Experimental Research On Short Columns Of Manufactured Sand Concrete Filled Steel Tubes

The Fifth Plenary Session of the 19 th Central Committee of the Party adheres to the new development concept,emphasizes green development,and promotes high-quality development.For a long time,natural river sand(RS)has been used as fine aggregate to make concrete.However,the over-exploitation of RS has also brought certain damage to the environment.Due to the requirements of sustainability,the supplement of RS is decreasing every year.To solve the problem of RS shortage.It is recommended to replace RS with manufactured sand(MS)produced by mechanically crushing original rocks or construction waste.However,it is reported that most MS concretes have higher strength but lower ductility.In order to promote the application of MS in concrete,considering the advantages and benefits of the composite structure,concrete-filled steel tube(CFST)columns are used to improve the overall ductility and bearing capacity of the composite structure.On the other hand,it is well known that wet packing density(WPD)will significantly affect the overall performance of concrete,but so far,there has been no research on the effect of WPD on the performance of concrete(such as concrete in CFST columns).Therefore,in this article,the research on the material properties of MS concrete and the mechanical properties of CFST columns under axial compression will be carried out,and the influence of concrete strength,MS replacement rate and steel tube diameter-thickness ratio on the bearing capacity of CFST columns will be explored.In order to study the material properties of MS concrete,this paper combines the working performance of fresh concrete,the mechanical properties of MS concrete,and the WPD of concrete.Research shows that MS has sharper edges and corners,rougher surface,and more holes than RS.Under low-strength concrete,the MS substitution rate has a certain influence on the strength of MS concrete.As the strength increases,WPD has a greater effect on the strength of MS concrete.The impact is reduced.In order to study the axial performance of the CFST column,a total of 35 CFST column specimens with MS partially or completely replaced RS were designed and tested under uniaxial compression.Experimental research shows that the performance of CFST specimens using MS concrete is similar to that of RS concrete.1.The failure mode shows that the CFST presents waist-drum type damage,with buckling in the middle part and local buckling of elephant foot type near the end.Summarized the three stages of CFST in the test process,namely the elastic stage,the elastoplastic stage and the plastic stage.2.The bearing capacity of CFST increases as the strength of concrete increases,and the growth rate of bearing capacity will slow down as the strength of concrete increases.3.Under low-strength concrete,the influence of MS substitution rate on bearing capacity is consistent with the trend of WPD.4.The reduction of the diameter-to-thickness ratio will increase the improvement of low-strength concrete more obviously,and the higher the strength of the core concrete,the improvement will be reduced.5.Under the same diameter-to-thickness ratio,the small-sized specimens show better rigidity.6.The greater the wall thickness of the steel pipe,the greater the ductility of the test piece.7.Compare with the current specifications,and design a derivation formula,which shows good agreement and accuracy,and is suitable for actual engineering.