Research On The Axial Pressure Properties Of Steel Tube Ultra-high Performance Concrete Short Columns

Ultra high performance concrete(UHPC)is a new kind of civil engineering material with many advantages such as extremely high strength and excellent durability.The combination of ultra high performance concrete and steel tube forms ultra high performance concrete filled steel tube(UHPCFST).UHPCFST is used as the bearing member,which provides strong support for the construction of super high-rise buildings and long-span structures with its extremely high bearing capacity.At present,in the research of UHPCFST,the analysis of circular UHPCFST short columns are mainly carried out,while a few of square UHPCFST short columns are analyzed,and lacks the comparative analysis of two kinds of cross-section members.In addition,The existing code formulas can be applied to the calculation of the bearing capacity of ordinary concrete filled steel tube and high strength concrete filled steel tube.Whether the code formulas can be applied to the calculation of the axial bearing capacity of UHPCFST short columns need further research.Based on the lack of comparative study on the axial compression performance of square UHPCFST short columns and circular UHPCFST short columns and the lack of corresponding bearing capacity calculation formulas,this paper uses the large universal finite element software ABAQUS to study the axial compressive properties and ultimate bearing capacity of square UHPCFST short columns and circular UHPCFST short columns.The main research results are as follows:(1)Based on the derivation method of the axial compression bearing capacity formula of ordinary concrete filled steel tube short columns,and referring to related research,the calculation formula function types for the axial compression bearing capacity of square UHPCFST short columns and circular UHPCFST short columns are established respectively.(2)The finite element models of square UHPCFST short columns and circular UHPCFST short columns under axial compression were established and calculated.The failure modes,load-displacement curves and ultimate bearing capacity of the simulation were basically consistent with those of the tests.(3)Under the influence of various parameters,the axial compression load-displacement curves of square UHPCFST short columns and circular UHPCFST short columns includes four stages: elastic stage,elastic-plastic stage,load drop stage and steady stage.When the research parameter is the same,the load-displacement curve of square UHPCFST short columns decrease faster and more widely.(4)At the middle section of UHPCFST short columns,the effective restraint areas of square steel tube for UHPC are mainly concentrated in the four corners and the core area,while the restraint area of circular steel tube for UHPC is uniform,and the stress is evenly distributed in the circumscribed direction.(5)The strength indexes of square UHPCFST short columns and circular UHPCFST short columns are greater than 1.The strength indexes decreases with the increase of the width(diameter)thickness ratio,and increases with the increase of the ratio of the strength of steel tube to the strength of concrete.The concrete contribution rate increases with the increase of the width(diameter)thickness ratio and the strength of concrete,and decreases with the increase of confining factor.The relationship between the concrete contribution rate and confining factor is established.The bearing capacity increases with the increase of the strength of concrete,the strength of steel tube,the thickness of steel tube and section size.When the research parameter is the same,the strength indexes,the concrete contribution rate and the ultimate bearing capacity of circular UHPCFST short columns are larger.(6)The existing code bearing capacity formulas of concrete filled steel tube are not applicable to the calculation of the axial compression bearing capacity of UHPCFST short columns,and the calculated values of the formulas and the simulated values have different degrees of deviation.Based on the established bearing capacity formula function types,the calculation formulas of axial bearing capacity of square UHPCFST short columns and circular UHPCFST short columns were obtained through data fitting.The bearing capacity formulas presented in this paper are effectively verified by the experimental values of the axial compression capacity of UHPCFST short columns.Compared with the formulas in other literatures,the calculation accuracy of the formulas presented is generally improved.