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Flexible Pavement Design Criterion Based on Octahedral Shear Stresses

Abstract

The judicious pavement design is the key factor in achieving the longest service life and the lowest maintenance and rehabilitation costs. It is based on the consideration of the phenomena in which the pavement structures are subjected to exploitation and the limitation of their destructive effects.

The aim of this study is to verify the possibility of implementing in the flexible pavement structures design practice of another design criterion based on limiting the bituminous mixtures creep phenomenon and that to be called: The criterion of admissible octahedral shear stresses in the bituminous layers.

Estimation of octahedral shear stresses is done with a calculation model based on finite element method, and hereafter referred to as 2D ASFEM (2D Axi-Symmetric Finite Element Model). The paper presents the results obtained by modeling several specific calculation assumptions for the behaviour of flexible pavement structures in service.

The study underlines the fact that the Octahedral Shear Stresses Ratio (OSSR) can be an additional design criterion to be taken into account when designing flexible pavement structures alongside other established criteria.

Open access
Seismic Isolation of Bridges Using the Principle of Electromagnetic Attraction and Repulsion

Abstract

This paper presents a new type of seismic isolator that uses the principle of electromagnetic attraction and repulsion, to control the friction force between two electromagnets during earthquakes. The two electromagnets are used in conjunction with a secondary high friction dissipating and damping mechanism composed from a 10mm thick neoprene ring layer and two steel surfaces coated with Si3N4 that are used to dissipate the kinetic energy in the bridge deck at some maximum ground accelerations. The isolator utilizes tri-axial accelerometers embedded in the abutments, high current rechargeable batteries and an automated controlling unit. The presented isolator was developed specifically for a concrete bridge deck with a span of 36 meters and simple supported on two abutments, using time history electromagnetic and structural analyses. The paper presents the advantages of using this active seismic isolation system, compared to classical passive devices and the important results obtained in terms of decreasing internal forces on the substructure elements cross sections together with the reduction of relative displacements between the two electromagnets.

Open access
Significance of Fines in Hot Mix Asphalt Synthesis

Abstract

According to their size, aggregates are classified in coarse grained, fine grained, and fines. The determination of fines content in aggregate materials is very simple and is performed through the aggregate washing during the sieving procedure to define the gradation curve. The very fine material consists of grains having a size lower than 63 μm. The presence of fines directly influences the composition and performance of concrete and asphalt mixtures (e.g. asphalt content, elasticity, fracture). The strength and load carrying capacity of hot mix asphalt (HMA) results from the aggregate framework created through particle-particle contact and interlock. Fines or mineral filler have a role in HMA. The coarse aggregate framework is filled by the sand-sized material and finally by the mineral filler. At some point, the smallest particles lose contact becoming suspended in the binder not having the particle-particle contact that is created by the larger particles. The overall effect of mineral filler in hot mix asphalt specimens has been investigated through a series of laboratory tests. It is clear that a behaviour influenced by the adherence of fines to asphalt film has been developed. The optimum bitumen content requirement in case of stone filler is almost the same as that for fly ash. It has been found that the percentage of fly ash filler is crucial if it exceeds approximately a value of 4%.

Open access
The Time-Space Approach in the Analysis of Traffic Safety on Rural Road

Abstract

Analysis of the traffic safety factors in some region (road, section of road, road’s kilometer) is an important task in the field of traffic safety. It is necessary to constantly monitor, analyze, compare traffic safety situation in order to develop and improve measures for increasing the level of traffic safety. The first part of each analysis is finding of positions of traffic accidents and its casualties, in other words it is necessary to find its coordinates in the space-time coordinate system.

This paper shows results of the descriptive statistical analysis of traffic accidents frequency on the rural road for the period 2005-2011. It will be point out advantages and disadvantages of this approach and also it will be suggested a new individual approach for determinate the mean time between consecutive traffic accidents.

Open access
Improved Prioritization Criteria for Road Infrastructure Projects

Abstract

This report’s main aim is to propose a methodology for assessing state-budget-funded projects based on a rigorous selection model, including clear and effective prioritization criteria. This report first argues that project prioritization and selection should be optimized against four dimensions: absorption, impact, legitimacy, and capacity. Second, it provides a diagnostic of the National Program for Local Development (PNDL), managed by the Ministry of Regional Development and Public Administration (MRDPA), as the most significant source of state-budget funding for local infrastructure projects. The PNDL’s current design and implementation leaves room for improvement, as reflected by the lack of strategic direction in allocating funds and the continued rise in the number of projects that get started without a feasible timeline for their completion. Further, this report makes recommendations for improvement of project evaluation and selection procedures for local infrastructure development projects, with a special focus on prioritization criteria and viable funding sources for each type of investment. The practical purpose is to enhance the efficiency and effectiveness of proposed investments, maximizing impact in the context of inherently limited available financial resources. A complementary focus is on opportunities for harmonizing and better coordinating investments across various sources of funding, in the context of nearly EUR 40 billion available to Romania from the EU for the 2014-2020 programming period.

Open access
The Influence of The Static Layout on The Stress and Deformation State for Concrete Arched Bridges with Upper Carriageway

Abstract

Arch bridges were the first constructions with considerable spans built by man, due to the materials and technologies available at that time. Afterwards, these works of art have diversified and are now solutions used in countless situations, especially when crossing deep valleys.

Both their economic and architectonic aspects are hard to combat and have led to selecting this type of structure for more and more locations.

The paper will contain a brief presentation of some aspects regarding upper path concrete arch bridges composition and design methods. Also, it will have a case study regarding structural stresses over the different construction stages, and for several support hypotheses.

The case study will reflect the Crivadia viaduct, situated on DN 66, at km 150+672. The bridge has a main span of 59.20m and an overall height of 15.00m, serving a 7.80m wide carriageway and two 2.20m wide footways. It has a total length of 107.60m.

Based on the results of the case study, conclusions will be drawn regarding stress variation over the construction stages and under different support hypothesis, comparing these with the initial results.

Open access
Numerical Models used for The Calculation of The Cable-Stayed Bridge at Km 0+540 over Danube-Black Sea Canal

Abstract

Cable-stayed bridges are complex structures and for their design, the traditional calculation methods are hard, even impossible to use for a global analysis. Separate analyses for the each component of the bridge in a simplified manner can be conducted, but in this case the concurrence of the elements into the structure is not taken into account, leading to errors in estimating the structural response. For these structures, the construction method and the presence of the stays, which are elements having a nonlinear behaviour, implies to consider a nonlinear staged analysis including the second order effects in order to transmit form one stage to the other the stress-strain state.

In the present time, thanks to the evolution and development of the calculation methods and computer analysis, cable-stayed bridges can be accurate analysed so that the obtained response is close to the behaviour of the structure during erection and later, in service.

The aim of this paper is to present the results obtained using one of the finite element models and nonlinear staged analysis of the bridge at km 0+540 over Danube-Black Sea Canal near Agigea. Inside the paper, results related to the evolution of stress-strain state in principal structural elements of the bridge - pylons, stays and deck - during the execution and in final stage, in service are to be presented.

Open access
Research Concerning The Distribution of Temperature in Asphalt Mixtures with The Help of Thermo-Physical Characteristics for Laboratory Tests

Abstract

The characterization of the material through laboratory tests performed on asphalt mixtures offers significant performance predictions for asphalt pavements only when the material temperature is correctly taken into consideration. This paper presents an analytical pattern which, based on the thermo-physical characteristics, can predict correctly the distribution of temperatures in the mass of asphalt mixtures.

The paper also presents the organizational structure of laboratory testing, designed to validate the model for temperature determination. The temperature measurements are realized on a range of cylindrical samples at different moments in time, after submitting the sample from a low balance condition to a high balance condition by placing it in the environment precinct, according to the future test.

In conclusion, the paper aims at realizing and developing a model as a practical instrument able to offer a reliable assessment concerning the time required in order to reach the testing temperature specified for the samples of asphalt mixtures for different laboratory trials.

Open access
The Roller-Ground Dynamic Interaction in The Compaction Process Through Vibrations for Road Construction

Abstract

The natural soil used in filling the embankment of the road communications is characterized by the following factors: humidity, porosity, toughness. For certain factor values that describe the soil state is distinguished a certain soil behavior under the influence of the external forces applied through static or dynamic mechanical means.

In this study are presented the numeric simulation results of the soil-compactor interaction based on the complex and nonlinear rheological model proposed by the author in the result of the elaborated doctorate thesis, that follows the real soil characteristics (elastic, dissipative and plastic) on those of the compaction equipment (with a single vibrating roll). The model was harmonised and granted in accordance with the results obtained from the processing of the experimental data. For the simulation model was used the specialized software package Matlab (Simulink, SimMechanics). The obtained results revealed the real behavior of the equipment and its action on the compacted soil.

Open access
“Warm Mix Asphalt’’ for Airport Use

Abstract

“Warm Mix Asphalt” (WMA) is a technology developed to obtain an asphalt mixture at lower temperatures. The method has significant benefits for the economic and environmental area.

As known, “warm mix asphalt” uses additives in bitumen having the purpose to reduce the viscosity in order to decrease the mixing and compaction temperatures.

Hot mix asphalt used in the airport area, especially the area of taxiway and the apron must satisfy beside usual requirements for roads, some requirements related to fuel resistance and de-icing agents according to European norms.

Does warm mix asphalt for airport use meet the requirements according to European norms? This is the question from this paper which aims to determine the characteristics of asphalt mixtures for airports BBA16 when using or not using an additive, considering a series of laboratory tests: cyclic triaxial compression test, fatigue test, stiffness modulus test and resistances to fuels test.

Open access