ABSTRACT
The current procedure for seismic design of new building structures is termed force-based design (FBD) since it uses seismic forces as the main design parameters. This design method (EC8 2004) demands the design of the building against structural failures which might endanger human life on the basis of recommended constant values of the behavior (or strength reduction) factor, q, and checks deformations beyond which service requirements are no longer met after the detailing of the structure. The tentative guidelines for performance-based seismic design (PBSD) according to SEAOC (1995) present two alternative forms of displacement-based design of new structures, namely, the direct displacement-based design (DDBD) method and the equal-displacement-based design (EDB) one. Contrary to FBD, those displacement-based procedures employ the maximum interstorey drift ratio (IDR) for describing performance levels and also treat user-defined values of the IDR as input variables for the initiation of the design process. However, these methods are limited in that they are applicable only to regular frames, adopt an equivalent linear (DDBD) or nonlinear (EBD) SDOF representation of the building, do not recognise basic differences in the response due to different lateral load resisting systems and try to control both structural and non-structural damage by imposing limits only on drift demands.
