experimental analysis of a composite bridge under high speed train passages

Abstract Evaluation of resonances phenomenon in high-speed railway bridges during train passage is a dominant issue in order to confirm the structural safety of the bridge and the stability of the ballast on bridge deck. The Sesia viaduct, located in the Turin-Milan high-speed rail line, is one of the most investigated high-speed railway bridges. The maximum accelerations and the resonance train speed were predicted while the bridge vibration modes and the effect of adjacent spans on these were estimated through some detailed experimental and numerical investigations. Nevertheless, some important points remain unclear, such as the actual resonance speed and the influence of deck local vibrations. To verify and clarify these issues, experimental dynamic analyzes based on acceleration measurements of the Sesia viaduct under ETR1000 train passages with speed up to 374km/h were conducted in this study. In the measurements, accelerometers were installed not only on steel box girder but also on concrete deck slab in order to identify local vibration modes of deck members so as to estimate their effect on the evaluation of the accelerations. Comparing the maximum accelerations up to 15Hz with various train speeds, the resonance speed corresponding to the first bending mode of the Sesia viaduct was identified. Furthermore, an analysis based on the identification of the natural frequencies clarified that the high-order resonances between passing train and deck local vibration modes have the largest impact on the maximum acceleration up to 30Hz which is the limit used for the verification of ballast stability in the Eurocode

Complex Nanostructures by Pulsed Droplet Epitaxy

What makes three dimensional semiconductor quantum nanostructures so attractive is the possibility to tune their electronic properties by careful design of their size and composition. These parameters set the confinement potential of electrons and holes, thus determining the electronic and optical properties of the nanostructure. An often overlooked parameter, which has an even more relevant effect on the electronic properties of the nanostructure, is shape. Gaining a strong control over the electronic properties via shape tuning is the key to access subtle electronic design possibilities. The Pulsed Dropled Epitaxy is an innovative growth method for the fabrication of quantum nanostructures with highly designable shapes and complex morphologies. With Pulsed Dropled Epitaxy it is possible to combine different nanostructures, namely quantum dots, quantum rings and quantum disks, with tunable sizes and densities, into a single multi‐function nanostructure, thus allowing an unprecedented control over electronic properties

Influence of Local Deck Vibrations on the Evaluation of the Maximum Acceleration of a Steel-Concrete Composite Bridge for a High-Speed Railway

Abstract European design standards have established an upper limit on the deck acceleration of the high-speed railway bridges, however the influence of local vibrations of the deck members is rarely considered when modelling the vibrational responses of bridges. To evaluate how the inclusion of local deck vibrations might influence predictions of the maximum acceleration, detailed measurements were taken from a steel-concrete composite box-girder bridge on the Italian high-speed railway, and a numerical model of the system was developed. Deck vibrations were measured during high-speed train passages at the maximum train speed of 374 km/h, and compared against a numerical model of the vehicle-bridge system. This analysis revealed that the maximum deck acceleration is 1.3 times greater than the acceleration of the bridge girders, because of the sixth- and seventh-order resonance between the deck's local vibration modes and the structure with a train running at high speeds over 300 km/h. Moreover, when considering local deck vibrations in the numerical model, we found that the interaction between transient local rail deformations and the vehicle travelling on the rails can increase the acceleration of the deck through resonance

A Computational fluid dynamics study on the relative motion effects for high speed train crosswind assessment

The effect of the relative motion between a train and the surrounding infrastructure may result in critical scenarios where the infrastructure has a significant effect on the atmospheric wind. This paper analyses using a computational dynamics approach the variation of the aerodynamic force coefficients on the leading vehicle of a high speed train due to the relative motion between the train and the infrastructure. A limited increase (below 10 percent) in force coefficients are calculated and a small decrease (below 7 percent) is observed in the characteristic wind curve computation

On situ vibration-based structural health monitoring of a railway steel truss bridge: a preliminary numerical study.

Railway network is subject to increasing travelling loads and traffic frequency. In addition, since most of the bridges were built in the last century, they are subject to ageing and degradation. It is therefore necessary to develop proper structural health monitoring systems that can support periodical visual inspections. In this context, direct monitoring systems represent an important and promising solution for structural health monitoring purposes. This paper is the result of a numerical study performed on a 3D FE bridge model based on an existing structure: the latter is a Warren truss railway bridge, located in Northern Italy, built few years after the end of the second world war. The purpose of the study is to numerically evaluate the effectiveness in damage detection and localization of different vibration-based techniques. This analysis has been performed for a set of different damage scenarios, suggested by the infrastructure managers

Complex Nanostructures by Pulsed Droplet Epitaxy

What makes three dimensional semiconductor quantum nanostructures so attractive is the possibility to tune their electronic properties by careful design of their size and composition. These parameters set the confinement potential of electrons and holes, thus determining the electronic and optical properties of the nanostructure. An often overlooked parameter, which has an even more relevant effect on the electronic properties of the nanostructure, is shape. Gaining a strong control over the electronic properties via shape tuning is the key to access subtle electronic design possibilities. The Pulsed Dropled Epitaxy is an innovative growth method for the fabrication of quantum nanostructures with highly designable shapes and complex morphologies. With Pulsed Dropled Epitaxy it is possible to combine different nanostructures, namely quantum dots, quantum rings and quantum disks, with tunable sizes and densities, into a single multi‐function nanostructure, thus allowing an unprecedented control over electronic properties