Experimental Study Of Mechanical Properties Of Composite-sectioned Stainless CFST Columns Filled With Demolished Concrete Lumps

The application of recycled concrete with demolished concrete lumps in composite concrete-filled steel tube section can take advantage of good restraint effect and ductility of circular steel tube,and help to make up for the defects of demolished concrete lumps.In this paper,the mechanical properties of self-compacting recycled concrete with demolished concrete lumps standard specimens and the mechanical properties of composite-sectioned stainless CFST columns filled with demolished concrete lumps under axial compression and eccentric compression are explored.The research contents and conclusions of this article are as follows:1.The uniaxial compression tests of 60 self-compacting recycled concrete with demolished concrete lumps standard specimens were carried out to investigate the influence of the replacement rate of DCLs and the strength of new and old concrete on the mechanical properties of the specimens.Test results show that:(1)The new concrete and old concrete lumps are well combined,and there is no failure of the interface between the new and old concrete;(2)The compressive strength,modulus of elasticity,peak strain and Poisson's ratio of specimens with low strength DCLs(26.7MPa)decreased with the increase of replacement rate of DCLs,while the compressive strength of specimens with high strength DCLs(87.6MPa)increased slightly;(3)The Poisson's ratio of self-compacting recycled concrete specimens with DCLs is between 0.205 and 0.221,with an average value of 0.214,which is similar to that of ordinary concrete.2.During the axial compression test of 16 composite-sectioned stainless CFST columns filled with DCLs,the influence of the replacement rate of DCLs,the ratio of diameter to thickness and the strength difference between old and new concrete on the mechanical properties of the specimens have been investigated.The results show that:(1)The failure process and failure mode of composite-sectioned stainless CFST columns filled with DCLs are similar to that of ordinary composite-sectioned stainless CFST columns,and the internal circular steel tube shows obvious shear failure;(2)The composite-sectioned stainless CFST columns filled with DCLs has good ductility and residual bearing capacity.At the end of loading,the specimen can still bear more than 64% of the peak load;(3)The bearing capacity of the specimen decreases slightly with the increase of the replacement rate of DCLs,and the maximum reduction of the bearing capacity is about 6.8%;(4)Using the assumption of direct superposition or taking into account the bearing capacity of the circular cross section multiplied by the reduction factor,the calculation results of the obtained bearing capacity agree well with the test results.3.The eccentric compression tests of 19 composite-sectioned stainless CFST columns filled with DCLs was carried out,the effects of the replacement ratio,eccentricity and the ratio of diameter to thickness on the eccentric compression performance of the specimens were investigated.The test results show that:(1)The eccentric compression failure process,failure morphology,load-axial displacement curve and load-span lateral deflection curve shape of composite-sectioned stainless CFST columns filled with DCLs are similar to those of a normal composite-sectioned stainless CFST columns,and the internal circular steel tube is bent in sinusoidal half wave shape,and the concrete in the tensile side of the circular steel tube has obvious transverse cracks;(2)The bearing capacity of the composite-sectioned stainless CFST columns filled with DCLs decreases with the increase of the eccentricity,and the decrease ranges from 35.4% to 43.1%;(3)The superposition method and the existing formula are used to calculate the eccentric compression bearing capacity of the specimen,and the calculated results are in good agreement with the test results.