SAMCO Final Report 2006 F09 Report on Bridge Management
2. The growth is represented by a move from a damage rating to another. This growth is modeled by Markov-chains, which essentially uses a prediction of the probability for moving to a certain other damage rating over the next pe- riod. This next period is usually 5, 10 or 20-25 years.
The repair options are considered by the bridge manager, by estimating the repair costs, the service life of the repair and evaluating which repairs, that are possible at a given damage rating.
The strategies possible for the individual bridge are compared and the NPV (Net Present Value) estimated for each strategy. The NPV would usually include the indi- rect traffic delay costs for the users of the bridge (drivers, passengers etc.).
It must here be pointed out that major traffic delays leads to quite direct costs for the private operators, since they will immediately lose costumers and income, just as their approved rates may not be increased as otherwise expected. The public funded operators will usually be able to argue for an increased funding in case of major traf- fic delays, due to the political pressure.
The optimal strategy would usually be considered to be the cheapest (lowest NPV) and would often lead to the conclusion that the repairs should be postponed for an- other 5-10 years.
The priorities for choosing the bridges to repair are that the bridges with safety prob- lems will receive the highest priority and the rest will be based on the NPV- estimations and the availability of funding. Safety problems can be for the structure or for the users, e.g. due to cover falling off and falling down on the highway.
The private operators of highways (toll-roads) have the option of actually postponing the repairs until the optimal point (from a financial point), since they can invest the money in e.g. bonds, new facilities or take a loan for financing the repairs.
The government-funded operators (national road directorates) are not allowed to take up loans and can not place the money anywhere, but are obliged to either spend the money in the fiscal year or accept a reduced funding. These operators will therefore be forced to carry out a more constant amount of repair activities in order to avoid a major backlog of repairs in e.g. 10 years time.
The biggest uncertainties for the bridge management are in the assessment of the structures condition and in the damage growth and the consequences on this growth. These uncertainties can be reduced to a large extent by monitoring and NDT- inspections combined.
The lack of standardization in the following items:
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