•Deck acceleration measurement up to the train speed of 374 km/h were analyzed.•Global and local vibration modes up to 30 Hz were identified from field tests.•A highly accurate simulation model of ...deck acceleration was constructed.•High-order resonance of deck vibration is the dominant on the maximum acceleration.•Determination method to consider the track deformation is proposed.
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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Display omitted
•New drive-by detection method for resonant bridges in high-speed railway proposed.•Difference in track irregularities for the first and last vehicles used.•Applicability of the ...proposed method verified numerically.•Proposed method applied to track irregularities in Japan’s high-speed railways.•Resonant bridges verified by in-situ bridge response measurements.
Resonance of railway bridges is a matter of major concern in high-speed railways because it reduces riding comfort, damages the attached structures, and decreases the strength of girder bodies. Although this abnormal behavior can be inspected using in situ displacement measurements taken from the ground, its investigation is tedious and, consequently, is very expensive. In this study, authors developed a novel drive-by system for high-speed railways to detect resonant bridges; the difference between two track irregularities at the same position using devices mounted on the first and last vehicles of a train was measured. This is based on the idea that the response of the last vehicle passing through the resonant bridge is attributed to the superposition of track irregularities and abnormal bridge displacement because of resonance mechanisms. However, the response of the first vehicle primarily arises from track irregularities since the resonance phenomenon is not yet sufficiently excited. The Resonance Detection Index (RDI), defined as the difference between the track irregularities measured by the devices mounted on the first and last vehicles, is used to emphasize the component excited by vehicle length to propose a methodology for detecting resonant bridges.
Numerical simulations clarify that bridge span and track irregularity have greater effects on the RDI than either measurement noise or positioning error. Track irregularity may cause the RDI to vary by ± 2 mm depending on vehicle length wave component of the track irregularity. Consequently, this study demonstrates that resonant bridges with spans between 20 and 60 m can be detected using the proposed RDI.
Finally, the proposed method was applied to track irregularity measurements using actual high-speed trains operating in Japan. More than ten bridges, out of more than 800 bridges, were detected as resonant bridges according to RDI. In situ displacement measurements were performed for three of these bridges, demonstrating the presence of resonance phenomenon and thereby validating the proposed method.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
For the Ga-assisted growth of GaAs nanowires on Si(111) substrates by molecular beam epitaxy, growth temperature, As flux, and Ga flux have been systematically varied across the entire window of ...growth conditions that result in the formation of nanowires. A range of GaAs structures was observed, progressing from pure Ga droplets under negligible As flux through horizontal nanowires, tilted nanowires, vertical nanowires, and nanowires without droplets to crystallites as the As flux was increased. Quantitative analysis of the resulting sample morphology was performed in terms of nanowire number and volume density, number yield and volume yield of vertical nanowires, diameter, length, as well as the number and volume density of parasitic growth. The result is a growth map that comprehensively describes all nanowire and parasitic growth morphologies and hence enables growth of nanowire samples in a predictive manner. Further analysis indicates the combination of global Ga flux and growth temperature determines the total density of all objects, whereas the global As/Ga flux ratio independently determines the resultant sample morphology. Several dependencies observed here imply that all objects present on the substrate surface, i.e. both nanowires and parasitic structures, originate from Ga droplets.
We present a novel approach for the growth of GaAs nanowires (NWs) with controllable number density and diameter, which consists of the combination between droplet epitaxy (DE) and self-assisted NW ...growth. In our method, GaAs islands are initially formed on Si(111) by DE and, subsequently, GaAs NWs are selectively grown on their top facet, which acts as a nucleation site. By DE, we can successfully tailor the number density and diameter of the template of initial GaAs islands and the same degree of control is transferred to the final GaAs NWs. We show how, by a suitable choice of V/III flux ratio, a single NW can be accommodated on top of each GaAs base island. By transmission electron microscopy, as well as cathodo- and photoluminescence spectroscopy, we confirmed the high structural and optical quality of GaAs NWs grown by our method. We believe that this combined approach can be more generally applied to the fabrication of different homo- or heteroepitaxial NWs, nucleated on the top of predefined islands obtained by DE.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Rail corrugation is a degradation phenomenon that manifests as a quasi-periodic irregularity on the running surface of the rail. It is a critical problem for urban railway lines because it induces ...ground-borne vibrations transmitted to the buildings near the infrastructure, causing complaints from the inhabitants. A typical treatment to mitigate the rail corrugation problem is the periodic grinding of the rails, performed by dedicated vehicles. The scheduling of rail maintenance is particularly critical because it can be performed only when the service is interrupted. A procedure for the continuous monitoring of rail corrugation is proposed, based on axlebox acceleration measurements. The rail irregularity is estimated from the measured acceleration by means of a frequency domain model of vertical dynamics of the wheel–rail interaction. The results obtained by using two different methods (a state-of-the-art method and a new one) are compared. Finally, the study of the evolution of the power content of the rail irregularity enables the identification of the track sections where corrugation is developing and rail grinding is necessary.
Structural health monitoring of civil infrastructure, such as bridges and buildings, has become a trending topic in the last few years. The key factor is the technological push given by new ...technologies that permit the acquisition, storage, processing and visualisation of data in real time, thus assessing a structure’s health condition. However, data related to anomaly conditions are difficult to retrieve, and, by the time those conditions are met, in general, it is too late. For this reason, the problem becomes unsupervised, since no labelled data are available, and anomaly detection algorithms are usually adopted in this context. This research proposes a novel algorithm that transforms the intrinsically unsupervised problem into a supervised one for condition monitoring purposes. Considering a bridge equipped with N sensors, which measure static structural quantities (rotations of the piers) and environmental parameters, exploiting the relationships between different physical variables and determining how these relationships change over time can indicate the bridge’s health status. In particular, this algorithm involves the training of N models, each of them able to estimate the quantity measured via a sensor by using the others’ N−1 measurements. Hence, the system can be represented by the ensemble of the N models. In this way, for each sensor, it is possible to compare the real measurement with the predicted one and evaluate the residual between the two; this difference can be addressed as a symptom of changes in the structure with respect to the condition regarded as nominal. This approach is applied to a real test case, i.e., Candia Bridge in Italy, and it is compared with a state-of-the-art anomaly detector (namely an autoencoder) in order to validate its robustness.
Full text
Available for:
CEKLJ, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Nowadays, designing and adopting sustainable and greener transport systems is of upmost interest. The European Commission and different EU countries are developing plans and programs—but also ...delivering resources—aimed at the decarbonization of cities and transport by 2030. In this paper, the case study of the city of Brescia, a city of about 200,000 inhabitants located in northern Italy, is addressed. Specifically, a preliminary operational and financial feasibility study is performed assuming the replacement of the entire compressed natural gas (CNG) powered bus fleet of a specific line; the two alternatives considered are battery electric buses (BEBs) and fuel cell electric buses (FCEBs). For the comparison and evaluation of the two alternatives, specific economic parameters of the three alternatives (BEB, FCEB and the current solution CNGB) were considered: CAPEX (CAPital EXpenditure) and OPEX (OPerational EXpenditure). This allowed us to determine the TCO (total cost of ownership) and TCRO (total cost and revenues of ownership) along three annuities (2022, 2025 and 2030). For the BEB alternative, the TCO and TCRO values are between EUR 0.58/km and EUR 0.91/km. In the case of the FCEB solution, the values of TCO and TCRO are between EUR 1.75/km and EUR 2.15/km. Considering the current CNGB solution, the TCO and TCRO values range between EUR 1.43/km and EUR 1.51/km.
This works focuses on a series of experimental tests carried out to investigate overpressures in tunnels due to train crossings. Although the above-mentioned topic is well known and also defined in ...European standards, in the literature full-scale data are lacking, which are useful to validate the numerical codes required in the certification process and are used in train structural dimensioning. In this respect, an extensive full-scale experimental campaign was planned for observing as many test conditions as possible, such as single passages of different trains, two train crossing, different tests speed, and different tunnel characteristics. In detail, the understanding of the pressure wave generation and transmission is deeply enhanced by studying the pressure evolution both on board and at trackside, considering both single train passages or two trains crossings and having the possibility to compare aerodynamic loads on sealed and unsealed trains. Furthermore, the position of sensors, the speed of the train, and the initial conditions within the tunnel have been proven to be fundamental parameters for properly estimating the pressure loads on trains.
In GaAs nanowires grown along the cubic 111c direction, zinc blende and wurtzite arrangements have been observed in their stacking sequence, since the energetic barriers for nucleation are typically ...of similar order of magnitude. It is known that the interplanar spacing of the (111)c Ga (or As) planes in the zinc blende polytype varies slightly from the wurtzite polytype. However, different values have been reported in the literature. Here, the ratio of the interplanar spacing of these polytypes is extracted based on X‐ray diffraction measurements for thin GaAs nanowires with a mean diameter of 18–25 nm. The measurements are performed with a nano‐focused beam which facilitates the separation of the scattering of nanowires and of parasitic growth. The interplanar spacing of the (111)c Ga (or As) planes in the wurtzite arrangement in GaAs nanowires is observed to be 0.66% ± 0.02% larger than in the zinc blende arrangement.
Full text
Available for:
FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
High refractive index glasses are preferred in integrated photonics applications to realize higher integration scale of passive devices. With a refractive index that can be tuned between SiO2 (1.45) ...and a-SiC (3.2), silicon oxycarbide SiOC offers this flexibility. In the present work, silicon oxycarbide thin films from 0.1 – 2.0 μm thickness are synthesized by reactive radio frequency magnetron sputtering a silicon carbide SiC target in a controlled argon and oxygen environment. The refractive index n and material extinction coefficient k of the silicon oxycarbide films are acquired with variable angle spectroscopic ellipsometry over the UV-Vis-NIR wavelength range. Keeping argon and oxygen gases in the constant ratio, the refractive index n is found in the range from 1.41 to 1.93 at 600 nm which is almost linearly dependent on RF power of sputtering. The material extinction coefficient k has been estimated to be less than 10-4 for the deposited silicon oxycarbide films in the visible and near-infrared wavelength regions. Morphological and structural characterizations with SEM and XRD confirms the amorphous phase of the SiOC films.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
PDF
