Reliability of uncertain inelastic structures under earthquake excitation

The assessment of safety for structures subjected to earthquake excitation is a time-variant reliability problem whose practical solution, when the structure behaves inelastically and uncertainty in the mechanical parameters is taken into account, is traditionally sought by means of simulation. In this paper the feasibility of an alternative solution based on the first order reliability method is explored. The problem is expressed in terms of first-excursion event within a conceptual framework, established in recent years, in which random vibration problems are discretized to make them tractable by the well-established methods of time-invariant structural reliability. The necessary extensions to apply the methodology to reinforced concrete frame structures are presented. Applications to a simple spring-mass system and to a complete three-dimensional bridge structure are presented.