The upcoming CEN Technical Specification (TS) on assessment of existing structures is to be related to the probabilistic concepts and fundamental requirements of the EN Eurocodes. The document should concern all types structures made of concrete, steel and other materials, exposed to all kinds of actions. The final draft of the Technical specification was already submitted to the technical committee CEN TC250. The principles of this document include general requirements, general framework of operational assessment, data updating, structural analysis (linear, nonlinear, dynamic), verifications (partial factors, assessment values, probabilistic methods, risk assessment), past performance, interventions and annexes (flowchart, time-dependent reliability, assessment of heritage structures).
The submitted contribution provides background information on the principles included in TS and their operational use. Particular attention is paid to specification of the target reliability levels and application of the appropriate values in engineering practice when adjusting the partial factors, specifying the assessment values and using probabilistic approach. It is shown that the reliability approach to assessment of existing structures provides prediction of the remaining working life of a structure. The target reliability level is commonly related to a convenient reference period (1 or 50 years) taking into account durability aspects and mutual dependence of the failures in subsequent basic time periods (usually one year). General principles are illustrated by assessment of a reinforced concrete structure.