1. Introduction
Railway infrastructure particularities, together with the high level of technical compatibility with railway vehicles, ge-nerate direct influences upon the entire operational process of the railway system. In other words, a very specialized domain is the maintenance of the structural subsystem infrastructure, command-control, signalling and energy.
Due to its complexity and technical regulation level, the conventional railway system demands special attention. The problem comprises both the continuity of maintenance works and the quality of the repair works toall the elements of the system. Such actions often demand significant investments from the budget of the railway infrastructure manager, the state budget, European funds or other financing sources.
The effects of railway infrastructure investments generally have a long-term impact. They appear under the influence of a wide range of aspects that are not imperatively related to the budget of the state authority (Ministry), infrastructure manager or railway transport operators.
A conventional railway system that presents high technical standards, together with the operation of performing railway vehicles (high traffic speeds, low energy consumption, high comfort, high reliabi-lity, heavy load capacity etc.), has positive effects, especially on human activities. The most important of them are:
• increasing population mobility
• decongesting the road transport network and implicitly reducing the number of road accident casualities. Thus, an effective combination of the advantages specific toeach transport mode is obtained, for the railway system (much higher energy efficiency, lower impact on the environment, the possibility to significantly increase travel speeds, a high level of independence of climate conditions, lower noise, higher freight volumes, an incomparably greater safety etc.) and for the road system (flexibility, high availability, the modularity of the bidded capacity, the possibility of providing a “door to door” transport etc);
• reducing the environmental impact of transport (emissions of polluting substances, gases and noise);
• high level of safety for passengers and freight.
The railway system provides a safety in operation approximately 2000 times higher than road transport. For each victim of accidents caused exclusively on railway there are over 2000 victims of road accidents. In this context, the accidents and incidents caused exclusively by the railway transport system are: collisions between trains, derailments, breakdowns of railway infrastructure elements, fires etc. Accidents caused by external factors are not included (force majeure events, robbery etc.);
• the relatively reduced space for railway infrastructure operation in comparison with road infrastructure;
• providing efficient connections between human settlements, especially in terms of labour dynamics;
• advantages related to the possibilities of locating and concentrating industrial centres (regardless of their dimensions) outside the heavily populated areas.
In heavily industrialized states, the correct awareness of these aspects by the responsible decision-makers has generated the elaboration and implementation of efficient policies/strategies on railway transport. Experience has shown the emergence of social and economic effects for this category of states.For example: China, France, Germany, Japan, the USA and Spain.
Unfortunately, such ways of elaboration and approach of certain strategies have not been specific or approved in Central and Eastern Europe. For the Romanian State, the present economic and political context doesn’t provide a supportive framework for generating a potential vector for the wide development of the conventional railway system. The causes are multiple. Moreover, the Romanian railway infrastructure is confronting with a diminution of the financing process, indispensable for the running repair and maintenance of high traffic speeds that correspond to the conditions and geographic characteristics of this territory – 120 km/h for the majority of main lines and 160 km/h for recently rehabilitated European corridors.
The present article aims to point out the main dependencies between the level of infrastructure investments and their long-term effects (investment effects). The approach is not elaborated for a particular railway infrastructure manager. References and exemplifications of concrete situations are used.
The differences between maintenance, repairs and investment activities are vehement. The first category ensures the maintenance of the technical characteristics of the system above a minimum level imposed under specific regulations. The investments consist in allocating financial resources to the railway system, as a result of transport policies and strategies. Their purpose is to significantly improve at least one of the essential requirements of the railway system .
The railway service quality is closely related to managing specific problems related to technical and commercial aspects, such as: maximum traffic speed, commercial speed, traffic intensity, transport capacity, maximum admitted tonnage, maximum train length, maximum axle load, the environmental impact, noise pollution, railway safety etc. Some of them represent the ensemble of the so-called “traffic conditions” that influence the movement of railway vehicles on the network.
Railway infrastructure modernization process, as structural substitute, determines the increase of the traffic speed and the maximum admitted tonnage. This has positive effects on traffic intensity and commercial speed.
An investment that generates the growth of the maximum axle load determines modifications of the transport capacity and of the maximum admitted tonnage for that line (millions of gross tonnes transported).
2. Degradation of the conventional railway system
In time, the chemical and physical phenomena to which the railway infrastructure materials are exposed lead to the modification of certain characteristics. The modifications can be permanent or temporary, caused by prolonged exposure to certain conditions or abnormal operating factors. We refer to the cases in which the design stress limits are exceeded. The transformations suffered by the infrastructure elements depend firstly of the initial quality of construction and repair works.
The direct interaction with railway vehicles represents the main cause of the wear-out process. The environmental conditions are also affecting in time the behaviour of materials.
Most of the railway infrastructure elements have a nominal life-cycle, at the end of which they must be replaced through the modernization or renewal programmes. The wear-out and degradation phenomena, together with the replacement after the end of the life-cycle, represent a cyclic process, well-defined by the technical standards and related regulations. The conception and design phase has as main objective to establish, if possible, identical or similar periods (cycles) of use for most of these constituent elements. Thus, a larger category of materials are subject to maintenance or replacement processes, which facilitates the entire technological effort of railway line maintenance. Thus, operation restrictions or limitations are prevented.
Unstable repair or replacement cycles generate unfavourable situations that sometimes impose speed or tonnage restrictions/limitations. In extreme cases, it is necessary to interrupt the traffic until the remediation of the situation. Such situations are caused by the decrease of the basic parameters, designed below the minimum admitted limit, in which case the requested safety level can no longer be guaranteed.
The ensemble of the characteristics of the constituent elements represents the technical condition of the line. Figure 1 schematically presents the phenomenon of railway line degradation – the cycle between two repairs.
The technical condition of the line suffers modifications over time, after a decreasing variation. In order to facilitate the understanding of the phenomenon, the variation is represented linearly. In reality, however, the decrease in time of the technical condition can present different forms (concave, convex, variable, criss-cross etc.), depending on a series of factors, such as stress level, variations of environmental factors, accidental stress (figure 2, case III) etc. The approximate forms of the railway line degradation over time are presented in figure 2.
REMARK: As a result of the significant real differences between the parameters presented on the abscissa and ordinate, the figures are presented anamorphically.
The notes in figure 1 and 2 have the following meaning:
Technical condition of the line – a synthetic measure resulted through the integration of the characteristics and condition of all considered constituent elements. Generally, when we refer to the technical condition of the line, we also refer to the maximum traffic speed, maximum admitted gross tonnage or maximum admitted axle load;
Degradation process – the phenomenon of decrease of the level of parameters of the constituent elements caused by the normal and/or accidental stress, environmental conditions or the appropriate observance of designed exploitation parameters;
• T0 the initial moment or the moment of putting into operation/replacement/repair of the constituent element or of the railway line;
• S0 the technical condition of the line corresponding to the moment T0 as maximum value;
• Sf the minimum value of the technical condition of the line, corresponding to the end of the lifecycle (Tf );
• Tf the final moment of the lifecycle, when the technical condition of the line reaches the minimum value (Sf);
• Pt the lifecycle of the line or of the element, during which the technical condition reaches the maximum ( S0), or the minimum initial value (Sf). Pt can have a wide range of vaues During this period, repairs and replacement works of rail subassemblies are necessary. The process is valid for most of the specific railway infrastructure subassemblies.
Figure 1 shows that at a certain intermediate moment Ti, situated in the interval [T0 – Tf ], the technical condition of the line has a specific Si value. This aspect has a high importance in the analysis of infrastructure behaviour after a specific period Pi compared with To . In most cases, the stress of the railway lines suffers modifications as a result of the changes occurred in the industrial activity, the emergence of new tendencies in freight transport, the development of some geographic areas etc. All these factors have a certain influence upon the degradation process (figure 2 – cases I, II and III), including the operation period between two repair works (Pt ).
3. Influence of stress on railway infrastructure quality
The experience of the exploitation of railway lines has demonstrated the fact that in the majority of cases, there is interdependency between the technical condition of the line and the other characteristics related to its quality. Figure 3 offers a schematic presentation of the relations that can appear between the technical condition of the line, maximum tonnage, maximum speed and the sound level for a certain section.
A decrease of the line quality between the limit values S0 and Sf can also determine a decrease of the maximum tonnage, from the value tmax , corresponding to the initial moment To , to a value inferior tmin . Thus the necessity of introducing tonnage restrictions occurs in order to protect the running track. In some cases, the restrictions can be introduced until the general quality of the line reaches the value Tf . Such a situation is unfavourable especially in terms of affecting the transport capacity of the respective railway line. Running track degradation often implies speed restrictions or limitations. The initial maximum value Vi reaches a minimum Vf.
Another important argument is the noise level, more precisely, the noise generated by train traffic. The better the quality of the rail contact and the track geometry are, the lower the noise level. The defects of the track surface, together with vertical geometric defects of the rail-sleeper assembly and the imperfections of the running profile of the wheels generate noise pollution with negative effects. The noise level increases starting with the initial moment from a minimum value Nsi , to a Nsf maximum .
The permanent maintenance of a high-level technical condition through investments in preventive maintenance has positive effects on a wide range of aspects and generates savings. Through initial or preventive investments in railway infrastructure, major railway managers (for example: DB – Germany, SNCF – France, NRJ – Japan) register medium and long-term savings as a result of eliminating the possibilities of occurrence of deficiencies with indirect financial implications.
3.1 The influence of carried gross tonnage
A railway line is characterized through a certain maximum value of the carried gross tonnage. Railway infrastructure stress refers to the maximum axle load and maximum gross tonnage of the trains travelling on the line. Manufacturers and suppliers of structural subsystems and infrastructure constituent elements are setting these characteristics at nominal values, resulted from calculations or thorough technical studies. Thus, we avoid exceeding the resistance and supporting strength of the running track or structure .
A high level of running track stress can occur due to high vertical loading (the loading level of the wagons) or due to the exaggerated length of trains, which exceeds the designed limit. Thus, the maximum axle load can be exceeded or transversal efforts that exceed the design levels can appear in the track, negatively affecting the structure of the running track.
Considering long trains, their length determines overloading due to the transformation of higher longitudinal forces in transversal loading efforts. This phenomenon takes place especially in the case of freight train winding over points in diverging position or during shunting operations. At the same time, the curves with small radius are stressed by high centripetal forces. Figures 4 and 5 present the transversal and longitudinal forces which occur when a long and a short train run over points in diverging position.
Marian CIOFALCĂ – Head of Service, Romanian Railway Safety Authority – ASFR ]
Share on:
