Study On Axial Compressive Mechanical Properties Of High Performance Concrete Filled Square Hollow Sandwich High Strength Steel Tube Columns

As a new type of concrete filled steel tubular structure,hollow sandwich concrete filled steel tubular structure not only has the advantages of traditional concrete filled steel tubular structure,but also is widely used in bridge engineering,support column and other structures with its light weight,large bending stiffness,good seismic performance,good plasticity and good fire resistance.In order to meet the requirements of high bearing capacity,light weight and convenient construction of modern engineering structures,a square hollow sandwich high strength concrete filled steel tubular column is proposed in this paper.The ordinary steel pipes inside and outside the concrete filled steel tubular are replaced by Q460 high strength steel pipe,and the ordinary concrete in the sandwich is replaced by high performance concrete.The ultimate bearing capacity of square hollow sandwich concrete filled steel tubular is improved by strengthening the strength of steel pipe and improving the strength of core concrete.The mechanical tests of 42 high-performance concrete filled square hollow sandwich steel tube columns under axial compression were carried out,and the failure mode,load-deformation curve,load-strain curve and ductility coefficient of the specimens were analyzed.The consistency between the existing four formulas for calculating the ultimate bearing capacity of concrete-filled square hollow sandwich steel tube short columns and the test in this paper is discussed.The correction factors considering the wall thickness of internal steel tube,hollow ratio and length-diameter ratio are fitted by data analysis software,and the ultimate bearing capacity of high-performance concrete-filled square hollow sandwich steel tube short columns is calculated.Compared with the actual test value,it is found that the consistency is good,which provides a theoretical basis for engineering design and application.The main research work and conclusions of this paper are as follows.(1)Thirty-five square hollow sandwich high strength steel pipe high performance concrete columns(hereinafter referred to as DCFST-HPC)and seven square high strength steel pipe high performance concrete columns were fabricated with inner steel pipe wall thickness,hollow ratio and length-diameter ratio as the variation parameters,and axial compression mechanical performance tests were carried out on them,and the damage morphology,load-deformation curve and load-strain curve of the specimens were analysed.(2)The axial compression test results show that the ultimate bearing capacity of the specimen increases with the increase of the wall thickness of the inner steel tube within a certain range.With the increase of the hollow ratio,the ultimate bearing capacity of the specimen increases first and then decreases.When the hollow ratio of most specimens is 0.29,the ultimate bearing capacity of the specimen reaches the maximum.It is suggested that the optimum hollow ratio can be set near 0.29,and the DCFST-HPC middle-long column with hollow interlayer is better than the short column.With the increase of aspect ratio,the ultimate bearing capacity of specimens also shows different trends due to different hollow ratios.The change of ultimate bearing capacity of specimens with hollow ratio of 0.29 is not obvious.The ultimate bearing capacity of specimens with hollow ratio of 0.44 shows a slow downward trend.The decrease of ultimate bearing capacity of specimens with hollow ratio of 0.55 is significantly increased,and the decrease of ultimate bearing capacity of solid square high-strength steel tube high-performance concrete column is the largest.(3)Based on the calculation formula of the ultimate bearing capacity of the hollow sandwich concrete-filled steel tubular short column proposed by the existing domestic and foreign codes and experts,the ultimate bearing capacity of the DCFST-HPC column under axial compression is calculated,and the test results are compared and analyzed.On this basis,this paper uses the data analysis software to fit the calculation formula of the ultimate bearing capacity of the DCFST-HPC column under axial compression considering the three variables of the wall thickness of the internal steel tube,the hollow ratio and the slenderness ratio.