Study On The Mechanical Behavior Of Ultra-high Performance Concrete Filled High Strength Steel Tubular Short Columns Under Axial Compression Loads

Ultra-high Performance Concrete（UHPC）,as a new type of cement-based material,has been concerned by researchers for its superior mechanical properties and good durability,which was widely used in the fields of bridge,architecture,municipal engineering,etc.People poured UHPC into the high strength steel tube to form a new composite structure,the Ultra-high Performance Concrete filled high strength steel tube（UHPCFHSST）,which not only improved the brittle failure mode of UHPC under high stress,but also delayed the local buckling of the steel tube,ensuring the full use of the mechanical properties of the two materials.It is especially suitable for super high-rise buildings,long-span bridges,overloading structures.With the development of modern building structure transferring to towering,long span and heavy load,this new type of structure has potential research and application value.At present,the research on Ultra-high Performance Concrete filled steel tube component is mostly concentrated on the circular and square sections,and the crosssectional dimensions of related components are relatively small.There are few researches on specimens with larger cross-sectional dimensions and hexagonal cross-sections.Relying on the National Natural Science Foundation of China,this thesis took the UHPCFHSST short column as the research object,and studied its axial compression performance based on experimental research and finite element analysis.The main research contents and results are as follows:（1）Circular Ultra-high Performance Concrete filled high strength steel tube（CUHPCFHSST）,square Ultra-high Performance Concrete filled high strength steel tube（S-UHPCFHSST）and hexagonal Ultra-high Performance Concrete filled high strength steel tube（H-UHPCFHSST）short columns axial compression test were carried out.The failure mode,bearing capacity,load-displacement curve and load-strain curve of each specimen were obtained,and the mechanism of UHPCFHSS short column under axial compression was analyzed.（2）The finite element model（FEM）was established,whose reliability was verified by comparing with the tests in this thesis and relevant literatures.When axial load was applied on the short column,the stress distribution variation was analyzed.The effects of steel strength,concrete strength and steel pipe thickness on the bearing capacity and loaddisplacement curve of the specimens were systematically studied by using finite element analysis.（3）The calculation formula of axial compression bearing capacity of the three types of specimens were proposed respectively by combining the relevant design methods of concrete filled steel tube.This formula was adopted to predict the finite element analysis results and test results,and compared with that calculated with the existing formulas.It is shown that the formula proposed in this thesis has good accuracy and stability,which can provide reference for engineering design.