Standardisation of seismic design

The first concepts for structural design in seismic areas, the subject of Eurocode 8 (EC8), were developed from experience gained in catastrophes such as the San Francisco earthquake in 1906 and the Messina earthquake in 1908.

At the very beginning, in the absence of experimental data, the method used was to design structures to withstand uniform horizontal accelerations of the order of 0.1g. After the Long Beach earthquake in 1933, the experimental data showed that the ground accelerations could be much higher, for instance 0.5g. Consequently, the resistance of certain structures could be explained only by the energy dissipation that occurred during the movement of the structure caused by the earthquake. The second generation of codes took into account on the one hand the amplification due to the dynamic behaviour of the structures, and on the other hand the energy dissipation. However, the way to incorporate this dissipation remained very elementary and did not allow correct differentiation between the behaviour of the various materials and types of lateral resisting systems.

he current third generation of codes akes it possible on the one hand to specify the ay to take the energy dissipation into account, according to the type of lateral resistance and the type of structural aterial used, and on the other hand to iden the scope of the codes, for instance by dealing with geotechnical aspects. Moreover, these new rules take into account the semi-probabilistic approach for verification of safety, as defined in EN 1990.

The appearance of displacement-based analysis methods makes it possible to foresee an evolution towards a fourth generation of seismic design codes, where the various components of the seismic behaviour will be better controlled, in particular those that relate to energy dissipation. Fro this point of view, in its present configuration, EC 8 is at the junction bettveen the third generation codes, of which it still forms part, and of fourth generation codes.

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