Effect Of Long-link EBF Mechanism On The Seismic Performance Of CBF

Concentrically braced frames(CBF)is a kind of dual-lateral-force-resistent system.This system can resist lateral force including wind in elastic stage.However,a vertical unbalanced force may emerge in the intersection point of tensile brace,compressive brace and horizontal beam under strong earthquakes and thus the lateral stiffness of structure may decrease.It is recommended by scholars that horizontal beam should be strengthened to resist the unbalanced force but benefit of this phenomenon is ignored by most of the scholars.In this phenomenon,after the failure of one brace,the other brace no looger fail and a trianglar substructure is formed by the brace,beam and column.The beam starts to consume energy and CBF become ‘eccentric braced frame' and long link EBF mechanism is formed.The seismic energy is dissipated by this mechanism and capacity reserve of structure is improved.The purpose of this paper is to discuss the failure mechanism and collapse resistant capacity of CBF with long link EBF mechanism.The main work can be summarized as :(1)Brifly introduce two failure mechanism from CBF to ‘EBF' and compare and analyze failure mode in two failure mechanism.(2)Design two 6-story CBF with different brace parameters and Incremental Dynamic Analysis(IDA)is made under 20 far-field earthquakes.Discribe the inelastic deformation in dynamic analysis with time history analysis result considering the collapse resistant capacity effect of long link EBF mechanism to CBF and the structural damage evolution process is analyzed by several earthquake waves.(3)Introduce the evaluation method of collapse abundance and calculate the structural collapse abundance under rarely occurred earthquakes.The vulnerability curve is derived and collapse resistence capacity is quantificated in different failure modes.