Study On Axial Compression Behavior Of Concrete-filled Stainless Steel Tube Columns With Inner Distributed Seawater And Sea Sand Concrete-filled FRP Tubes

Nowadays,the demand for river water and river sand resources is increasing,and the use of seawater and sea sand can alleviate the shortage of river water and river sand.Concrete-filled steel tube is widely used in civil engineering field because it combines the characteristics of concrete and steel with superior mechanical properties.Stainless steel has the characteristics of corrosion resistance and good ductility,which can effectively avoid the erosion of chloride ions in seawater and sea sand concrete;FRP is also not corroded by seawater and sea sand concrete,and effectively restrains the concrete to improve the load-bearing capacity.Considering the characteristics of stainless steel and FRP,in order to apply seawater and sea sand concrete to engineering practice,this paper proposes a concrete-filled stainless steel tube columns with inner distributed seawater and sea sand concrete-filled FRP tubes,which is composed of three materials: external stainless steel tube,inner FRP tube and seawater and sea sand concrete.36 concrete-filled stainless steel tube columns with inner distributed seawater and sea sand concrete-filled FRP tubes and 4 stainless steel tube constrained seawater and sea sand concrete column comparison specimens with height and outer diameter of 477 mm and 159 mm were designed and fabricated,and the variation parameters tested were the thickness of stainless steel tube(4.5 mm and 6.0 mm),the diameter of FRP tube(75 mm,90 mm and 110 mm)and the number of FRP tube layers(2,3 and 4 layers).Monotonic axial compression experiments were conducted on the stainless steel tube seawater and sea sand concrete concrete composite columns with built-in FRP tubes,and the ultimate strength,ultimate strain and ultimate stress of each specimen were obtained.The loaddisplacement curves and stress-strain curves were also plotted based on the results.The test results showed that the relationship curve of the concrete-filled stainless steel tube columns with inner distributed seawater and sea sand concrete-filled FRP tubes was divided into four stages: elastic stage,yielding stage,strengthening stage and residual stage.In the elastic stage,the curve is linear growth and slope is larger,and the transverse strain is smaller than the longitudinal strain under the same stress value;in the yield stage,the slope of the curve decreases,the load growth rate decreases and the strain increases faster;in the strengthening stage,the curve continues to grow linearly and the slope is lower,until the FRP tube is destroyed and the load reaches the limit,the curve plummets and enters the residual stage,at which time,because the stainless steel tube has a better Ductility,excellent plastic deformation capacity,the specimen stress basically remains stable.When the thickness of the stainless steel tube increases,the bearing capacity and ductility of the stainless steel tube seawater and sea sand concrete combination column with built-in FRP tube is higher;when the number of FRP layers increases,the bearing capacity and ductility of the stainless steel tube seawater and sea sand concrete combination column with built-in FRP tube is higher;when the diameter of FRP tube increases,the bearing capacity and ductility of the stainless steel tube seawater and sea sand concrete combination column with built-in FRP tube is higher.Finally,the theoretical models of other scholars are collected,the accuracy of the test data in this paper is evaluated and analyzed,the lateral restraint of stainless steel tube and FRP tube on seawater and sea sand concrete concrete is considered,and the theoretical load-bearing capacity calculation model of stainless steel tube seawater and sea sand concrete concrete combined column with built-in FRP tube is proposed in accordance with this paper.The calculated values of the model were compared with the experimental values,and the results showed good agreement of the data,which provided the theoretical support for the subsequent more in-depth study and laid the foundation for the application in practical engineering.