Finite Element Analysis Of Fire Performance Of Concrete-filled Double Skin Tubular Columns With External Stainless Steel Tubes

The concrete-filled double skin tubular column with external stainless steel tube is a new kind of composite structure formed by replac ing the outer steel tube in the concrete filled double skin tubular composite structures with stainless steel tube.Such members have advantages of unfolding cross-section,high flexural stiffness,light weight,high bearing capacity,good fire and corrosion resistance,so they are especially suitable for the(super)high-rise buildings,industrial plants and other projects which require high stability,high temperature and corrosion resistance.At present,there have been systematic studies on the mechanical properties of the concrete-filled double skin tubular composite structures and concrete filled stainless steel tubular columns at room and elevated temperatures,the mechanical properties of the concrete-filled double skin tubular columns with external stainless steel tubes at room temperature have also been reported.However,few studies have been reported on the mechanical properties of the concrete-filled double skin tubular columns with external stainless steel tubes at elevated temperatures.Therefore,this paper will study the fire performance of the circular concrete-filled double skin tubular columns with external stainless steel tubes.The main research contents and results are as follows:(1)Four different finite element models were developed,i.e.,1)slender concrete-filled stainless steel tubular columns under axial compression,2)fire performance of concrete filled steel tubular columns,3)fire performance of self-consolidating concrete filled double skin steel tubular columns,4)fire performance of concrete filled stainless steel tubular columns.The predicted axial force and mid-span displacement at room temperature and axial deformation-time at elevated temperatures curves were compared with the experimental results to indirectly verify the reliability of finite element analys is model of the concrete-filled double skin tubular columns with external stainless steel tubes.`(2)By us ing the method of sequentially-coupled thermal-stress and the verified finite element analysis model,typical samples were selected to analyze their mechanism.Ultimate bearing capacity at room temperature,temperature distribution,failure mode and the axial deformation-time relationship,as well as stress and strain of inner steel tube,outer steel tube and concrete were analyzed.The results showed that the concrete-filled double skin tubular columns with external stainless steel tubes presented good fire resistance,and its failure modes at elevated temperatures were overall buckling model;when the hollow ratio and the axial load was small,the second expansion stage appeared in the axial deformation-time curves.(3)Based on mastering the fire res istance mechanism of the concrete-filled double skin tubular columns with external stainless steel tubes,the parameters affecting their fire resistance were analyzed for 144 times.The parameters were: hollow ratio,load ratio,load eccentric ity,yield strength of inner steel tube and concrete strength.The results showed that the hollow ratio,load ratio and load eccentric ity have great effects on the fire resistance of this composite member.Within the range of parameter analys is in this paper,the fire res istance of samples increases with the increase of the hollow ratio;when the hollow ratio is small,the concrete strength has a large effect on the fire resistance of the samples;when the hollow ratio is large,the yield strength of the inner steel tube has a great effect on the fire resistance of the samples.(4)Based on the results of parametric analysis,some suggestions were proposed for the fire resistance design of the concrete-filled double skin tubular columns with external stainless steel tubes inc luding fire protection material thickness,material strength selection and production process.