Study On Seismic Behavior Of Encased Square Steel Tube Column Base Connections

The Column base is an important joint between column and cap,which plays a decisive role in the structural safety of the upper structure.The column base forms mainly include exposed type column base,embedded type column base and encased steel column base.Earthquakes are mainly important factors affecting for the safety of building structures.At present,various buildings have adopted the encased steel column base to resist the damage of earthquakes.The encased steel column base not only can bear the vertical force,but also can resist the damage of the horizontal force.Related scholars just do simple research content about the encased steel column base.The research content of the encased steel column base mainly focuses on the encasing height and the encasing thickness.Few studies have been done on the restraint form and structure form of the encased steel column base.Related issues about this type base have not been resolved.Therefore,the seismic performance of nine square steel tube column base was studied and mainly completed the following work:(1)Nine square steel tube column base specimens were tested under low frequency cyclicing load to study the effect of the encasing height,thickness,stud layout,stirrup,enclosing steel tube,and in-pipe concrete on the seismic performance.Analysising the hysteretic curve,moment-curvature cuve,skeleton curve,stiffness degradation,ductility and energy dissipation of specimens according to the test results.(2)The specimens with steel tube layouted are effectively restrained for the concrete of the encased reinforced concrete through analysis and comparison.The layout of stud can effectively strengthen the connection between square steel tube column and reinforced concrete.And the specimens with the studs are better than others about the ductility and the energy consumption.The bigger height of the enclosed concrete,the better force bearing and energy dissipation capacity.And the greater thickness,the stiffness is reduced faster,but the ductility is not much different.For the specimens without steel tube layouted,the concrete cracking is more serious.The specimens with the steel ring stirrups show similar results in terms of ductility and energy consumption,and the specimens that change the stirrups show similar results in terms of ductility and energy consumption.However,due to the role of studs and stirrups,the bearing capacity is large,indicating that only the addition of steel tube layouted cannot improve the seismic performance.(3)According to the test data,the axial force distribution coefficient is carefully divided.Based on the axial force distribution coefficient,the flexural capacity and shear capacity of each test piece were calculated by the derivation formula of the bending capacity calculation and the bending resistance of the encased reinforced concrete referencing to relevant literature.After the introduction of the axial force distribution coefficient,the actual value of the flexural capacity is close to the theoretical value.(4)Pushover analysis was carried out by using ABAQUS software for 4 representative specimens and compared with the experimental results,the two results are in good agreement.The peak load of each test piece is consistent with the actual value.The stress distribution nephogram and the damage of the test piece have the same characteristics and have certain reference value.