System reliabilities in steel structural frame design by inelastic analysis

Several steel design specifications worldwide have incorporated provisions for designing through inelastic analysis of overall system behavior. However, requirements for minimum system reliability have been implemented in such design-by-inelastic analysis methods through a simple adaptation of resistance factors originally developed from member reliability considerations. This paper examines system resistance factors through a system reliability analysis of two steel moment frames subjected to combined gravity and wind loads. The frames are designed using second-order inelastic analysis and their strength and serviceability reliabilities are evaluated. The effects on the system reliabilities of system resistance factor and wind-to-gravity load ratio are examined. The paper also identifies some research issues that should be addressed prior to implementing a system reliability-based design methodology.