Theoretic Study On Compression Characteristics Of Composite Column Of Concrete Filled Steel Tube

With the development of modernization in our country, construction technology matures,the construction of large span bridges can be achieved. As a new type of steel-concretestructure, concrete filled steel tubular columns (CFSTC), which shows a powerful bearingcapacity, shows a favorable tensibility performance and the overall economic efficiency, hasbeen widely used as an ideal choice for pier design in foreign countries. However due to thelittle systematical research on the CFSTC, and it seriously hinders the development andpromotion of the combination of concrete filled steel tubular column.Based on the normal section bearing capacity of concrete filled steel tube and theformula of reinforced concrete, the section bearing capacity formula of concrete filled steeltubular columns (CFSTC) is proved through the principle of superposition. Compared to theformula of a small eccentricity test results, the error is in the acceptable range. On the basisof previous test the specimens selected is the same with the test on Size and materialmechanical properties. Then an onlinear finite element model is presented and acorresponding numerical analysis is performed. Under axial compression the compressionmechanism of Steel concrete composite columns and the affection of ultimate bearingcapacity produced by each part of CFSTC are dicussed. Then draw some useful conclusionsto guide engineering practice.The study showed that: compared to reinforced concrete columns concrete filled steeltubular columns (CFSTC) have higher material utilization and greater carrying capacity andbetter ductility Under axial compression. When axial displacement is the same, the CFSTChave a higher bearing capacity. When axial force is the same, the CFSTC have a smallerdisplacement and better ductility; bearing capacity is increased as the position coefficientincreases, but the pipe diameter should not be too large, the diameter of CFSTC generallyare90~~100mm smaller than the cross-section side length. Comepared to improvingstrength grade of core concrete, Improving the concrete filled steel tubular columns stirrupsconfined concrete strength grade can get a larger carrying capacity. The longitudinalreinforcement of CFSTC is not the main object of carrying, but form to steel cage to constrainfor concrete with stirrups, it increases the carrying capacity of concrete and plastic to avoidbrittle failure.The study showed that: the steel pipe of CFSTC have a small contribution to the stiffnessof composite columns in the early loading under Small eccentric compression. bearingcapacity is increased with increasing of the position coefficient. when the diameter outsideSteel pipe and cross-section reaches a certain size ratio and the ratio is greater than0.518, thecarrying capacity has been increased, but the stiffness of CFSTC is decreased and the change of ductility have no regularity.The yield strength of CFSTC is increasing with increasing ofthe the ferrule coefficient and the ultimate bearing capacity have little change, the ductilityperformance is decreasing with of increasing the ferrule coefficient. Improving the concretefilled steel tubular columns stirrups confined concrete strength grade can get a larger carryingcapacity. The ultimate bearing capacity of the concrete filled steel tubular columns isincreasing with the decreasing of stirrup spacing. Encryption stirrups can significantlyimprove the ultimate bearing capacity in the end of concrete filled steel tubular columns.