An important aspect in the reassessment procedure illustrated in Figure 12.2 is that the
knowledge about the structure is established and refined in an adaptive manner according to
the actual need.
A successive assessment of an existing structure as described above may hence involve
evaluations which, in terms of refinement and detailing, span over purely heuristic experience
based statements over application of deterministic safety formats to instrumentation, testing
and probabilistic analysis.
Inspection strategy based on known deterioration
In Figure 12.3 the general adaptive approach from Figure 12.2 is adapted to the special
features of concrete structures.
To start with it is proposed to perform from the top and downwards a systematic identification
of the critical structural elements i.e. the most utilized structural elements, and the
corresponding failure modes. For each type of critical structural elements one or more
deterioration mechanisms are identified and observable damage indicators for these
deterioration mechanisms are listed. It is understood that the notion of damage indicators is
broad and includes e.g. ingress of chlorides, half-cell potential readings, malfunction of
bearings etc. The location of the critical structural elements will give guidance as to where
testing and inspections are relevant.
Taking basis in the physical understanding of the failure modes the material parameters,
which are important for the critical structural elements and for the possible future states which
may be related to significant economical consequences, are determined by sensitivity analysis.
For some failure modes it may be the yield stress and/or geometry of the reinforcement, which
is governing, and in other cases it is the concrete compressive strength, the concrete cover, the
diffusion coefficient, etc. This evaluation will serve as basis for deciding on the type of testing
on the individual critical structural elements.
The observable damage indicators are the subjects of interest for the inspections. Some of
these may be easy to inspect but bare little information regarding the deterioration state and
visa versa. Depending on the type of damage indicators there will be different possibilities for
the choice of inspection methods. The adequacy of the different inspection methods in relation
to information they provide about the underlying deterioration process shall be quantified.
However, in most cases the choice of the inspection method will be evident given the damage
indicator.
Knowing the locations of the critical structural elements and the corresponding damage
indicators gives guidance to the amount of required inspections. However, the amount of
inspections may still be restrictive if the number of critical structural elements and/or damage
indicators is large. In this case it is worthwhile to evaluate whether or not common cause
effects are underlying the deterioration states. If this can be justified by argumentation and
e.g. supported by evidence from the structure the number of inspections may be considerably
reduced as only a reduced sample of critical elements and damage indicators need to be
inspected.