A management system supports the repair planning
Keeping an overview
The value of the constructions of the German Federal Waterways and Shipping Administration (WSV) is estimated at EUR 40 billion (source: http://www.wsv.de). In order for nobody to get hurt on or around these constructions and to guarantee their functionality, the WSV carries out structural inspections on a regular basis. In this context, the constructions are inspected for damage. Eventual damage is determined, evaluated and stored in the central database, WSVPruf. Depending on the severity of the damage, repair is carried out immediately, in the medium-term, or it is decided that no repair work is required.
Due to the WSV's tight budget and reduced staff numbers, the extent of the repair measures that can be carried out is limited. Therefore, it is important that any necessary repair measures are detected at an early stage, and are evaluated and prioritized so as to be able to take advantage of long-term planning horizons. For supporting this important task, the Federal Waterways Engineering and Research Institute (BAW) is developing a maintenance management system, EMS-WSV.
Grades enable comparisons
The EMS-WSV starts with the compilation of a current knowledge base regarding the state of the constructions. For that purpose, WSV specialists who are specifically trained for such inspections assess the damage found at or on a construction, describe the damage using standardized terminology, and grade each damage using a damage category ranging between 1 and 4, 4 being the highest damage category. A damage category of 4 requires immediate action. Any damage is described objectively such as to enable a comparative analysis with respect to all the constructions of the WSV. For that purpose, the WSV together with the German Federal Ministry of Transport, Building and Urban Development (BMVBS) and the BAW have taken various measures to improve, standardize and simplify the inspection of constructions. Examples are the updating/modernisation of the WSVPruf software for documenting the inspection of constructions (see BAWAktuell 03/2011), the comprehensive training of the staff members who carry out construction inspections, and the publication of the BAW Code of Practice: "Classifying Waterway Construction Damages" (see www.baw.de, MSV 2011).
In WSVPruf, in a first step, a pre-determined algorithm calculates partial grades for the damage categories of the individual damages for different trades (e.g. 'construction', 'steel structures', 'equipment'). In addition, the algorithm generates an overall grade for the entire construction, which indicates the urgency of the repair measures as characteristic numbers. In the decision-making process, with the aid of these grades, structures that require immediate action (grade close to 4) can be easily identified, as can structures that are in excellent condition (grade close to 1).
Grades provide overview
A compilation of inspection results for ten locks in Figure 1 demonstrates that locks 5 and 9 require action in almost all areas and must therefore be in a poor condition. Locks 8 and 10, on the other hand, receive good grades and do not require a closer inspection. A vertical reading of the table shows, for example, that the repair required for the equipment of locks 2, 4 and 5 can be carried out together.
Due to increasingly tight budgets and reduced staff numbers, all potentially required repair measures cannot be immediately initiated in a meaningful manner. Therefore, it becomes necessary, in a second step, to further prioritize those structures requiring repair, also taking into account factors such as the significance of the structure for navigation, available alternative routes, and the importance of the waterway. Current BAW studies indicate that this process can likewise be depicted in a structured, objective and transparent manner, using characteristic numbers.
Furthermore, it is important for the medium-term repair planning, to know how structures that have received grades 2 or 3 will evolve in the future, and when these structures will require repair.
Determining ageing functions
In principle, every object can be described by means of an ageing curve which indicates the development of the object's state over time. Due to its flexibility, the "Herz function", which was developed by Professor Raimund Herz from the TU Dresden, is especially suitable for depicting the ageing of construction infrastructure and the parts thereof. For example, steel structural elements undergo a different ageing process than the solid construction of a structure or parts of the equipment of a structure. Therefore, it is necessary to determine different ageing functions. For determining the parameters of these functions, the BAW has used the Delphi method. This method concerns a structured group discussion process which systematically compiles the expert knowledge available in the WSV and the BAW, in order to determine the characteristic values of interest. This yields ageing functions for different trades on waterways engineering structures, which describe the state of the structure in the form of a grade, from the time of building up to its failure at a later point in time. In this manner, it becomes possible to estimate the current and the future partial grade and the time of failure of the trades as a function of their age.
Projections for the future
Furthermore, a failure rate can be calculated from the ageing functions, which can be used to determine a Markov matrix. The Markov matrix, named after the Russian mathematician, Andrey Andreyevich Markov, describes the probability at which, for a specific time increment, a damage remains within the same damage category, or changes to another damage category (i.e., the damage gets worse). The method is highly suitable for projecting the state of any damages which have been determined, into the future.
By combining the two methods, it becomes possible to provide a forecast on the future development of the state of a structure. In this context, any determined damages as well as the ageing of presently undamaged trades are taken into account. The partial grades obtained from the inspection of the structure are used as the starting value for the current year. Figure 2 indicates how the partial grades for the trades 'construction', 'steel structures' and 'equipment' of a structure develop, proceeding from the starting values.
EMS-WSV supports the decision-making process
Based on the above, a technically-based threshold has to be determined in the EMS-WSV, which indicates the worst, still acceptable state. Accordingly, the intervention time i.e. the time at which repair planning should be initiated for the respective trades can be determined. For example, if the acceptable threshold state is determined to be the grade 3.5, according to Figure 2, the intervention time for the construction is the year 2033, and for the steel structures, the year 2027. Although 'steel structures' obtains a better partial grade in the beginning, it reaches the threshold at which repair is required prior to the 'construction' reaching this threshold, because the system takes into account the more rapid ageing process of the steel structural components as compared to that of the construction. The structure in Figure 2 will first require repair to the equipment parts.
Applying the above to the structures of an individual waterway, or to all the structures of the WSV, results in the overall repair requirements to be expected in the future.
EMS-WSV as an instrument for cost forecasts
In order to be able to make forecasts regarding overall cost, the EMS-WSV must also link the respective repair requirements to the expense thereof. A survey within the WSV provided data on the cost of lock repair measures carried out over the last 20 years. Taking inflation into account, these costs were initially assigned to relevant trades, and categorized as small, medium or large, according to the average cost incurred. In a further step, the repair measures and the average cost estimations thereof could be assigned to the trades of the structures, as a function of the respective damages. In this manner, it becomes possible to make a prediction with respect to the future repair cost. For ship lock plants, the above process is illustrated in Figure 3. In this context, the overall cost was extrapolated from the assessment of a subset.