For a large part of the existing buildings and infrastructure the design life has been reached or will be reached in the near future. These structures might need to be reassessed in order to investigate whether the safety requirements are met. Current practice on the assessment of existing concrete structures however needs a thorough evaluation from a risk and reliability point of view, as they are mostly verified using simplified procedures based on the partial factor method commonly applied in design of new structures. Such assessments are often conservative and may lead to expensive upgrades. Although the last decades reliability-based assessment of existing concrete structures has gained wide attention in the research field, a consistent reliability-based assessment framework and a practically applicable codified approach which is compatible with the Eurocodes and accessible for common structural engineering problems in everyday practice is currently missing. Such an approach however allows for a more uniform, more objective and probably more widely applied assessment approach for existing concrete structures. Hence, in this bulletin two different partial factor formats are elaborated, i.e. the Design Value Method (DVM) and the Adjusted Partial Factor Method (APFM), enabling the incorporation of specific reliability related aspects for existing structures. The DVM proposes a fundamental basis for evaluating partial factors whereas the APFM provides adjustment factors to be applied on the partial factors for new structures in EN 1990. In this bulletin both methods are elaborated and evaluated and a basis is provided for decision making regarding the target safety level of existing structures.

The first part of the report is devoted to linear elements (beams, columns) and includes chapters on shear and flexure in beams, ultimate limit state design of prestressed beams, and of reinforced concrete members under combination of bending with axial load and shear, of beams subjected to torsion, and a chapter on shear design based on truss models with crack friction. The second part treats two-dimensional elements and includes background information on ULS design of wall, shell, and slab elements. lt concludes with a chapter on axisymmetric punching of slabs.

The report has been prepared by the Joint Working Group on High Strength/High Performance Concrete, set up by CEB and FIP and comprising 15 experts from Europe, North America, Japan and Australia. Part one 'Recommended Extensions to Model Code 90' identifies the lacuna in existing regulations and proposes supplementary or alternative solutions to be applied with caution for concrete grades above C 50. In order to facilitate its use the report is edited in two columns following the numbering of the CEB-FIP Model Code 1990. It will be presented for approval to the 30th CEB Plenary Session in Berlin, September 1995. Part two identifies the research needs resulting from those clauses of Model Code 90 which needed amendments. Also more basic research needed for a better understanding of mechanical, physical and chemical processes which cannot be connected directly to a short-term application has been included."--Back cover.