Standards for the assessment of existing structures: real need or caprice of code makers?

Abstract

The assessment of existing structures is an urgent issue of great economic importance in an increasing number of countries around the globe, as in many places more than half of the total construction activity involves existing buildings, bridges and other civil engineering works. Currently, the Eurocodes, which will be used in all member states of the European Committee for Standardization, CEN, and possibly in more and more countries outside this space, are mainly focused on designing new structures. The use of design-oriented methods to assess existing structures often leads to a high degree of conservatism. This has serious economic, ecological and socio-political consequences if satisfactory structures are condemned as unsafe, thereby leading to an unnecessary investment of resources in retrofitting or replacement and the associated dismantling. For this reason, assessing existing structures often requires the use of refined methods that go beyond the scope of the design codes for new structures. Therefore, in the last 20 years, methods for assessing existing structures have been developed in many countries on a national level. However, they have not yet been coordinated and are not widely used in daily practice. There is therefore an urgent need to merge the various national approaches into a generally accepted, coherent and harmonized set of rules for existing structures that complements those for the design of new structures. As a result, CEN took the initiative to start a project to develop new European technical rules for the assessment and retrofitting of existing structures. It was decided to achieve the development of new parts of the Eurocodes in three steps, two of which have already been completed in relation to existing structures: preparation of a Scientific and Policy Report and, after its acceptance by the National Standardization Bodies of the member states, conversion into a CEN Technical Specification. In the context of the third step, the conversion of the Technical Specification into an EN Eurocode Part, relevant differences between assessment and design from the point of view of structural reliability are discussed in this paper and some needs for further code provisions with regard to existing structures are identified.