Concepts and design standards for earthquake resistant buildings

In most seismic regions, the adoption of construction techniques designed to reduce the risks associated with earthquakes appears to go back a long way. Excavations at the Taxila site in Pakistan, for example, revealed the need to reinforce foundations when the city was rebuilt after the earthquake of 25 AD. Similarly, in the Byzantine period, radical changes in construction methods were observed in several Syrian and Anatolian cities (reduction in house height, reinforcement with wooden frames, elimination of unreinforced brick walls). In China, Japan and among Inca monuments, there are also examples of ancient buildings designed with seismic risk in mind. These ancient examples bear witness to the fact that architectural concepts and building statics were mastered by Man long ago.

But it is only very recently that this mastery has included :

• on the one hand, the development of calculation tools to quantify the stresses induced in buildings by earthquakes;

• formalizing the rules to be followed in construction projects.

The aim of this article is to present the evolution of these rules, detailing the concepts behind the codes currently in force. In particular, the why and how of the "global plastic mechanism" objective, which underlies the rules promoting local and global ductility of structures. These are defined and examples of their practical implications are shown. Desirable architectural arrangements are also described. Observations made after recent earthquakes that are likely to further improve building design are compiled.

Finally, we outline the legislative and regulatory framework for seismic prevention in force in Europe, and its specific aspects in France.