**4. Conclusions**

Construction methods and seismic protection techniques are interesting topics regarding multi-span viaducts characterized by steel-concrete composed deck.

A detailed design leads to the solution of many issues deriving from the structural altimetric and planimetric irregularity and from the high seismicity of the site.

The analyses have been performed applying the capacity design approach. Dissipative devices have been used against the seismic forces in order to grant and control that the piers remain substantially elastic.

For such purpose, each pier has been modelled taking into account its non-linear behaviour (theory of Takeda), simulating the stiffness at the cracking and plastic deformation status, in terms of moment curvature.

It has been verified that the system displacement request is lower than its capacity; the comparison between the ductility requested and the ductility available for the piers has been carried out according to the instructions provided by EC8-2 Annex E.

By the application of such design philosophy, it was possible to limit the forces at the base of the piers and, on the other side, the displacements of the decks and of the top of the same piers; the linear behaviour requirement of the metal superstructure under the effect of the seismic action was fulfilled as well.

At last, the comparison between the results of the FEM analysis performed using numerical and experimental data highlighted the correctness of the design hypothesis assumed.
