A POSSIBLE REVISION OF THE CURRENT SEISMIC DESIGN PROCESS

We present a possible Performance Based Seismic Design (PBSD) process grounded in a scenario based definition of the
\nseismic input. The proposed procedure aims to address the following considerations, arisen from the analysis of seismic
\nphenomena: a) any structure at a given location, regardless of its importance, is subject to the same shaking as a result of a
\ngiven earthquake, b) it is impossible to determine with precision when a future earthquake of a given intensity/magnitude
\nwill occur, c) insufficient data are available to develop reliable statistics for earthquakes. Following these considerations, the
\nseismic input at a given site - determined on the basis of the seismic history and the seismogenic zones, nodes and faults - is
\ndefined using the Neo Deterministic Seismic Hazard Assessment. Two different analyses are carried out at different levels
\nof detail. The first one (Regional Scale Analysis) provides the “Maximum Deterministic Seismic Input” as a response
\nspectrum at the bedrock (MDSIBD), similarly to what is proposed by the codes. The second one (Site Specific Analysis) takes
\nthe site effects into account, providing a site specific seismic input (MDSISS); This approach envelops uncertainties by
\nmeans of a wide range of NDSHA simulations rather than quantifying them probabilistically and provides realistic site
\nspecific seismograms that could be used to run time history analysis even where no registrations are available. Reviewing
\nthe standard PBSD procedure, MDSISS is always associated with the worst structural performance acceptable for a building
\n(Target Performance Level). Thus the importance of the structure (risk category) is taken into account by changing the
\nstructural performance level to check, rather than to change the seismic input. The procedure is a generalized enhancement
\nof what has already been applied for the seismic upgrading of several critical and essential buildings (e.g. schools) of the
\nTrieste Province (Italy).