Experimental And Theoretical Research On The Mechanical Property Of Reinforced Concrete Filled Steel Tubular Columns

With the development of the high-rise building structure and the demand forseismic, fire resistant, configuring reinforced steel bar in large-diameter concretefilled steel tubular structure has become an inevitable choice. The reinforcedconcrete filled steel tubular (RCFST) can be constructed by configuring steel barsinto concrete filled steel tube (CFST). The RCFST has a better bearing capacity,ductility and seismic performance. The generation, application and development ofRCFST structure conform to the development trend of structural engineering. Itsmechanical properties were mainly investigated in this thesis.Based on the unified theory, the RCFST is regarded as a single material and itscomposite compressive strength is obtained. At present, research on CFSTcomposite compressive strength is very mature. By considering the influence ofsteel bars on the basis of CFST, the RCFST composite compressive strength can bederived. The longitudinal steel bar improves the composite compressive strengthdirectly, while the hooping contributes to the composite compressive strengthindirectly by adding the constraint effect to the core concrete. The unified formulaof the RCFST composite compressive strength is given based on the above way.The bearing capacity of the RCFST with circle cross-section under various loadconditions is deduced by using the axial composite compressive strength.Specifically, the bearing capacity of the axial compressive short column, the axialcompressive long column, the bending member and the compressive-bendingmember is studied.Axial concentric compressive model tests have been performed to examine themechanical properties of circle-section RCFST short columns and long columns.The test includes axial concentric compression tests of four circle cross-sectionRCFST short columns and a control sample, circle cross-section CFST short column;axial concentric compression tests of two circle cross-section CFST long columnsand a control sample, circle cross-section CFST long column. Tests on shortcolumns mainly study the influence of the reinforcement ratio and the hooping spaceon the bearing capacity of members. And the tests of long columns study theinfluence of reinforcement ratio on the bearing capacity. Tests show that the bearingcapacity of short columns has improved after configuring reinforced steel bars and ishigher than the sum of the bearing capacity of CFST and steel bars. The bearingcapacity of short columns increases with the increasing reinforcement ratio, and theration of the increment of the bearing capacity and the reinforcement ratio remain constant. However, the increment of the bearing capacity of the short columnincreases after shorting the hooping distance. The configuration of the reinforcedsteel bar in long columns contributes to improving the stable bearing capacity. Withthe increment of the increasing reinforcement ratio, the bearing capacity increaseswhile the ductility is not influenced. The test result conforms to the formula deducedin the earlier part.At last, the finite element model of circular section RCFST columns is built usingthe large scale general-purpose Finite Element software ABAQUS. The rationalityof the FE model is verified by comparing simulation with experimental results andthe formula results. Parameter analysis, including the steel ration, the reinforcementratio and the hooping space, is also performed to study the influence on the axialcompressive bearing capacity of short columns. The results show that with theincrement of the reinforcement ratio, the increment of the bearing capacity due tothe exaltation of the steel ration is mitigated. And the increment of the bearingcapacity is proportional to the increment of the reinforcement ratio. When thehooping distance is short, the bearing capacity is improved to some extent. But thedecrement of the bearing capacity reduces with the increasing hooping distance.Therefore, the influence of the hooping distance on the bearing capacity could beneglected when the hooping distance increases to one value.