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.
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.
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.
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.
“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.
When you say about a thing or a being that they are robust, you imagine a complete entity from the point of view of its component parts giving out force and safety. The notion of robustness is associated with a lot of activity domains. Consequently, there are many definitions individualizing the robustness notion depending on the study domain.
The work aims to join in the present day studies with a new research in the bridge domain. The object of the study is represented by three low track steel lattice girder railway bridges.
In the article there is also presented the way the structural robustness notion is to be found in the national codes.
A discussion of the dominant factors affecting the behaviour of long span cable supported bridges is the subject of this paper. The main issue is the evolution of properties and response of the bridge with the size of the structure, represented by the critical parameter of span length, showing how this affects the conceptual design. After a review of the present state of the art, perspectives for future developments are discussed.
This paper examines the need for a Public Procurement Maturity Model (PPMM) in organizations with the role of road infrastructure buyers under public procurement legislation in a monopsony market structure. The environment used to contextualize the information is Romania and CNADNR (Compania Națională de Autostrăzi și Drumuri Naționale din România).
The literature research, open data as well as my own practical experience are used as entry data for the four parts of the paper: (i) the context leading to the PPMM need identification, (ii) an overview of the existing public (procurement) maturity models; (iii) discussions and (iv) summary, limitations, and outlook.
The paper provides arguments of an upstream intervention in the value chain of road transport infrastructure and highlights the benefits of such an intervention. Elements such as Romanian cultural dimensions, type of market structure or impact of the outcomes of public procurement process for road infrastructure are considered relevant entry data for an intervention which aims to contribute to the improvement of performance at a procurement process level.
The results of this paper serve as a starting point for further reflection on the performance in road infrastructure public procurement area in Romania. In addition to the awareness of the need for an intervention at a contracting authority level, the paper arguments that market structure or national cultural dimensions must be considered as entry data in designing maturity models.
This paper aims to establish the interface conditions influence on the flexible pavement structures life. The methodology consists in using the interface constitutive model available in the Alizé calculation program to calculate the stresses and strains in the flexible pavement structures.
The design criteria related to limiting fatigue cracking of asphalt layers and permanent deformations at the subgrade level from the road bed are used to estimate the flexible pavement structures lifetime.
When calculating the critical stresses and strains, most mechanical design methods of the flexible pavement structures considers that the road layers at interfaces are perfect bonded or total unbonded.
Proper modeling of the interface binding condition is an important aspect in understanding the real behaviour of in-service flexible pavement structures.
Very often, pavements constructed in an economical manner or matching surface elevations of adjacent lanes cannot be designed for the soil conditions of the existing subgrade. Therefore, there is a need to stabilize the soil with an appropriate chemical substance in order to increase its strength to a satisfactory level. For the enhancement of subgrade soil strength characteristics, lime and cement are the most commonly used stabilizers. An experimental program was directed to the evaluation of a clayey soil and its mixtures with different cement contents performing tests on the index properties, the moisture-density relation, the unconfined compressive strength, and linear shrinkage. There is a definite improvement in strength. The time interval used to cure the prepared specimens affected positively both strength and plasticity features of the mixtures. A comparison with mixtures of the same soil with lime has been made, because of the wide use of lime in clay soil stabilization projects.