Risikobewertung von Brücken, die zu wirbelerregten Schwingungen neigen

The present dissertation deals with the risk assessment of bridge decks prone to vortex induced vibrations (VIV), which is presently recognized as a key issue in the design of flexible bridges. A procedure is proposed to quantify the risk associated with VIV of bridge decks. The framework adopted is in line with the general risk management framework developed by the IGC 802. Performance-based-design approach is followed and the risk is quantified by using a modified version of the PEER equation. First, the hazard analysis is developed. It consists in evaluating the probability of the hazard (wind speed and direction) by means of Weibull distribution. The wind data are also analyzed by using a hybrid model, which consists of estimating the model parameters without considering wind calms. The results are compared with those obtained through the classical approach. In the second part of the dissertation the structural vulnerability analysis is conducted. It evaluates the probability of the structural response during VIV. A careful revision of the state of the art is firstly reported on both the phenomenological aspects and mathematical modeling of VIV of bluff bodies. It led to the conclusion that no model is able to provide reliable predictions of the structural response at values of the Scruton number different from that at which the aeroelastic parameters are estimated. In this work, the Ehsan-Scanlan model (E-S model) was studied in depth because it is considered suitable for practical applications to bridge decks. Wind tunnel tests were performed to apply E-S model to a idealized case study. Highlighted in this analysis is the physical coherence of the van der Pol-type equation used to model VIV of structures prone to wind excitation. Even though the validity of the identification procedure employed in E-S model to determine the aeroelastic parameters of the model is demonstrated, a limit of the procedure is observed when the limit-cycle oscillation amplitude is estimated from experimental signals. In addition, an alternative identification procedure is proposed based on the direct numerical solution of the nonlinear differential equation. In the third part of the dissertation the application of the developed procedure to a case study is reported. The effects in terms of risk due to the different assumptions standing behind the procedure are highlighted. Finally, the perspectives of future developments of this research work are discussed.Die vorliegende Arbeit beschäftigt sich mit der Risikobewertung von Brücken, bei denen unter Windanströmung wirbelerregte Schwingungen auftreten. Eine Untersuchung der Tragwerksantwort unter der speziellen Windbelastung wird gegenwärtig als unerlässlich beim Entwurf von schlanken Brücken angesehen. Zur Quantifizierung des Risikos im Zusammenhang mit wirbelerregten Schwingungen wird ein Ansatz vorgestellt, der sich an die bekannte PEER-Gleichung anlehnt. Im ersten Schritt wird die Gefährdung des Standorts der Brücke ermittelt. Dabei werden die Auftretenswahrscheinlichkeiten der Windereignisse für den Standort analysiert. Sowohl für die Windgeschwindigkeit als auch für die Windrichtung wird eine Weilbull-Verteilung angenommen. Die Winddaten werden auch mit einem Hybridmodell untersucht, wobei die Modellparameter ohne die Berücksichtigung von windstillen Zeiträumen bestimmt werden. Die Ergebnisse beider Verfahren werden verglichen. Im nächsten Schritt wird die Schwingungsreaktion des Bauwerks auf die Anregung durch den Wind bewertet. Wie eine Literaturrecherche zeigt, ist keines der aus dem Fachschrifttum bekannten Modelle in der Lage, zuverlässig das Schwingungsverhalten der Brücke für Scruton-Zahlen vorherzusagen, für die nicht die aeroelastischen Parameter identifiziert wurden. Das Ehsan-Scanlan-Modell liefert jedoch brauchbare Ergebnisse für praktische Anwendungen im Brückenbau und wird deshalb hier verwendet. Die numerische Lösung der auftretenden Van-der-Pol-Gleichung wird mit speziell dazu durchgeführten Windkanalmessungen verglichen. Auftretende Probleme bei der Ermittlung der Amplituden der Grenzzyklen werden ausführlich diskutiert. Zusätzlich wird eine alternative Vorgehensweise zur Bestimmung der aeroelastischen Parameter des Ehsan-Scanlan-Modells vorgestellt. In einer Fallstudie werden die Möglichkeiten des entwickelten Verfahrens zur Risikobewertung verdeutlicht. Abschließend wird ein Ausblick für weitere Entwicklungen in diesem Forschungsgebiet vorgestellt

Natural thermal plasters for fibre-composite matrices. Structural-energy-environmental analysis

The article presents the first results of MIRACLE research, aimed at designing, testing, and implementing innovative reinforcement systems with bio-composite matrix, with additives containing natural thermal-plasters, usable in the restoration of residential buildings created before 1945. Starting from a brief description of the properties of fibre-reinforced cement organic matrices, supported by a survey of international research aimed at developing innovative methodologies, systems, and components used to improve the energy and mechanical performances of listed historic buildings, the most suitable thermal-plasters will be analysed (among those existing on the Italian market), identifying the performance characteristics both in terms of mechanic and thermal and environmental sustainability

Assessment of Body Composition in Health and Disease Using Bioelectrical Impedance Analysis (BIA) and Dual Energy X-Ray Absorptiometry (DXA): A Critical Overview

The measurement of body composition (BC) represents a valuable tool to assess nutritional status in health and disease. The most used methods to evaluate BC in the clinical practice are based on bicompartment models and measure, directly or indirectly, fat mass (FM) and fat-free mass (FFM). Bioelectrical impedance analysis (BIA) and dual energy X-ray absorptiometry (DXA) (nowadays considered as the reference technique in clinical practice) are extensively used in epidemiological (mainly BIA) and clinical (mainly DXA) settings to evaluate BC. DXA is primarily used for the measurements of bone mineral content (BMC) and density to assess bone health and diagnose osteoporosis in defined anatomical regions (femur and spine). However, total body DXA scans are used to derive a three-compartment BC model, including BMC, FM, and FFM. Both these methods feature some limitations: the accuracy of BIA measurements is reduced when specific predictive equations and standardized measurement protocols are not utilized whereas the limitations of DXA are the safety of repeated measurements (no more than two body scans per year are currently advised), cost, and technical expertise. This review aims to provide useful insights mostly into the use of BC methods in prevention and clinical practice (ambulatory or bedridden patients). We believe that it will stimulate a discussion on the topic and reinvigorate the crucial role of BC evaluation in diagnostic and clinical investigation protocols

Clinical staff work sampling in a neurorehabilitation hospital and its relationship to severity of disease

AIM: Study aimed to analyse how rehabilitation staff spends working time on specific activities in a neurorehabilitation hospital and to determine the number of direct activities received by patients with different levels of disease severity. BACKGROUND: Few studies have investigated how clinical staff spends their time on activities in rehabilitation hospitals without considering at the same time all working categories and without reporting the number of direct activities received by patients with respect to their disease severity. DESIGN: Self-reported observational study. METHOD: Work Sampling Technique was used to record direct, indirect, unit-related and personal activities every 5 min for 2 days. RESULTS: Total of 6,974 activities were recorded over 581 working hours. Physiotherapists and nurses spent 75.2% and 54.8% of their time in direct activities and medical doctors only 25.4%. Total time of direct activities was significantly different among worker categories (p = 0.001) and depended on patients' disease severity (p = 0.020) in a different manner among worker categories (interaction: p = 0.010). This time ranged from almost 4 hr up to 6\ubd hr for the most severely affected patients. CONCLUSION: Type of work differed among professionals. Workload greatly depended on degree of patients' disability. IMPLICATIONS FOR NURSING MANAGEMENT: Nurses and therapists spent most of their time in direct activities with patients. Economic burden of neurorehabilitation may vary greatly depending on disease severity