Test and Bearing Capacity Calculation Method of Concrete-Filled CFRP-Stainless Steel Sandwich Tube Columns Under Axial Compression

In order to enhance the bearing capacity and durability of thin-walled stainless steel structures, a kind of seawater sea sand concrete-filled CFRP-stainless steel sandwich tube structure, that is, in which the inner and outer walls of stainless steel tube were pasted with CFRP (Carbon Fiber-Reinforced Polymer) composite constrained seawater sea sand concrete, was designed. Then, monotonic static axial compression tests were carried out on 18 short column specimens, with the number of pasting layers and pasting methods of CFRP as the variation parameters. The failure process and morphology of the specimens were observed, the load-displacement curves and material strain distribution data were obtained, and the variation law of the axial compression mechanical properties of the specimens was analyzed. The results show that: (1) the internal and external CFRP can effectively improve the bearing capacity and deformation capacity of the structure; (2) the failure modes of the specimens without CFRP and the specimens with internal CFRP are both shear damage, but the shear damage will change to waist drum damage with the increase of the number of external CFRP layers; (3) with the same pasting methods, the bearing capacity, deformation capacity and energy dissipation capacity of the specimens increase non-linearly with the increase of the number of CFRP layers; and (4) with the same pasting layers, the mechanical properties of the specimens with internal CFRP are better than those with external CFRP,and the ultimate bearing capacity of the specimen with one or two internal CFRP layer respectively increases by 5.6% or 6.7%, as compared with that of the specimen with external CFRP, and the energy dissipation capacity of the specimen with one internal CFRP layer is equivalent to that of the specimen with two external CFRP layers. Moreover, the strain analysis results show that CFRP and stainless steel have good cooperative performance before the specimen is damaged. Finally, based on the limit equilibrium method and by considering the strain hardening effect of stainless steel, a formula for calculating the ultimate axial compressive bearing capacity was proposed and 73 sample data were collected for verification, finding that the calculated values accord well with the test ones.