Structural redundancy of dual and steel moment frame systems under seismic excitation

The extensive investigation of structural failure after Northridge earthquake showed poor structural performance due to brittle member behavior and improper design. For example, the brittle steel connection fractures were totally unexpected of the highly regarded “ductile” systems. The lack of system ductile capacity and redundancy could lead to system instability and collapse. Since then, the design for redundancy has become a serious concern of both researchers and practitioners. Most reliability and redundancy studies in the past, however, have been limited to ideal simple systems. Structural redundancy under stochastic loads such as earthquakes has not been thoroughly investigated and hence not well understood or clearly defined, which could lead to misunderstandings and confusions among structural engineers.; In this study, the redundancy of five-story and ten-story one-way and two-way dual systems of RC shear walls and three-story and nine-story special moment resisting frames (SMRF) is investigated in terms of system reliability. Major factors affecting redundancy considered include structural configuration (number of bays in lateral load resistance system, number and layout of shear walls, and so on), ductility capacity, uncertainty and correlation of shear wall strength. The redundancy of truly ductile SMRF systems of different configurations is also examined. A 4 x 4 bay and a 6 x 6 bay buildings of the same floor area but different numbers and sizes of beams and columns are designed and analyzed. In addition, three SMRF, 1 x 1, 2 x 2, and 3 x 3 bay systems, with torsion are investigated to examine the effect of ductile and brittle beam-column connection behaviors.; The proposed uniform-risk redundancy factor is then compared with the reliability and redundancy factor (ρ) in the 1996 SEAOC Blue Book, NEHRP 97, and UBC 97, which depends on the system configuration only. The results show the inadequacies of the latter approach in describing the redundancy of a building system due to its failure to address other important factors such as demand and capacity uncertainty as well as brittle versus ductile member behavior. Finally, the reliability of design based on the uniform-risk redundancy factor is verified for the 5-story, one way dual systems.