Seismic Response Reduction Factors For Flexure-type Structures With Vertical Irregularity Under Strong Ground Motions

The seismic response reduction factors are not only the key parameter todetermine the inelastic response spectra for performance-based seismic design, butalso the key factor to determine the design seismic force for force-based seismicdesign. This work investigates the seismic response reduction factors of the verticalirregular flexure-type structures subjected to near-fault pulse-like ground motions.The main research contents and conclusions are as follows：(1) The effects of characteristic value of stiffness on the fundamental period,ductility demand, base strength demand and top displacement demand is discussed.The results are as follows: when the strength and stiffness of these two kinds structureare same, the fundamental period of flexure-type structure is larger than that ofshear-type structure due to the difference of the lateral mechanism. Top displacementdemand of flexure-type structure is larger than that of shear-type structures; on thecontrary the displacement demand of shear-type structure is larger than that offlexure-type structures. When keeping same fundamental period by adjusting thestiffness, the top displacement of two kinds of structures are almost same, and thedisplacement demands decrease. But the displacement demand of the shear-typestructure is still larger than that of flexure-type structures.(2) Influence of the fundamental period, storey number, ductility factor onseismic response reduction of two kinds of structures subjected to earthquake actionin hard soil are studied. The seismic response reduction factor of two kinds ofstructures increase with increasing ductility and decrease with increasing storeynumber, but there is no obvious regularity about the influence of fundamental periodon the seismic response reduction factor.(3) The seismic response reduction factor of flexure-type structure with verticalstrength irregularities subjected to velocity pulse-like ground motions is studied, andthe effects of the storey number, ductility ratio, irregularity ratio and velocity pulseeffects of ground motion on the seismic response reduction factors are discussed. Theresult shows that the seismic response reduction factors for irregular structures issmaller than those for regular structures. The modification factors decrease with decreasing irregularity, however, the ductility ratio and the storey number have littleinfluence on this modification. The results of pulse-like cases are smaller than thoseof non-pulse-like cases. Finally, based on the pulse-like ground motions and strengthirregularity, this paper average the results of the modification factor separately，whichcan accounts for the effects of vertical irregularity and velocity pulse on seismicresponse reduction factor in engineering application.