Mountainous roads often have to overcome considerable differences in height, which is why hairpin bends find a valid and common use. Despite this, there is a lack of specific international standards. ...Given the absence of a national standard governing the mountain roads’ design, in Italy, as in many other countries, the Swiss standard SNV 640198a is generally applied. This standard does not guarantee the correct geometric design of hairpin bends for Italian vehicle fleets and fleets according to the Directive 2002/7/EC. In this paper, the authors have developed a new methodology based on the Swiss standard upgrade, which is applicable internationally. Starting from hairpin bends’ geometric layouts provided by SNV 640198a and from related considerations, respectively, to the gyration formulae use and to swept path analysis’ simulations, they developed new planimetric layouts compatible with the vehicle fleet and with the cross-sectional dimensions of Italian roads. In this way, a generally valid methodology applicable to any international context was defined. In particular, the study allowed the definition of new geometric layouts to be used in hairpin bend design/retrofitting when it is necessary to guarantee the simultaneous entry into the bend of a 12 m long bus, and a car travelling in the opposite direction. Finally, the proposed methodology was applied to a mountain road case study in the Lucanian Dolomites area; an area of great tourist, cultural and environmental interest in southern Italy.
The paper proposes the use of the Bloss curve (also known as biparametric or bi-hyperclothoid) as a braking curve in the exit lanes of road intersections. The main international standards continue ...using the clohoid as the principal transitional geometric element, even though the limits of its use in driving regimes with non-uniform speeds are known. The proposal to use the Bloss curve is aimed at overcoming these limitations and opening a debate on the possible need to codify, even in the international standards, the use of more suitable alternative braking curves. In this context, a kinematic study was conducted by comparing the main parameters of the motion (lateral jerk, lateral acceleration, steering speed) between the Bloss curve and more traditional curves, such as clothoid and Generalized Cornu Spirals (GCS). Nine case studies were conducted, each case was characterized considering the type of transition curve used (clothoid, GCS and Bloss curve) and radius R of the exit curve (R = 60 m, 80 m, 100 m). The numerical values assumed by the kinematic variables along the transition curves were “locally” calculated, i.e. “pointby- point”, to take into account the non-uniform motion regime. The results obtained, limited to the cases studied, show that the Bloss curve better meets the kinematic conditions of the vehicle motion in non-uniform driving regimes. Therefore, the Bloss curve can be considered as a braking curve in the design of road intersections and be a candidate for further investigation to assess any additional benefits in terms of comfort, driving safety and visual perception of the geometric element.
The design of rigid pavements is historically based on the classical Theory of proposed by Westergaard in 1929, which considers the rigid pavement as a thin plate resting on an elastic ground with a ...Winkler reaction, imposing the congruence of vertical displacements at the points of contact between the pavement structure and the ground. Westergaard’s Theory provides expressions for the calculation of maximum stress in concrete slabs for interior, edge and corner load conditions. This work focuses on the development of a Finite Element model, implemented in the ANSYS® environment and calibrated on the basis of the results of the in-scale experimental model developed by Lall and Lees in 1983. The implementation of the FE model was performed through a set of steps capable of reproducing physical and mechanical conditions of the true model, which was further intended to be used for numerical analysis. After the FE model was developed, it was possible to carry out multiple simulations pursuing three main aims: to evaluate the effect of the variation of material properties on the slab stress state, to compare the maximum stresses for the interior and edge load conditions considering Westergaard’s Theory, the experimental data and the results of the numerical model, and to use the developed and calibrated model to formulate an alternative mathematical expression, which would allow calculating the stress in corner load conditions.
The growing environmental sensitivity and the reduction of natural resources create, in Italy and other developed countries, an increasing interest in the search for alternative materials to be used ...in road construction works. In recent years, the problems related to environmental sustainability have made it increasingly difficult to remove natural aggregates from quarries and, at the same time, the regulations for the management of waste dumps are more and more restrictive. For this reason, the use of recycled aggregates is experiencing a continuous increase in the civil construction sector. This paper deals with the study of construction and demolition waste (CDW) in the field of road construction, in particular for the construction of embankment, road subgrades, foundation layers and unbound bases for flexible superstructures. Three different particle size fractions were used to prepare the mixtures: the first having a coarse size and designation 0–63 mm, the second intermediate size with aggregates of 0–31.5 mm grain size and the third with the finest aggregates having a grain size of 0–4 mm. The study was carried out by analyzing three granulometric fractions, verifying the best application for each of them. Subsequently, the mix-design was investigated, operating in compliance with the requirements imposed by UNI 11531-1, EN ISO 14688, EN 13242 and EN 13285. For the unbound layers of subgrade, foundation and base, which require greater resistance to fragmentation, the use of CDW alone has shown some limitations. Therefore, in the experimentation, it was decided to mix the CDW with a granulated slag coming from the steel production in the electric arc furnaces (EAF) and with an additional CDW (0–31.5 mm) coming from the recovery of concrete with slag. EAF granulated slag was used in small quantities, due to its relatively high cost. Four eco-friendly and recycled mixtures were studied, with low economic impact and high environmental sustainability, suitable for the construction of unbound layers of road superstructures.
The paper focuses on the use of non-conventional roundabouts, such as turbo-roundabouts and flower-roundabouts, for the reduction of both functional and safety critical issues. The aim is to evaluate ...the effectiveness of non-conventional design schemes compared to conventional solutions through the implementation of vehicular traffic microsimulation techniques and swept path analysis. The work proposes two case studies in suburban areas characterized by the presence of road intersections affected by high traffic criticality. The study compares the performance in terms of average speed, queues length, time loss, vehicle manoeuvring size, etc., between the actual state and two design solutions, respectively conventional and non-conventional. The results obtained highlight the effectiveness of the non-conventional schemes adopted for both the improvement of traffic and safety parameters and for the containment of polluting emissions into the atmosphere. The work also proposes a methodological approach that can be pursued by the road designer, for the choice between alternative design solutions of conventional and non-conventional roundabout intersections.
The recycling of road and airport asphalt pavements requires greater reliability of mix design in order to ensure proper rehabilitation and effective reuse of recycled asphalt concrete. Currently, ...internationally, the most effective mix design procedures for recycled asphalt concrete with RAP (Reclaimed Asphalt Pavement) refer to guidelines developed by SuPerPave® Mixtures Expert Task Group. In this paper, according to the requirements of the European standard EN 13108, the authors investigated the reliability of the above mix design procedure. In particular, the SuPerPave® mix design guidelines were applied for dosing components of wearing course layer recycled asphalt mixture and for the determination of PG (Performance Grade) and critical temperatures of binder contained in RAP (RAP binder) and of binder added ex-novo (virgin binder). The experimental research program started from RAM (Reclaimed Aggregate Material) grading characterization and RAP binder content determination. Afterwards, rheological characterization of the RAP binder and selected virgin binder was carried out using the DSR (Dynamic Shear Rheometer) and BBR (Bending Beam Rheometer) devices. This step allowed us to identify the right virgin binder percentages to be added to RAP binder. Then, in compliance with European standards, the mix design study of recycled mixtures was carried out, identifying the necessary granulometric integrations and the virgin-binder-appropriate percentages to be added. In this phase, three different RAP percentages were used: 30%, 40%, and 50%. Finally, the experimental plan was completed with a preliminary mechanical characterization of the studied recycled asphalt mixtures. The results showed that the implemented rational mix design guarantees performance levels of wearing course layer recycled mixtures that are fully in compliance with European standards.
The paper introduces some findings about a sensitivity analysis conducted on every geometrical and mechanical parameters which characterize the use of a railway superstructure at the high velocity. ...This analysis was carried out by implementing a forecast model that is derived from the simplified Gazetas and Dobry one. This model turns out to be particularly appropriate in the explication of problems connected to high velocity, since it evaluates both inertial and viscous effects activated by the moving load speed. The model implementation requires the transfer function determination that represents the action occurred by the bed surfaces on the railway and it therefore contains information concerning the geometrical and the mechanical characteristics of the embankment, of the ballast and of the sub-ballast. The transfer function H has been evaluated with the finite elements method and particularly, by resorting the ANSYS code with a harmonic structural analysis in the frequencies field. The authors, from the critic examination of the system＇s dynamics response in its entirety, glean a series of observations both of a general and a specific character, finally attaining a propose of a design modification of the standard railway superstructure at the high velocity of train operation adopted today especially in Italy.
Building on ideas of R. Mizner, 17 - 18, and C. Laurent-Thiébaut, 14, we
study the CR geometry of real orientable hypersurfaces of a Sasakian manifold. These are shown to be CR manifolds of CR ...codimension two and to possess a
canonical connection D (parallelizing the maximally complex distribution)
similar to the Tanaka-Webster connection (cf. 21) in pseudohermitian geometry.
Examples arise as circle subbundles S^1 \to N \stackrel{\pi}{\rightarrow} M ,
of the Hopf fibration, over a real hypersurface M in the complex projective
space. Exploiting the relationship between the second fundamental forms of the
immersions N → S2n+1 and M → CPn and a horizontal lifting
technique we prove a CR extension theorem for CR functions on N.
Under suitable assumptions \mathrm{Ric}_D(Z,\overline{Z})+2g(Z,(I-a)\overline{Z})\geq 0 ,
Z \in T_{1,0}(N) , where a is the Weingarten operator of the immersion
N → S2n+1 on the Ricci curvature RicD of D,
we show that the first Kohn-Rossi cohomology group of M vanishes.
We show that whenever \mathrm{Ric}_D(Z,\overline{W})-2g(Z,\overline{W})=(\mu \circ \pi)g(Z,\overline{W}) for some
\mu \in C^\infty (M) , M is a pseudo-Einstein manifold.
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