These requirements, of which the latter three are understood as requirements to the structural
performance, directly or indirectly provide all required information to design a structure.
Generally, the design follows the relevant codes for the design and execution of structures
including specifications in regard to the performance of materials, testing and quality control.
If a structure is designed and constructed according to given requirements it can be assumed
that the structure is efficient and fulfils the given requirements. However, this statement is
valid only with limitations. The major limitation concerns the validity of all assumptions on
the basis of which the design was made. This includes the assumption that the extent of
degradation and damages of the structure do not exceed an intensity and extent whereby the
design assumptions in regard to load carrying capacity are no longer fulfilled. As a
consequence of this there are three main issues to be considered when assessing an existing
structure:
The effect of possibly changed requirements to the structure on the structural performance.
Validation of the design assumptions and assessing the effect of possible deviations from
these on the structural performance.
Assessing the condition and residual capacity and service life of the structure.
Reasons for Reassessment
Following the foregoing the need for an assessment of an existing structure fundamentally
takes basis either in a change of the requirements to the use and/or requirements to the
structure and/or doubt in regard to whether the assumptions underlying its design are fulfilled.
Typical situations where the use/purpose of the structure is changed are thus:
Increased loading (e.g. higher traffic volume and/or higher axle loads).
Increased service life (the structure is still needed after the planned service life).
Increased reliability (due to increased importance of the structure for society).
Modification of the structure to accommodate modification in use (e.g. extra traffic lanes
on a bridge).
Typical situations where doubts may be raised in regard to the design assumptions are e.g.:
The structure has not been inspected for an extended period of time (damages, and
unforeseen degradation might have taken place).
Unexpected degradation has been observed (AKR, frost/thaw, fatigue, corrosion, etc.).
The structure has been subject to an accidental or otherwise non-foreseen extreme load
(excessive load, fire, earthquake, etc.).
Similar structure(s) exhibit unsatisfactorily performance.
New knowledge and revised design codes.
Framework for Structural Reassessment
In the reassessment of a structure it is useful to consider the exposure of the structure, the