Particular diligence in the preparation of documentation and conducting a tender procedure for construction works must be made by public contracting entities, who are subject to additional restrictions. In Poland, the largest public contracting entities are the sectoral ones. These are the entities (defined in Art. 3 of the Public Procurement Law Act) operating in the sectors of water management, energy, transport and postal services. The paper presents the analysis of tender offers for the execution of construction works or design and execution of construction works related to the reconstruction, construction and revitalization of railway lines, announced after the amendment to the Public Procurement Law on June 22, 2016. The considered examples are selected tender procedures covering the scope of construction and assembly works on railway lines throughout the country. The authors paid particular attention to the tender criteria applied and the requirements for the potential contractors for works in the field of railway infrastructure.
Almost every construction investment should contain elements of risk forecasting, whose validity depends, among other things, on the correct assessment of potential threats. These risks were defined by the Authors as risk factors that were characterized and then grouped on the basis of performed research in the scope of their identification. Due to lack of method of scheduling railway investments on the construction market, including risk assessment, a research effort was undertaken [14-17], the result of which is the proposed method. The article presents the main assumptions of the original method of rail investment planning, which on the one hand, will take into account the impact of potential threats identified previously by the Authors, and, on the other, will allow project managers to refer to the conditions in which the implementation of a specific facility is planned. The assumption was made that the method, relatively easy to implement, supported by an appropriate computational program, will encourage teams planning the implementation of railway undertakings to its application and will improve the reliability of the schedules they develop.
The dynamic analyses are of key importance in the cognitive process in terms of the correct operation of structures loaded with time alternating forces. The development of vehicle industry, which directly results in an increase in the speed of moving vehicles, forces the design of engineering structures that ensure their safe use. The authors of the paper verified the influence of speed and vehicle parameters such as mass, width of track of wheels and their number on the values of displacements and accelerations of selected bridge elements. The problem was treated as the case study, because the analyses were made for one bridge and the passage of three types of locomotives. The response of the structure depends on the technological solutions adopted in the bridge, its technical condition, as well as the quotient of the length of the object and vehicle. A new bridge structure was analyzed and dynamic tests were carried out for trainsets consisting of one and two locomotives. During the actual dynamic tests, the structure was loaded with a locomotive moving at a maximum speed of 160 km/h.
This work deals with the effect of austempering temperature and time on the microstructure and content of retained austenite of a selected cast steel assigned as a material used for frogs in railway crossovers. Bainitic cast steel was austempered at 400°C, 450°C and 500°C for two selected times (0.5 h, 4.0 h) to study the evolution of the microstructure and retained austenite content. The microstructure was characterized by optical microscopy, X-ray diffraction analyses (XRD), and hardness tests. Phase transformations during and after austempering were determined by dilatometric methods.
The increase in isothermal temperature causes an increase in time to start of bainitic transformation from 0.25 to 1.5 s. However, another increase in temperature to 500°C shifts the incubation time to as much as 11 s. The time after which the transformations have ended at individual temperatures is similar and equal to about 300 s (6 min.). The dilatation effects are directly related to the amount of bainite formation. Based on these we can conclude that the temperature effect in the case of cast steel is inversely proportional to the amount of bainite formed. The largest effect can be distinguished in the case of the sample austempered at 400°C and the smallest at 500°C. Summarizing the dilatometric results, we can conclude that an increase in austempering temperature causes an increase in austenite stability. In other words, the chemical composition lowers (shifts to lower temperatures) the range of bainite transformation. It is possible that at higher austempering temperatures we will receive only stable austenite without any transformation. This is indicated by the hatched area in Figure 4b. This means that the heat treatment of cast steel into bainite is limited on both sides by martensitic transformation and the range of stable austenite. The paper attempts to estimate the content of retained austenite with X-ray diffraction.
Poznań jako jedna z najsilniejszych jednostek miejskich w kraju ma znaczną strefę oddziaływania (obszar funkcjonalny). Naturalną konsekwencją takiego modelu rozwoju są poważne problemy komunikacyjne spowodowane dynamicznym rozwojem strefy podmiejskiej. Za ich rozwiązanie przyjmuje się oparcie układu komunikacji publicznej na węźle kolejowym i stworzenie na jego podstawie Poznańskiej Kolei Metropolitalnej. Jednak dla sprawnego funkcjonowania takiego systemu zachodzi potrzeba integracji z innymi systemami transportowymi za sprawą węzłów przesiadkowych. Celem artykułu jest ukazanie potencjału na stworzenie policentrycznego systemu multimodalnych węzłów przesiadkowych, opartych na istniejących kolejowych dworcach miejskich (dworcach dzielnicowych). W badaniach skupiono się na perspektywie pasażera, a główną metodę badawczą stanowi wywiad pogłębiony. Pozwoliło to uzyskać opinię oraz zidentyfikować potrzeby pasażerów korzystających z badanych obiektów. W trakcie badań skoncentrowano się także na analizie zachowań komunikacyjnych pasażerów oraz analizie sposobu funkcjonowania samych dworców miejskich. Dodatkowo pozyskano informację o przybliżonym celu podróży pasażerów, co pozwoliło wyznaczyć hipotetyczne zasięgi oddziaływania poszczególnych dworców miejskich. Wyniki badań pozwoliły na opracowanie szeregu rekomendacji mających na celu optymalizację funkcjonowania wybranych kolejowych dworców miejskich zarówno w aspekcie technicznym, jak i organizacyjno-zarządczym. Mogą one stanowić podstawę do opracowania koncepcji zrównoważonego transportu publicznego o zasięgu metropolitalnym.
Electrified railways are an example of AC single phase distribution networks. A non-negligible amount of active and nonactive power may be related to harmonics, especially for distorted highly-loaded systems. The paper considers the relevance of the harmonic power terms in order to identify distortion sources in a single-point perspective, in line with the approach of EN 50463 for the quantification of the power and energy consumption. Some single-point Harmonic Producer Indicators (HPI) based on harmonic active power direction and nonactive distortion power terms are reviewed and evaluated using pantograph voltage and current measured during several hours of runs in two European AC railways (operated at 16.7 and 50 Hz). The HPI based on active power shows to be consistent and provides detailed information of rolling stock characteristic components under variable operating conditions; those based on nonactive distortion power are global indexes and hardly can operate with complex harmonic patterns in variable operating conditions.
Problems concerning structures dynamics are being one of most important subjects in recent investigations associated with railways constructions. The need of modelling of such structures and their behaviour prediction leads to necessity of seeking new approaches, mainly due to highly increasing speeds of vehicles and traffic intensity. Comparative studies carried out on experimental data, measurements and theoretical research show that models based on multi-layered approach supported by semi-analytical approximations of solutions can give new insight into undertaken analyses. More detailed consideration of roads components and their physical properties, along with application of effective estimations allowing to avoid numerical instabilities linked with extremal dynamic variations, can be important tools in obtaining new solutions both, theoretical and engineering. This paper briefly presents a number of multilayer railway track models, with special emphasis on nonlinear track properties. Existing analytical and semi-analytical solution methods are presented with main advantages of new approaches. The theoretical double-beam system with two nonlinear layers is solved and computational examples are presented along with possibility of their transition to other multilayer structures analysis.
Ballast layer has weighty share in the lifecycle costs of railway track. The strict standards and maintenance rules of ballast grading significantly contribute to the ballast costs. One ways to the costs reduction is differential demands to ballast grading for the secondary and low loaded railway lines. Additional one is the different ballast grading over the ballast height. This study presents a full scale laboratory investigation of technical efficiency of such railway ballast under the long-term cyclic loading in comparison with the standard ballast layer. The double layer is presented with standard grading ballast upper layer and bottom sub ballast layer consists of ballast mixture. Pressure distribution under the ballast layer and permanent settlements of the layers are measured during the loading cycles. The reference measurements with standard grading ballast material are carried out. The study shows that initial settlement accumulation of the double layer railway ballast are lower to that of the standard ballast layer. However, the settlements accumulation intensity of the ballast is higher. The analysis of the pressure distribution measurements under the ballast layer and the settlements inside the ballast layer explain the causes of the different settlement accumulation.