Performance Of Concrete-Filled Steel Tubular (CFST) Members Subjected To Combined Compression (Tension)-Bending And Chloride Corrosion

When concrete-filled steel tubular(CFST)members serve in marine or offshore structures,they may suffer the combined effects of chloride corrosion and sustained load.It is a critical issue for practice while previous resear ch on this is yet limited.This dissertation thus investigates the full-range mechanism,the typical failure modes,the ultimate states in terms of strength and the design methodology for circular and square CFST members subjected to combined compression(tension)-bending with consideration of chloride corrosion,sustained load,etc.The main research work and the achievements obtained include:1.Finite element analysis(FEA)modelling for the full-range simulation of CFST members subjected to combined comp ression(tension)-bending is established,with the chloride corrosion,the sustained load,the initial imperfection(caused by cold-forming or welding of the steel tube)and the preload during construction taken into consideration.A series of experiments on CFST tensile members and beam-columns under combined chloride corrosion and sustained load are conducted,while the effects of key parameters are studied,e.g.,the corrosion depth of steel tube and the long-term load ratio.Feasibility of the established FEA modelling is verified based on experimental results.2.Based on the validated FEA model,the influence of chloride corrosion and other important factors on the full-range load-displacement relationship,the failure mode,the load-transfer mechanism and the composite effect in CFST members subjected to combined compression(tension)-bending are revealed.The mechanism of ultimate states are studied.Meanwhile,the change in strength correlation curves,the effects of various loading paths as well as the shear effects are discussed.3.Systematic parametric studies on the performance of CFST members subjected to combined compression(tension)-bending and chloride corrosion are carried out,with the bearing capacity ultimate states considering chloride corrosion and other factors defined.The studied parameters include the material strengths,the steel ratio,the slenderness ratio,the load eccentricity ratio,the long-term load ratio,the preload ratio and the degree of corrosion.Based on the parametric analysis,practical design methods for the bearing capacity of CFST members subjected to combined compression(tension)-bending and chloride corrosion are suggested.The proposed methods are verified with the test results.4.A database containing the reported test data of 2,674 CFST specimens is established.Based on the database,reliability analysis and evaluation is conducted by using the first-order second-moment(FOSM)method(central point method).The results show that in the parametric range of this dissertation,the reliability indexes β for both circular and square CFST members subjected to combined compression(tension)-bending and chloride corrosion are greater than 3.2 if designed with the proposed method,which meets the corresponding requirements for structures with second safety level according to Chinese code GB 50068.Based on the reliability analysis,the partial factors for the axial compressive(tensile)strength of CFST are suggested.