Reliability and redundancy under seismic loads

Structural redundancy is an important concept in structural performance and safety evaluation, yet it has not been clearly defined, and as a result, not well understood by engineers. This study investigates the various factors that have an impact on the redundancy of steel moment frames and dual (moment frame and shear wall) systems under seismic excitation. The emphasis is on effects of number of lateral force resistance components, member ductility capacity, strength variability and correlation, structural configuration, and uncertainty in the seismic excitation. A uniform-risk redundancy factor for design is proposed to achieve uniform reliability of structural systems with different degrees of redundancy.