Safety Standard for Existing Structures

A safety philosophy for evaluating and upgrading existing structures is of great value. For a large part of the existing infrastructure and buildings the design life has been reached or will be reached in the near future. These structures need to be reassessed in order to find out whether the safety requirements are met. Not only for new structures but also for the existing stock the Eurocodes are starting point for the assessment of the safety. However, it would be uneconomical to require all existing buildings and civil engineering works like bridges to comply fully with these new codes and corresponding safety levels. The assessment of existing structures differs from the design situation on three main points. Increasing safety levels usually involves more costs for an existing structure than for structures that are still in the design phase. The remaining lifetime of an existing structure is often less than the standard reference period of 50 or 100 years that applies to new structures. For an existing building or bridge structure actual measurements with respect to geometry, material properties and behaviour under normal or design circumstances may be made in order to reduce uncertainty. In the design philosophy both economic arguments and limits for individual human safety play a role. This paper gives guidelines for establishing reliability indices for existing structures.