Experimental Study On Axial Compression Performance Of Fly Ash Self-compacting Concrete Filled Steel Tubular Columns

The concrete-filled steel tube composite structure has excellent load-bearing performance and seismic resistance,which can maximize the advantages of good ductility of steel tube and high compressive strength of concrete.It overcomes the shortcomings of pure steel tubes easy to buckle and deform under load and concrete one-way stress brittle and is a structural form with excellent comprehensive performance.Fly ash self-compacting concrete has better workability and durability,and can also reduce cement consumption and consume industrial waste,meeting the requirements of green,environmentally friendly and sustainable development.Fly ash self-compacting concrete filled steel tubular columns have high loadbearing capacity,good seismic and fire resistance,and convenient construction without the need for formwork and vibration,they have broad application prospects in practical engineering.In this paper,the axial compression test of fly ash self-compacting concrete filled steel tubular columns is carried out by changing the parameters of concrete strength grade,outer steel tube type and internal structure form.A unified formula for calculating the axial compression load capacity of complex form concrete filled steel tubular columns is derived,and a universal finite element modeling method for complex form concrete filled steel tubular columns is established.The main research contents and conclusions are as follows:(1)Twenty-two different types of fly ash self-compacting concrete filled steel tubular columns were subjected to axial compression tests.To investigate the effects of each design parameter on the axial compression performance of fly ash self-compacting concrete filled steel tubular columns,the structural response and failure mode of each specimen under load were observed.The effects of various design parameters on its failure mode,load-bearing capacity,deformation performance,and other aspects were discussed.The results indicate that the type of outer steel tube determines the failure mode of the specimen.The failure mode of the outer circular steel tube specimen is upper middle shear failure,while the outer square steel tube specimen is upper middle multi-layer annular buckling failure.In general,the outer circular steel tube has a better restraint effect on the concrete and has excellent comprehensive performance.Incorporating internal structures and upgrading the concrete strength improved the load-bearing capacity of the specimens,but had no significant effect on the failure mode.Normally,the internal structure provides the effect of the inner layer of square steel tube,inner layer of circular steel tube,inner layer of H-shaped steel,and no structural measures in descending order.It is worth noting that the construction form of the outer square steel tube and the inner circular steel tube has an adverse effect on the load-bearing performance of the specimen,and the mechanism of its action still needs further study.(2)Considering the type of outer steel tube and the form of internal structure,a unified formula for calculating the axial compression load-bearing capacity of complex forms of steel tube fly ash self-compacting concrete columns is established.The theoretical calculation was carried out by three methods,namely superposition principle,consideration of inner steel tube restraint effect and unified formula for calculation of axial compression load capacity of complex form concrete-filled steel tubular columns,and the calculation results matched with the test results,indicating that the unified formula for calculation of axial compression loadbearing capacity of complex form concrete-filled steel tubular columns proposed in this paper has high accuracy and practicality,which can provide some reference for simplified calculation of axial compression load capacity of complex form concrete-filled steel tubular columns.(3)A general modeling method for finite element analysis of complex form concrete-filled steel tubular columns was established.The results of failure mode,stress nephogram,ultimate bearing capacity and so on obtained from finite element simulation match with the test results,and the force deformation and stress variation of each part can be obtained intuitively,which verifies the accuracy of the modeling method,and the modeling method proposed in this paper can be used for reference of relevant test research and engineering application.