Redundancy in steel braced frames under seismic excitations.

摘要

The concept of a penalty for lack of redundancy and seismic load paths in a building was given birth in 1994 by the SEAOC Seismology Committee. The committee arbitrarily developed a transition formula between a factor of 1 for a redundant structure and 1.5 for a non-redundant structure and included the effects of the plan area of the structure.; Because the ductility of braced frames is not as good as that of moment frames, redundancy study on braced frames is more urgent. The objectives of this study are to clarify the definition of structural redundancy of braced frames and to develop a performance-based redundancy factor for braced frame design. Performance evaluation for 3-D structures subject to earthquakes is discussed as well as definitions of intensity measure for biaxial ground motions. IDA procedures and drawbacks of the state-of-art criterion of drift capacity are described.; Inverted-V bracing is the main concern in this study because of their popularity. The hysteresis behavior, overall buckling, local buckling and fracture life of a brace are investigated comprehensively. The effects of gusset plates and brace connections on the strength and ductility of bracing members are discussed. The Refined Beam Model and The Beam-Connector-Beam Model are used for modeling of bracing members and detecting brace fracture.; The dynamic displacement response of the 3-, 8- and 12-story buildings as well as brace fracture location and time are discussed. The drift capacities and drift demands as well as intensity capacities and intensity demands are determined for performance evaluations.; A new redundancy factor from probabilistic theory of performance evaluation is derived and determined for all of the calculated braced frames. The new redundancy factors are compared with the redundancy factors currently required by code. Fragility curves are also calculated for each building. Conclusions are drawn in order to contribute to future structural design.