The goal in integrating different maintenance planning strategies is to understand the interfaces and relationships of the models with respect to the maintenance actions to be performed and to identify the optimal strategy with the highest availability of the overall system. First, a life cycle must be defined for the entire system. As in the previous assignment the total lifetime of a 1000m long tunnel is 120 years. A tram track has to be renewed after 60 years, as well as a 160m long bicycle underpass.
After combing all lifetimes for all products, we assume the same starting data and the same lifetime. We chose a lifetime of 60 years because this period match for two systems and because we focused on the availability of the local transport network and that’s why the focus is on the tram track. First of all, ranges and durations for the interventions were researched. You can see this in the following table:
Table 1 Range and Duration for the Interventions
On this basis, different scenarios for the combined overall system could be designed. We decided on four different Local Transport Networks, which are presented in the following. The first system is a 10km long track, which is underpassed by a tunnel and a track. In the second system, instead of two separate tunnels, one large tunnel was chosen for motor vehicle traffic and bicycle traffic. This makes it possible to dispense with the maintenance measures for the bicycle underpass. Since, however, with 46 interruptions in 60 years, significantly higher values are achieved for the large tunnel, the system structure in the following two options was again implemented analogously to the first scenario. In addition, scenario three combines measures between the two tunnels. For example, the maintenance measures for Bicycle and Tunnel, which recur every 10 years, were combined. Due to the logistical advantage, it is assumed that this has a positive effect on the duration. In the last scenario, the materials with the lowest maintenance requirements were selected. For sleepers, for example, this would be plastic sleepers.
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Figure 1 Scenario 1 Tram Track with two underpasses – Tunnel (Source)
Table 2 Input Variables and Results of four Design Options
The table shows both the selected maintenance strategies with a precise representation of the values, as well as the results for the different design options. Design option 4 performs best. However, all systems have very good values with over 99.8% regarding the availability of the traffic infrastructure. However, the first major interruption for new construction of tram track and bicycle underpass would follow exactly after this period. This study shows that it is possible to compare different concrete design options in this way. However, this method is very time consuming and cumbersome. Much more effective is the subsequent automation of scenario development.
For this automation, random values are chosen from the range of maintenance measurements defined in Table 2 and the corresponding maintenance strategy is generated. The number of chosen values is variable over n.grid. However, with higher values for n.grid the spectrum of selected options increases and thus also the probability to select the optimal option.
Results
Image 4 Best Design Options
Image 4 shows the best design options from the generated scenarios. Accordingly, there are minimum interruptions of 152 days with maximum intervals between interventions of 4 years. For calculation, the focus was placed on a selection of relevant, time-intensive measures in order to be able to compare the values. It is striking that some values are unchanged, i.e. clearly lead to the best result. Differences only occur for RPS (Replacement Sleeper), RPR (Replacement Rail) and RS (Resurfacing).
This can also be shown very well by means of a Pareto Frontiers (see Image 5 & 6). For n.grid 4 and 5 was chosen as value. As already mentioned, with a higher value more scenarios are created. However, the calculation of the function also takes significantly longer. On the y-axis the distances between the interventions and on the y-axis the total time of expected interruptions are shown. The resulting scenarios are grouped depending on the selected preference. We set the preference to the minimum values for the duration of the interruptions and the intervals of the maintenance measures to the maximum values. In a few cases we even get dist.inter of 7 years and still very low interruptions of just 75 days. However, it would have to be checked whether these are not random outliers or errors. Otherwise, measures should be taken every 1-3 years, resulting in about 110 days of interruption.
Image 5 Pareto Frontier n.grid = 4
Image 6 Pareto Frontier n.grid = 5
Image 7 Preference low duration and high distance of interventions
It has been found that it is easy to bundle the measurements of the tunnels because they are similar. The tram body has to be maintained separately, especially because of the spatial separation.Surprisingly, combining them would not reduce maintenance. The reason could be the higher maintenance effort of the tunnel. Independently of this, however, it is also more dangerous to guide cyclists and motor vehicle traffic together through a tunnel. Option 2 would therefore be more likely to be eliminated. For the surface of the bicycle underpass, it makes sense to paint it after the renewal and not in the 4 years before the renewal.
References
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