| Stainless steel is commonly used in marine engineering structures because of its excellent corrosion resistance and mechanical properties.Using seawater sea sand to make concrete can alleviate the excessive use of river sand,and at the same time,it can reduce the construction cost of offshore projects by taking local materials.However,the expansive cost of stainless steel is still the key factor which limits its extensive utilization.Carbon steel embedded concrete-filled stainless steel tubular columns can improve the steel content,reduce the size of the combined column cross-section and improve the load-bearing capacity of the member.In this paper,stainless steel,carbon steel(including square steel tube,circular steel tube,steel sections and spiral reinforcement)and marine concrete were combined.Based on the available experimence and the finete element analysis,this study aims to examine the behaviors of four types of carbon steel built-in MCFST columns,and on this basis,the calculation method of axial compression load capacity based on composite restraint is proposed,and the specific work and the related findings are as follows.1.A total of 10 specimens were tested under axial loads to examine the axial compressive behavior of marine concrete-filled stainless steel tubular(MCFST)columns with built-in carbon steel.The mechanical damage process and specimen morphology were observed,and the axial load-displacement curve and the strain curve of each steel were obtained.Based on the test data,the influence of various variation parameters on the ultimate bearing capacity,axial ductility,energy dissipation capacity and damage development of kinds of specimen was analyzed.The results showed that the built-in carbon steel effectively improved the axial compression performance.2.For four types of built-in carbon steel marine concrete filled stainless steel tubular columns,finite element model analysis was established and verified with the existing test results.A series of parametric analyses were carried out,and a total of 64 specimens were completed for the finite element analysis calculations.The confinement mechanism of the combined column with four cross-sectional forms is revealed,and the internal force contribution of each component,the confinement force between steel and concrete,and the stress distribution are studied.The effects of stainless steel strength,outer tube wall thickness,carbon steel strength,concrete strength,inner and outer tube diameter ratio(or width to diameter ratio)and other factors on the mechanical properties of the specimens were studied.The results show that bicircular cross-sectional forms are relatively better,subject to a more uniform distribution of constraints,and have better axial compression performance.3.Base on test and finite element analysis,considering the effect of the double constraints of stainless steel tube and carbon steel,the calculation methods of bearing capacity were proposed.Compared with the test value of this paper and the test data of related literature,and the calculated value reflected the measured data well.Finally,ultimate strength was compared and evaluated according to the Eurocode 4,AIJ,ACI and GB 50936. |
