ABSTRACT
Basically the current seismic design practice agrees with the principle of multi-level seismic design. According to this philosophy the building must resist minor earthquakes without significant damage, moderate earthquakes with repairable damage and major earthquakes without collapse. But in practice, the current seismic codes are involved with the minimal loss of life only. The usual procedure for checking the fulfillment of the requirements, that a seismic resistant structure has to posses, is based on elastic analysis under equivalent static lateral forces. These forces are defined by reducing the base shear forces by means of the so-called q factor, which takes into account the structural ductility and the seismic energy dissipation. The safety against the ultimate state is considered automatically verified, provided that the detailing rules and procedures, suggested by seismic codes, are satisfied.
