What is Risk Based Inspections (RBI)?
Risk Based Inspections (RBI) is defined as an integrated methodology that uses risk as a basis for prioritising and managing an in-service equipment inspection program by combining both the likelihood of failure and the consequence of failure.
For bridge maintenance and conservation management using this method, at first, it is necessary to perform a preliminary risk analysis, which consists of an initial screening process defining which structures are to be considered in more detail, determining the hazards to the various structural elements and how the elements can fail. All structures should be categorised as:
Structural elements that have adequate strength and are not deteriorating or likely to deteriorate are deemed to require only routine maintenance and will therefore be excluded from the strategy.
For their part, structures which fail the assessments will be deemed to require strengthening previously and will be therefore excluded from the reliability maintenance strategy. Structures which had been shown by the assessments to have adequate strength, but deteriorating, will be considered in more detail in the qualitative and quantitative stages of the strategy.
The quantitative assessment is aimed at defining intervention dates for the repair of the structures, incorporating the concept of time-related deterioration. The intervention dates shall be used as the basis for identifying the repair programme, particularly for the immediate future.
In the end, the risk-based strategy aims to use a combination of code-based and reliability analyses that allow to define priorities for repair with greater confidence. In addition, environmental risks can be included in these strategies to have a more complete view of the structure and to be able to make more informed decisions.
These are the risks derived from the conditions of the location of the structure (weather, seismic risks, etc.), and their inclusion in decision-making on maintenance, inspection and repair strategies is more necessary the more extreme the risks are (large temperature gradients, high seismic risks, etc.). To conduct a risk-based inspection, risk maps are a useful tool to graphically summarise the specific risks that could affect a determined structure. These maps usually correspond to the elaboration of an Ishikawa diagram, in which the possible causes
that could lead to damage to the structure under study are represented.
While some general risks could affect all bridge structures, there are also risks which are specific to each bridge, depending on its location, its use, particularities, etc.,N which must be identified by qualified specialists. Risk maps are drawn up considering the desired approach to risk analysis. They can be drawn up from a general overview to more specific ones, focusing on the structural
analysis of the whole structure or of a particular element or area of the bridge that may be subject to damage.
The following is an example of a risk map, from which risk-based inspections could be planned, as well as other analyses that need to be conducted, considering the hazards of each bridge. It should be noted that this is a reference list (non-exhaustive), which should be adapted to each situation by a specialist in the field.
