Seismic input in the structural design: considerations and application to the italian territory

Some recent seismic events pointed out the necessity to revise our way of seismic analysis of structures. But what do structural engineers need to design anti-seismic structures? The first step is the analysis of the seismic input, defined by means of the basic hazard analysis and of the local seismic response. Once the description of the seismic hazard is known, the choice of the protection degree should be made on the basis of economical evaluations. Furthermore, the uncertainties about the local seismic response could be very important. The second step is the structural modeling and analysis, whose suit-ability depends on how good is the description of the material behavior, geometrical characteristics of the structure, and its behavior both in elastic and inelastic ranges. This is accounted for by means of the behavior factor, whose definition and use are quite delicate and often not necessary, especially in low-to medium-seismicity areas, as demonstrated by means of a comprehensive numerical analysis on the construction costs of reinforced concrete buildings. In this article, some important issues are discussed and some proposals are given to improve the technical codes and hence the safety of structures against earthquakes. The seismic input to be used in the retrofit of existing buildings is also discussed.