Experimental And Theory Studies On Axial Compression Performance Of Steel Reinforced Concrete Mega- Columns With Different Cross-sections

There are many projects using steel reinforced concrete mega-columns in megastructures of super high-rise buildings.Taking into account the characteristics of the building plan and the structural force requirements,the section shape and construction of steel reinforced concrete mega-columns sometimes vary greatly in different buildings.In this thesis,experimental and theory studies on the axial compression performance of special-shaped section and circular section steel reinforced concrete mega-column models are carried out,taking steel reinforced concrete mega-columns in super high-rise mega-structure as prototypes.The main works and contributions are shown as below:1.Experimental study on the axial compression behavior of 6 steel reinforced concrete mega-column model specimens were conducted under repeated axial load.All the specimens were divided into 3 groups: 1/5.3-scaled Wuhan Greenland Centro rightangled trapezoidal section steel reinforced concrete mega-column model specimens with embedded irregular cross-shaped steel with flanges;1/8.8-scaled Dalian Greenland Center pentagonal section steel reinforced concrete mega-column model specimens with embedded separated rectangular steel tubes;1/4-scaled Chengdu Greenland Center Tower circular section H-shaped steel reinforced concrete megacolumn model specimens.Concrete strengths of each group of the specimens were C55 and C75.The failure mode,axial load-displacement curve,bearing capacity,ductility,energy dissipation capacity,restoration capacity and strain development of each specimen were analyzed.The effects of cross-section shape and construction on the axial compression performance of steel reinforced concrete columns were illustrated.2.Section analysis method was used to perform nonlinear theoretical analysis on the axial compression behavior of steel reinforced concrete columns.The concrete was divided into different areas,the confinement effect of stirrups and steel on the concrete was analyzed,and the constitutive model of the concrete in different areas was established.The predicted axial compression load-displacement curves were compared with the test curves,and good agreement was obtained between the two.3.The finite element model was established and the finite element analysis of the axial compression performance of steel reinforced concrete columns was carried out using software ABAQUS.The axial compression load-displacement curves and damage diagram of concrete and stress diagram of steel were obtained,and the damage development process of the specimens was analyzed.The calculation results were in good agreement with the test results.The effects of volumetric stirrup ratio,steel ratio,steel strength,and concrete strength on the axial compression performance of steel reinforced concrete columns with different cross-sections were analyzed and the force mechanism were revealed.Main conclusions:(1)The stiffness degradation of the specimens under the axial compression load can be divided into four stages: elastic stage,elastic-plastic stage,descending stage,and softening stage.The axial compression bearing capacity of the specimens increased with the increase of concrete strength,while the ductility decreased with the increase of concrete strength.(2)Based on the section analysis method,a predictive full-process axial compression load-displacement analysis model was proposed for steel reinforced concrete columns,taking into account the confinement effect of stirrups and steel on the concrete.The calculation results show good agreement with the test results.(3)With the increase of volumetric stirrup ratio,steel ratio and yield strength of steel,the ultimate bearing capacity and ductility of the specimens increased significantly.