Prestressed Concrete Bridges in Germany - Overview of Current New Structures, Re-analysis and Research Activities to Preserve the Existing Infrastructure Network

Currently several major bridges are under construction in Germany, not only due to the construction of new roads and railway connections, but also because of the necessity to demolish and replace older bridges that no longer meet present requirements. Generally, the national infrastructure network is characterised by a relatively high average age of the existing bridges, a progressive increase in traffic volume (particularly with respect to the heavy traffic portion) and also a rise in weight of the individual vehicles and axle loads. In addition, several earlier design approaches for concrete bridges have been modified in modern codes, aiming to increase reserves in bearing capacity and to obtain more robust structures. Hence, an extensive assessment scheme was launched some five years ago, based on the so-called "Nachrechnungsrichtlinie" (guideline for bridge re-analysis and assessment, latest release 04/2015), issued by the Federal Ministry of Transport and Digital Infrastructure, which provides a systematic staged re-analysis approach (four levels of analysis) adapted to the special demands of existing structures. The present paper will firstly give a brief overview of selected new prestressed concrete bridges and related challenges and technical details in design and construction, including the utilisation of innovative materials and/or structural concepts. Subsequently, Germany's assessment strategy for existing bridges will be explained and relevant overall results and findings gained from the re-analysis scheme will be presented and discussed. Finally, current research activities focusing on a more realistic assessment of both actions (e.g. bridge-specific traffic loads) and resistances, i.e. the bearing capacity (particularly regarding the transmission of shear), will be addressed. In view of limited financial resources and the negative consequences induced by civil works in busy traffic infrastructure, it is of utmost importance to only strengthen (or even replace) those bridges where such measures are unavoidable and absolutely necessary.