This paper presents a maintenance strategy model of a system with a gamma deterioration process, regular inspection times, and intervention delay. Interventions are deemed necessary when the deterioration process is greater than an intervention level at inspection time. The objective is to determine the long-term mean costs of different maintenance strategies and to optimize these costs with respect to specific parameters, such as the intervention level or the inspection interval. Semi-regeneration properties at the inspection times and associated Markov renewal techniques are used in order to compute the long-term mean costs. This model is applied to the maintenance of railway tracks.

For any railway infrastructure manager, track maintenance is one of the most important tasks to perform. This mission requires a regular follow-up of geometric track quality and monitoring of intervention execution. Among other tools, TIMON, a computer application using track geometry measurements and maintenance operation data, is currently in use in France. This application illustrates the evolution of track quality indicators.We present a possible extension of this tool: a systematic analysis of the available data by applying a stochastic model for the track geometry deterioration is proposed. The use of environmental variables in order to identify the significance of their influence on track degradation is introduced.The stochastic model has two advantages: on the one hand it enables one to take into account the intrinsic variability of the degradation phenomenon and on the other, significant environmental variables are included into the model. The work presented here aims to classify sections of the high-speed railway network with respect to similar degradation behaviour. Two different graphical representations that could ease decision-making are proposed.

The reliability of railway equipment is of central interest in the choice of design and maintenance strategies. In high-speed trains, known as TGV, the assembly of mechanical parts is performed by the use of prestressed screws. In order to ensure safe operation of the railway network, the French company SNCF has undertaken a reliability-based analysis of the life cycle of screwed connections. This study aims at establishing a consistent reliability-based methodology for the assessment of equipments subjected to fatigue, corrosion, and imperfect maintenance operations, in order to improve their inspection on the basis of cost and reliability balancing. This methodology incorporates the life cycle of the equipment, including the deterioration modes, the imperfect maintenance operations and the uncertainties in geometry, loading, and material properties. The results of the study show that despite the high resistance regarding the applied load, the connection is still very sensitive to parameter variations: friction, tightening and prestressing. Although the large safety margin in fatigue design, the robustness of screwed connections should be sought when operation and maintenance conditions are considered.

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