Comparative Study On Strengthening Measures For Concrete- Filled Thin-walled Square Steel Tubular Columns

Concrete-filled thin-walled steel tubes are the composite members formed by filling concrete into thin-walled steel tubes.However,the compressive performance of core concrete cannot be completely used as the walls of thin-walled steel tube are prone to local buckling.As a result,scholars have proposed the strengthening measures for the concrete-filled thin-walled steel tubes to delay or avoid local buckling of thin-walled steel tube,and simultaneously to provide reliable constraints to core concrete.Currently,the main strengthening measures for concrete-filled thin-walled square steel tubes include: longitudinal strengthening,transverse strengthening,hoop strengthening,etc.However,under the same condition,the difference in performance of concrete-filled thinwalled square steel tubes with different strengthening measures is unknown,which makes it difficult for designers to choose.Therefore,it is of great significance to study the behavior of concrete-filled thin-walled square steel tubular columns under different strengthening measures and evaluate the advantages and disadvantages of each strengthening measure comprehensively for the application of concrete-filled thin-walled square steel tubular members in practical projects and further research.In this thesis,the axial compressive behavior and feasibility of concrete-filled thin-walled square steel tubular stub columns with different strengthening measures are compared and studied,and the main works are summarized as follows:(1)The axial compressive tests on 14 concrete-filled thin-walled square steel tubular stub columns are designed and completed.The failure patterns,load versus deformation curves and mechanical indexes,such as bearing capacity,axial compression stiffness and ductility coefficient,are obtained to investigate the performance of concrete-filled thin-walled square steel tubular stub columns with different yield strength of steel and strengthening measures.(2)The bearing capacity of concrete-filled thin-walled square steel tubular stub columns with different strengthening measures is calculated by the simplified method provided in the norm to evaluate the accuracy of the existing formulae.(3)Based on the reasonable constitutive model of steel and core concrete,a finite element model of concrete-filled thin-walled square steel tubular stub columns with different strengthening measures is established by using the general software ABAQUS.The failure patterns,load versus deformation curves,bearing capacity and axial stiffness of the simulated specimens are in good agreement with the test results.(4)From the point of view of mechanical properties and cost per unit carrying capacity,the advantages and disadvantages of various strengthening measures are comprehensively evaluated by a comparison of concrete-filled thin-walled square steel tubular stub columns under five types of strengthening measures,which can provide a reference for relevant engineering practice and regulations.