. The objective of this report was to focus on these two features by first evaluating the incorporation of a cardiac extracellular matrix (ECM) component, and second by evaluating the impact of patch anisotropy on the pathological remodeling process initiated by myocardial …

COMPORTAMENTO DI IMPALCATI DA PONTE A CASSONE IN ACCIAIO-CALCESTRUZZO CON ANIMA ONDULATA

La memoria riguarda il comportamento di un impalcato di ponte stradale a cassone avente le anime sagomate secondo una sinusoide, con soletta in c.a. collaborante. L'impalcato presenta schema statico longitudinale di trave continua su 4 appoggi. The paper concerns the behaviour of a box-girder bridge deck road having a steel box and a concrete slab. The steel webs are shaped according to a sine wave. The deck has a width of 13.70 m and a length of 182 m, with the longitudinal static scheme as a continuous beam on four supports. The study highlights the reliability of this constructive solution.

TRAVI CONTINUE IN ACCIAIO CON ANIMA ONDULATA PER IMPALCATI MISTI IN ACCIAIO CALCESTRUZZO

La memoria riguarda gli impalcati per ponti stradali con travi in acciaio saldate, aventi l’anima sagomata secondo una sinusoide e soletta in c.a. collaborante. L’attenzione è focalizzata su impalcati aventi schema statico longitudinale di trave continua su 4 appoggi, costituiti da due sole travi in acciaio, e da una soletta in c.a.. Il progetto è sviluppato per un ponte stradale di I categoria, avente larghezza di 12.10 m e lungo 182 m. Lo studio consente di confrontare le soluzioni costruttive rappresentate da travi con anima tradizionale piana o sinusoidale e di porre in luce alcuni vantaggi di tale ultimo sistema.

Outlier analysis and principal component analysis to detect fatigue cracks in waveguides

Ultrasonic Guided Waves (UGWs) are a useful tool in structural health monitoring (SHM) applications that can benefit from built-in transduction, moderately large inspection ranges and high sensitivity to small flaws. This paper describes a SHM method based on UGWs, discrete wavelet transform (DWT), outlier analysis and principal component analysis (PCA) able to detect and quantify the onset and propagation of fatigue cracks in structural waveguides. The method combines the advantages of guided wave signals processed through the DWT with the outcomes of selecting defectsensitive features to perform a multivariate diagnosis of damage. The framework presented in this paper is applied to the de…

Upside-down ship’s kel-shaped vaults as a contemporary design criteria. The case of the Palace of the Dukes of Braganza in Guimarães (Portugal)

A contemporary worldwide trend is exposing the structural elements of a building to create an articulate and complex architecture whose lines of force give robustness, stability and, at the same time, a sort of lightness and frivolity to the entire construction. However, the combination between the visual conception of architecture and the principles of statics is not new to the world of construction. Exposed structure as a design approach may be observed in many historical buildings, either public, religious or private, and in several cultural and geographical areas where exposed structures communicate power, solidity, and rigour along with an instance of economy and lightness. In this wor…