Research On Axial Compression Performance Of Spirally Reinforced Seawater Sea Sand Concrete Filled Stainless Steel Tube Columns

Seawater sea sand concrete-filled stainless steel tube columns have great potential application value in marine engineering.However,the high price of stainless steel greatly limits the promotion and application of this type of composite column in ocean engineering.To this end,this paper innovatively proposes a spirally reinforced seawater sea sand concrete filled stainless steel tube column.The internal spiral bar can take into account the improvement of bearing capacity and deformation performance,so as to effectively reduce the amount of stainless steel tube.At the same time,the external stainless steel tube can not only resist the ocean corrosion environment,but also form a closed confinement space to block the corrosion reaction of the internal chloride ions to the steel cage.This kind of composite column has the advantage of corrosion resistance,good bearing capacity,considerable economy,beautiful and environmental protection,which has good application prospects in marine engineering construction in China.Based on the above,the axial compression performance of spirally reinforced seawater sea sand concrete filled stainless steel tube column is deeply studied by means of experimental research,numerical simulation and theoretical analysis in this paper.The main work and conclusion are as follows:（1）In this paper,the axial compression experiment of spirally reinforced seawater sea sand concrete filled stainless steel tube columns was carried out on 51 specimens.Variables included the presence or absence of reinforcement,the ratio of spiral bar content to longitudinal reinforcement content r_hv(r_hv=ρ_h/ρ_v),the diameter and spacing of spiral bars,and the diameter and number of longitudinal reinforcement.The mechanical failure process of the specimen was recorded,the load-displacement curve and steel strain-displacement curve were obtained,and the mechanical mechanism such as the mechanical characteristics,component yield sequence and deformation coordination performance of the specimen was explored.In addition,the influence of variables on the axial compression performance of specimens was discussed from the aspects of ultimate bearing capacity,axial ductility,energy absorption capacity and damage development.（2）The results showed that this composite column had good deformation coordination performance.The built-in steel cage can effectively improve the bearing capacity,deformation performance and energy absorption performance of the composite column.In addition,the development of specimen damage was effectively inhibited.Under the same content of reinforcement,the axial compression performance of specimens was the best when the r_hv=0.88.And the effect of adjusting the configuration mode of spiral bar on the specimen’s axial compression performance was greater than that of adjusting longitudinal reinforcement.On the other hand,with the increase of spiral bar spacing（diameter increase）,the ultimate bearing capacity,ductility and energy dissipation of specimens showed decreased.（3）Based on the test results,a refined finite element model was developed in this paper.Which can accurately predict the load-displacement curve,failure pattern,stress process and other macroscopic mechanical characteristics of spirally reinforced seawater sea sand concrete filled stainless steel tube columns under axial compression.In addition,80 specimen examples were completed based on the verified finite element model.And the parameters such as stainless steel tube wall thickness,concrete cube compressive strength,stainless steel yield strength,spiral reinforcement yield strength,longitudinal reinforcement yield strength,spiral bar volume ratio and so on were expanded and analyzed.The numerical simulation results showed that the wall thickness of stainless steel pipe,the yield strength of stainless steel tube,the volume stirrup ratio of spiral bar and the strength of concrete had significant effects on the axial compression capacity.Under the condition of increasing the same amount of steel,increasing the amount of spiral bar had the highest efficiency in improving the axial compression bearing capacity,followed by stainless steel,and the longitudinal reinforcement is the smallest.（4）A method for calculating the ultimate bearing capacity of spirally reinforced seawater sea sand concrete filled stainless steel tube columns under axial compression was proposed by considering the superposition of constraint effects.At the same time,the calculation method proposed in this paper was compared with the method proposed in other literatures.It was verified that the calculation formula proposed in this paper has better accuracy and smaller dispersion.The results of this paper revealed the failure mechanism of spirally reinforced seawater sea sand concrete filled stainless steel tube column under axial compression.And put forward the calculation method of ultimate bearing capacity and configuration suggestions of this kind of composite column.Which enriched the application theory of stainless steel tube concrete structure in offshore and marine engineering,and laid the foundation for subsequent research.