Behaviour Of Axially Loaded Square Concrete Filled Steel Tubular Stub Columns With Local Corrosion Simulated By Mechanical Notch

Concrete filled steel tubular(CFST)columns are widely used in construction due to its numerous advantages,such as high strength and stiffness,good ductility and convenience in construction.However,as other metal structural elements,material imperfections always exist in the outer steel tube of the CFST members,which may impair their structural integrity and affect their service life.Such material imperfections are mainly due to the defects or thickness variations by the corrosion,welding or other chemical attacks.Despite its wide application,researches on the influence of such imperfections of steel material on the mechanical behavior of axially loaded CFST columns is insufficient,and there is no special method in the existing design codes that takes these imperfections into account.This thesis concerns with the influence of the mechanical notch in the outer steel tube on the behavior of the square CFST stub columns under the axial compressive loads.In this study,the notch in the outer steel tube was used to represent the material imperfection from local corrosion.The research study presents the combination of the experiments and finite element analysis to quantify the failure mechanism after the ultimate compressive loads and investigate the parameters that influence on the basic mechanical properties of the notched square CFST stub columns.The main content of this paper:1)Experiments were conducted on total of 19 notched square CFST stub columns to investigate their behavior under the axial compressive loads.The main parameters considered in this experimental study were the length,width,depth and orientation of the notch in the outer steel tube.The influence of these parameters on the failure modes,loaddeformation relationships and ultimate loads was analyzed.The experimental results showed that the notched square CFST stub columns have quite different failure modes from the intact ones.The typical failure modes of the notched specimens were the bulging,closing or local buckling of the notch in the steel tube depending on the notch orientation.By increasing the length of the horizontal and sloping notch,the ultimate bearing capacity of the columns was decreased due to the reduction of the effective section area of the steel component.The notch orientation also has a significant influence on the ultimate load.And finally,the length,depth and width of the vertical notch almost has no influence on the bearing capacity of the notched square CFST columns.2)The finite element(FE)models of the notched square CFST stub columns under the axial compression were developed by the commercial software Abaqus.The developed FE model was validated using experimental results from current study and reasonable agreement was reached between the experimental results and the predicted FE analysis results.The ultimate strength obtained from experimental and numerical analysis were identical.3)Further parametric analysis using the developed FE model was conducted to investigate the influence of the notch lengths,notch orientation,notch depth,steel yield stress,concrete compressive strength and steel ratio on the bearing capacity of the notched square CFST stub columns under the axial compressive loads.By increasing the length of the horizontal and sloping notch,the ultimate bearing capacity of the column was reduced.The length of the vertical notch had a minimal influence on the strength of the column.By changing the notch orientation from 0 to 90°,the bearing capacity of the square CFST stub column was improved,and the ductility was reduced.With the same horizontal component of the notch length,the notch orientation had a minimal effect on the ultimate strength of the columns.Increasing the depth of the horizontal notch led to a significant decrease in the effective area of the steel component,and therefore to a reduction in the carrying capacity of the square CFST stub columns.By increasing the yield strength of the outer steel tube,the ultimate bearing capacity of the notched square CFST stub column was improved for any notch orientation.By increasing the compressive strength of the concrete core the bearing capacity and stiffness were improved,but columns demonstrated brittle fracture.By increasing the steel ratio,the carrying section capacity,ductility and stiffness of the notched square CFST stub columns were improved,regardless of the notch orientation.4)Finally,a theoretical method for estimating the ultimate bearing capacity of the notched square CFST stub columns was proposed based on the change in the effective section area of the outer steel tube.The results calculated using the proposed method were the nearest to the experimental results and the FE analysis results.