1,721,080 research outputs found
THE EVALUATION OF THE EVOLUTION OF ROAD SURFACE FRICTION: A CASE STUDY IN NAPLES' DISTRICT
No full textRoad surface friction, such as all pavement surface characteristics, undergoes to a degradation through time. The
prediction of friction progression with time represents a key topic in pavement maintenance since it is important for
road managers to know where and when the maintenance intervention is needed in order to restore a satisfactory
friction level and, as a results, to guarantee an adequate road safety. For these reasons, it is necessary to quantify how
road friction decreases with the increase of time and in which manner it is affected by different factors involved in the
degradation phenomenon, among which heavy commercial vehicle traffic flow and spectrum play a critical role.
To this purpose, following a brief review of skid resistance degradation models available in literature, a friction deterioration model has been derived from site measurements carried out in a dual carriageway road within the Naples
area. Traffic flow and spectrum monitoring, on one hand, and friction (through British Pendulum) and macrotexture
(through Sand Patch method) measurements, on the other, have been performed for almost two years on a conventional
asphalt concrete wearing course and on an experimental high performance modified asphalt concrete mix. By making
use of the differential surface wear occurring in the transversal direction due to the variability of lateral position of
vehicular traffic, it has been possible to derive a friction deterioration model for both wearing courses within a
reasonably short period of time according to two equivalence damage criteria. Preliminary numerical analysis seems to confirm that a strong relationship exists between friction values and cumulated traffic expressed in terms of equivalent light vehicles for both the bituminous mixes if an equivalence damage criterion based on total tyre footprint area of vehicle is adopted. Furthermore, friction level provided by the highperformance mix appears to be always larger than that provided by the conventional asphalt concrete wearing course
Modelli di degrado dell'aderenza
No full textQuaderno AIPCR del Comitato Tecnico C1 "Caratteristiche Superficiali" presentato al XXIV Convegno Nazionale Stadale AIPCR, Saint Vincent, Aosta 26-29 Giugno 200
Modelli di degrado dell'aderenza
No full textQuaderno AIPCR del Comitato Tecnico C1 "Caratteristiche Superficiali" presentato al XXIV Convegno Nazionale Stadale AIPCR, Saint Vincent, Aosta 26-29 Giugno 200
PRELIMINARY THEORETICAL INVESTIGATION OF INFLUENCE OF TRACK GEOMETRICAL DEFECTS ON WHEEL-RAIL FORCES
No full textRail and track defects are one of the most important sources of dynamic loads generated by a moving train. The oscillations and vibrations decrease the ride comfort, increasing the track deterioration and noise emission. In the spectrum of the vibrations of railway vehicles, the track geometrical irregularities generate excitations at low frequencies, usually below 30Hz, that are responsible for the dynamic behavior of the vehicle. A comprehensive multi-body simulation model of a four-axle passenger rail vehicle is implemented in the multi-body simulation software (MBS) and it is used for analyzing the potentially dangerous running condition. On basis of these multi-body model simulations, the influence of the track irregularities on the vehicle-track dynamic interaction, mainly in terms of lateral (Y) and vertical (Q) wheel-rail forces, their ratio (Y/Q) and contact angle (delta), is investigated. Four kinds of the track related irregularities, according to the ORE B176 standard, are statistically determined: lateral, vertical, roll and gauge. Each one of these, is examined in two different levels of severity (low, high) by means of excitation signals in distance domain on the basis of a Power Spectral Density (PSD) function. In order to individuate the worst run condition varying the train speed within of this range: 70 - 200 km/h, the two different combinations of irregularity levels are implemented. Finally, the relations between the main dynamic parameters (Y, Q, Y/Q, d) and the track irregularities severity level are analyzed, under certain geometrical conditions. These studies are to be considered in preparation to future investigations aimed to obtain the best simplified model to describe the railway alignment defects occurrence and their evolution
Development and Experimental Validation of a Prediction Model to Assess Railway Traffic Induced Vibrations
No full textAmong environmental factors affecting railway infrastructure management that have to be taken into account at design level, vibrations play an important role. Because of dynamic interaction between vehicle and railway superstructure due to irregularities of surfaces coming to contact (wheel and rail) and to vehicle motion anomalies, a set of vibration type are generated propagating from superstructure through subgrade and surrounding soil up to ultimate receptors. Environmental Impact Assessment (EIA) procedures prescribe quantitative and qualitative evaluation of vibration annoyance in these receptors, but, to date, few models available in literature allow an effective assessment of frequency content and very few of these have been experimentally validated. In the present paper a vibration level prediction model for a railway superstructure on an embankment has been developed. This model, that has been also validated through field test, can be effectively used to study construction solutions, within railway superstructure, aimed at mitigating vibration annoyance
Evaluation of rail defects provided by high performance measuring devices
No full textWithin the management of railway infrastructures, rail defect monitoring is one of the most significant task since it affects maintenance interventions, on one hand, and safety of train operation, on the other. In recent years, several high performance measuring devices, providing a huge amount of data that have to be carefully analyzed, have been developed and employed to accomplish this aim. There is therefore the need to develop efficient and reliable procedures able to reduce them into efficient synthetic descriptors and to detect significant variations. In this paper a preliminary analysis following a large experimental measure-ment campaign carried out on the Circumvesuviana railway network operating in the Naples metropolitan ar-ea is reported. Track cant, level, gauge and twist data have been collected with a 25 cm sampling interval within a two year long period by using the Plasser device (POS/TG System), directly mounted on an conven-tional vehicle. Preliminary analysis show that by combining track alignment data with operational infor-mation, a more reliable prediction of the evolution of defects can be derived
Development and Experimental Validation of a Prediction Model to Assess Railway Traffic Induced Vibrations
No full textAmong environmental factors affecting railway infrastructure management that have to be taken into account at design level, vibrations play an important role. Because of dynamic interaction between vehicle and railway superstructure due to irregularities of surfaces coming to contact (wheel and rail) and to vehicle motion anomalies, a set of vibration type are generated propagating from superstructure through subgrade and surrounding soil up to ultimate receptors. Environmental Impact Assessment (EIA) procedures prescribe quantitative and qualitative evaluation of vibration annoyance in these receptors, but, to date, few models available in literature allow an effective assessment of frequency content and very few of these have been experimentally validated. In the present paper a vibration level prediction model for a railway superstructure on an embankment has been developed. This model, that has been also validated through field test, can be effectively used to study construction solutions, within railway superstructure, aimed at mitigating vibration annoyance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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