Seismic design of bridges according to EC8-2

Once the long process of writing and validation has been completed, the Eurocodes have now entered their operational phase. The design and dimensioning of engineering structures are determined by the Eurocodes:

• EC0 for calculation bases ;

• EC1 for loads ;

• EC2, EC3, EC4 and EC5 for materials commonly used in engineering structures;

• EC7 for geotechnical aspects.

One of the major new features of the Eurocodes is Eurocode 8. Entirely devoted to earthquake-resistant design, and placed at the same level as the other main Eurocodes, it incorporates the latest scientific and technological advances in knowledge and consideration of seismic risk in the design and dimensioning of engineering structures (definition and representation of the seismic hazard, methods for analyzing the dynamic behavior of structures, special earthquake-resistant protection devices, etc.).

The old PS 92 rules and, in particular, the AFPS 92 guide for earthquake protection of bridges, have been rendered obsolete by these standards. The various regulatory texts (decree of 1991 and "bridge" decree of September 15, 1995) have been revised to refer to Eurocode 8.

While the main design principles are broadly in line with the practices inherited from the application of the old PS92 rules, several significant changes should be noted. Compared with these previous design rules, they significantly modify the habits and practices of engineers in charge of dimensioning structures, with regard to actions linked to the consideration of earthquakes. In particular, the seismic zoning of France has been revised: on the one hand, to incorporate new scientific knowledge on national seismicity; on the other, to take into account the probabilistic philosophy of the Eurocodes, and Eurocode 8 in particular.

This article is largely based on the guide "Bridges in seismic zones – Design and dimensioning according to Eurocode 8", written by the Service d'études sur les transports, les routes et leur aménagement (Sétra), and the Centre d'études techniques de l'équipement (CETE) Méditerranée, technical departments of the French Ministry of Ecology, Sustainable Development and Energy, responsible in particular for transport infrastructures. It presents the main changes brought about by the new legislation in design practices and the analysis of the seismic behavior of engineering structures. It attempts to assess the consequences in terms of difficulty of implementation, level of performance or safety of structures and associated costs.