Experimental Research On Seismic Behavior Of Exposed Steel Column Base And Seismic Performance Analysis Of Steel Frame

Steel structure has the advantage of high strength,light weight,good plasticity,toughness and good performance in dynamic load,in recent years,steel structure is widely used in civil and industrial buildings.In the steel structure,column base is an important node connected to the upper main structure and foundation,its mechanical properties directly affect the mechanical behavior of the main structure.Steel column base is widely used in low-rise steel structure owing to simple structure and construction convenient.Exposed column base is usually designed as rigid or pinned in engineering practice,however,the researchs show that the mechanical properties of column base is between rigid and pinned,that is semi-rigid.In order to study the mechanical properties of exposed column base,the quasi-static loading test adopted to research the mechanical properties of exposed column base in large deformation,The test parameters are the material of anchor rod,the number and the arrangement of anchor rods and the axial load.The strength,stiffness,ductility and dissipated energy are discussed.Through theoretical analysis and experimental results,the bearing capacity formula,stiffness formula and restoring force model of exposed column base are given.Through the establishment of 4-story 4-bay steel frame model,the nonlinear time history analysis is put out,the study mainly forcus on seismic fragility and collaps margin ratio of the steel frame,considering flakiness ratio of column,stiffness of base and failure mode.Studying the earthquake resistant behavior difference in semi-rigid design and rigid design,providing reference for the elasto-plastic analysis of steel frame.Through quasi-static test and steel frame analysis,the main research results are as follows:(1)The flexural bearing capacity of column base with 6 anchor bolts increased by 10%-20% than that with 4 anchor bolts;increasing the number of anchor bolt,dissipated energy increase by 10%-20% under large deformation;increasing the number of anchor bolt,the initial stiffness of column base increase aboult 20%.Column base with hot-rolled anchor rod showed good ductility with ductility factor larger than 4,Column base with cold-formed anchor rod has a reduction of ductility,which ductility factor is 2.42,Better use hot rolled anchor column foot ductility,ductility coefficient is greater than 4;Using cold unmoor bolt will greatly reduce the ductility of column foot,damage occurred suddenly,ductility coefficient is 2.42,the failure is unexpected,detrimental in anti-sesmic.(2)When column base under compressive axial force,the hysteretic loops are “flagshaped”,with significantly pinch effect,mortar layer is crushed in large deformation;while when column base under tensile axial force,the hysteretic loops are “shuttle-shaped”,base plate split from mortar layer absolutely,and anchor bolt is snapped.(3)The failure mode controled by the column base can reduce the damage of steel column,and reduce the demand for flakiness ratio of steel column;when the failure mode controled by the column,the anti-seismic performance of the frame is mainly associated with flakiness ratio of steel column,when fakiness ratio of steel column is larger,reduction of stiffness of column base can reduce the injury of column,improve the structural anti-seismic performance.