The Study On Mechanical Properties Of Concrete-filled Circular CFRP-steel Meddle Long Columns Under Axial Compression

In order to explore the possibility of the application of new materials and their combined structural forms in modern building structures,this thesis further analyzes the mechanical properties of concrete-filled circular CFRP-steel middle long columns,and analyzes the influence of CFRP layers,concrete strength grade,steel tube wall thickness and slenderness ratio on its ultimate bearing capacity on the basis of the research of circular section concrete-filled steel tube and CFRP-confined concrete.In this thesis,concrete-filled circular CFRP-Steel middle long columns were made by pouring concrete inside and wrapping CFRP on the outer surface of the steel tube.While the elastic-plastic of the concrete-filled steel tube was worked effectively,the high tensile property of CFRP was used to enhance the axial compressive strength of the concrete-filled steel tube,so as to strengthen the ultimate bearing capacity of the concrete-filled steel tube and improve the flexural rigidity of the members.In addition,it can prevent the possibility of local buckling in the case of large lateral deflection.The specimen is analyzed by circular section,which is widely used in practical engineering.However,at present,there are few researches on the axial bearing capacity of concrete-filled circular CFRP-steel middle long columns,especially on the influencing factors of the ultimate bearing capacity of concrete-filled circular CFRP-steel middle long columns.The axial compression performance of concrete-filled circular CFRP-steel middle long columns is analyzed by experimental,theoretical and numerical simulation analysis method.The mechanical performance of this new composite structure is deeply explored.Its stress process,failure mode and axial compression ultimate bearing capacity are analyzed,and the basic calculation method of its ultimate bearing capacity is established,which provides strong support for its future engineering application and design.This thesis focuses on the following two aspects:（1）10 different concrete-filled circular CFRP-steel middle long columns were tested under axial compression.The mechanics characteristic,failure mode and ultimate bearing capacity of concrete-filled circular CFRP-steel middle long columns are discussed.The effects of CFRP layers,concrete strength,steel tube wall thickness and slenderness ratio on the ultimate bearing capacity are analyzed,which lays a foundation for the theoretical calculation of ultimate bearing capacity of concrete-filled circular CFRP-steel middle long columns.Based on the analysis of the test results,the longitudinal load-strain diagram of steel tube in mid-span,the circular load-strain diagram of steel tube in mid-span,the circular load-strain diagram of CFRP in mid-span and the lateral load displacement diagram of CFRP in mid-span is obtained.The analysis shows that the ultimate bearing capacity and stiffness of concrete-filled circular CFRP-steel middle long columns under axial compression are greatly improved compared with ordinary CFST.This proves that when subjected to axial load,the circular steel tube and carbon fiber sheet can work together more coordinately,the steel tube can play its own high ductility,and the carbon fiber sheet improves the bending stiffness of the member;increasing the number of layers of carbon fiber sheet,the ultimate bearing capacity of the middle long columns increases,and the ductility also improves;increasing the wall thickness of the steel tube,the bending stiffness of the middle long columns increases The results show that the yield strength and ultimate bearing capacity increase with the increase of concrete grade,and the ultimate bearing capacity of middle long columns can also be appropriately improved;with the increase of slenderness ratio,the ultimate bearing capacity of members decreases,so it is safer to choose concrete-filled circular CFRP-steel middle long columns with its height less than1 m.（2）Based on the above experimental study,a general formula for calculating the axial bearing capacity of concrete-filled circular CFRP-steel middle long columns is established,and the calculated results are matched well with the test results.In order to check the test results and calculation results,this thesis carries out the numerical simulation analysis of the test process,and the practical models of steel tube,concrete and carbon fiber reinforced plastic are selected.In this thesis,ANSYS finite element software was used to carry out finite element calculation on the axial compression test process of concrete-filled circular CFRP-steel middle long columns,and the load mid span deflection curve was obtained.Through the comparison,it is found that the results of numerical simulation can be in good agreement with the experimental results and theoretical calculation results,which proves the feasibility and applicability of using ANSYS to deal with such problems,and the correctness of the experimental results and theoretical calculation results.