number of years subject to given loads and exposures contain information of value in the
assessment situation.
First of all the possibility of inspecting and testing an existing structure may be used to assess
the condition of the structure, i.e. to what degree the structure has been damaged or degraded.
This information may then be accounted for in a further assessment of the structural
performance of the structure.
In an assessment situation in principle all uncertainties may be reduced through the available
information about the structure. Only in rare cases can the uncertainties be completely
removed. This is because basically all techniques for inspection and testing are associated
with uncertainties and these uncertainties must be accounted for consistently in the assessment.
Based on inspections and tests of the structure it is directly possible using probabilistic
methods to update the uncertainties associated with the variables of the design equations. This
not only will lead to new characteristic values but also lead to new partial safety factors. Here
it is important to notice that new information about a resistance variable will not only lead to a
new characteristic value and a new partial safety factor for the resistance variable but
moreover also change the appropriate safety factor for the load variables entering the design
equation.
The effect of collecting information related to resistance and load/exposure variables is thus
an updated set of design values to be applied in the design equations. Proof loading tests as
well as proof-loading by previous experienced statistical loading will have the principally
same effect.
It is in principle possible to apply more refined physical models than those applied in the
design codes, e.g. for the assessment of the shear capacity of concrete beam. This will lead to
a more realistic assessment of the capacity and consequently also to a reduction in the model
uncertainty. In an assessment such refined analysis possibilities are thus often an efficient
means of reaching improved structural capacity (reduced vulnerability and/or improved
robustness).
Practical Aspects of Reassessment
For existing structures the assessment process is closely interrelated with inspections. First of
all the inspections which are required for the assessment itself i.e. for establishing an
overview of the present condition of the structure, but also the inspections which are
necessary to control the future deteriorations of the structure and on the basis of which, future
maintenance activities may be implemented. In Annex B general considerations in regard to
the planning of experiments are outlined.
It is often useful to follow a two (or more) phase approach in the assessment process whereby
it is ensured that the information collected from the structure by means of inspection is
targeted for the purpose of the specific assessment. In Figure 12.2 a so-called adaptive
approach for the assessment process is illustrated. This approach is consistent with the
procedure presently being implemented in the new SIA code for the assessment and
maintenance planning of structures, SIA (2005).