1,721,172 research outputs found
Hgv collisions with steel road safety barriers: combined influence of position of center of mass and tire pavement friction
No full textAbstract
Vehicles colliding with highway safety features do not always produce the same effects. Each impacting vehicle will have a different outcome, depending greatly not only on its mass, velocity and impact angle, but also on the position of its center of mass and on the tire-pavement friction. This study analyzes in what way barrier and impacting vehicle behavior is affected by changes in the position of the center of mass and in the tire-pavement side friction, in order to identify the most dangerous loading systems. Towards this aim numerous simulations of a collision of a truck against a steel road safety barrier were carried out through non-linear dynamic finite element analysis. The results obtained demonstrate that the position of the center of mass is of greater consequence in collisions where impact energy is close to maximum barrier containment capacity and in friction-favoring conditions. The center of mass longitudinal position has a large impact on the risk of the vehicle passing over the barrier or rolling over. If it is in the back, the most common loading system, the risk of passing over the barrier is rather limited compared to rollover risk. As the position of the center of mass is pushed forward, on one hand rollover risk is reduced but, on the other hand, the risk of passing over the barrier increases. If the height of the center of mass increases, rollover risk is higher, but without significantly influencing displacement and the risk of passing over the barrier
Studio sulla severità dell'urto contro le barriere stradali di sicurezza in relazione alle condizioni d'impatto
No full textVehicle Occupant Impact Severity in Relation to Real World Impact Condition
No full textLongitudinal safety barriers are tested in order to assess the safety barriers containment capacity and the vehicle occupant impact severity. In the EN standards, the occupant impact severity is evaluated with the same test (TB11) for all the classes of barrier: a 900 kg car colliding with impact speed equal to 100 Km/h and impact angle equal to 20°. Considering that real world impact conditions may be substantially different, at least two questions arise:
1. Which is the distribution of passenger cars kinetic impact energy for different type of roads and which is the relative position of the conventional test?
2. Are the values of Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV) and Post-impact Head Deceleration (PHD) obtained in the conventional test TB11 representative for real world impact conditions?
The “correct” answer to these questions requires a very expensive research program. This because a huge number of accident reports has to be collected and each accident events has to be reconstructed, furthermore many computer crash simulations have to be performed. In order to get a “preliminary” problem assessment, a study has been carried out performing an accident analysis and many crash simulation in different impacting conditions.
The accident analysis has been carried out by the examination of 160 police run off the road accident reports on a rural dual carriageway road, integrated with the inspection of accident sites. Many accident parameters have been evaluated and distribution probabilities of impact velocity, impact angle and vehicle mass have been drawn. The real world impact conditions obtained have been used as input for the crash simulation of a passenger car against a longitudinal safety barrier. Impact simulations have been carried out by non-linear dynamic finite element analysis performed with the software LS-Dyna. The finite element model used for the vehicle is the result of an extensive modeling activity and is very capable to represent the crash dynamics and consequences.
Collision outcomes in terms of THIV, PHD and ASI have been evaluated for each impact condition and, by combining the impact condition distributions with these results, the distributions of the impact severity indices have been assessed. The study carried out show that the probability of outcomes greater than the ones of the TB 11 are equal to 26% for ASI, and 34% for THIV and PHD.
According to the results of the study, passenger cars crash test conditions more representative of real world impacts, on motorways and on rural dual carriageway roads, would be:
Impact speed = 130 km/h;
Impact angle = 20 degrees;
Vehicle mass = 1500 kg.
Such impact conditions would represent the ninetieth percentile of cars kinetic transversal impact energy. Moreover, with reference to the rigid wall fixed to the ground used in the simulations, they give rise to ASI, THIV and PHD values more severe than eighty-five percent of real world run off the road accidents.
The previous results show that the conditions proposed by the standard could be not conservative in Italy. They have to be intended, however, as preliminaries and stressing the need of a more in depth research program
In-depth Investigation of Run-off-the-Road Crashes on the Motorway Naples-Candela
No full textIn the paper, results from in-depth investigation of 1,092 run off the road (ROR) crashes on
the motorway A16 (Italy) are presented. The research is aimed at pointing out risk factors that
can address highway agencies and designers toward the selection of safety countermeasures
aimed at reducing ROR crashes frequency and severity. Crash data were collected trough the
analysis of police crash reports and relate to the period 2001-2005. Basing on police and
hospital reports, each crash was categorized in six injury levels. To determine whether a
specific crash pattern of the analysis group was significantly different from that of the control
group, the Chi Squared (χ2) test with Yates’ correction was performed.
Severity of motorcycle crashes was significantly higher than severity of other vehicle
types. In adverse environmental conditions (night time and wet pavement), crash severity was
lower than in favourable conditions. Crashes against ditches, walls, foreslopes, and
backslopes were more severe than crashes against roadside steel safety barriers. Comparison
between severity of crashes against longitudinal safety barriers and their blunt end terminals
showed a dramatic increase in crash severity against the terminals. Thrie-beam roadside
barriers that meet EN 1317 performance criteria showed a smaller crash severity and a better
performance compared to older W-beam roadside barriers. Median New Jersey concrete
barriers, compared to median steel safety barriers, showed greater crash severity and greater
proportion of rollovers, not counterbalanced by a significant better behaviour in relation to
penetration and override.run-off-the-road crashes, injury levels, concrete New Jersey safety barriers, steel
safety barriers, blunt end terminal
Il controllo di gestione e la misurazione delle performance aziendali pubbliche
No full textIl contributo del lavoro è individuabile nell'applicazione dei generali principi dei sistemi di controllo aziendale nell'ambito della pubblica amministrazione, in particolare dei musei a conduzione pubblica. L'analisi prevede l'individuazione delle variabili interne (economico-reddituali; organizzative) ed esterne (di mercato; di utente) che, messe a sistema dal sistema di controllo, possono essere monitorate dando così le informazioni volte a migliorare l'evoluzione delle performance della gestione
Parte 4: Criteri di Impiego delle Barriere di Sicurezza in Presenza di Cantieri Stradali
No full text
HGV Collisions Against Road Safety Barriers in Relation to the Parameters which Define Impact Severity
No full textWorldwide, the road safety barriers containment capacity is evaluated by full scale crash tests which are performed according to specific crash conditions. In the most common benefit-cost analysis aimed at evaluating roadside safety alternatives and in the most common road safety barriers selection procedures, the barrier’s performance limit is assumed as the maximum Impact Severity of the crash tests successfully performed, that is the vehicle’s kinetic energy evaluated by the lateral component of velocity. In this paper the effectiveness of IS has been assessed. At this aim a great number of collisions of an Heavy Goods Vehicle against a steel road safety barrier were simulated through a non-linear dynamic finite element analysis, each one characterized by the same value of kinetic transverse energy and different values of the parameters that define IS: vehicle’s speed, mass and impact angle. The results obtained show that the collision outcomes noticeably change with these parameters: the smaller the impact angle and mass the greater the barrier’s displacements and vehicle’s rollover risk. Due to this influence the Limit Impact Severity of safety barriers considerably changes with the impact conditions. To address this problem, at least for the barrier and the vehicle considered in the study, an analysis aimed at evaluating the relationships between Limit Impact Severity and vehicle’s impact angle and mass has been carried out. The expressions obtained allow to evaluate the vehicle’s containment taking into account both the IS value and the values of vehicle’s mass and impact angle
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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