Study On Fire Resistance Performance Of Double C-shaped Cold-formed Steel Section Column

Cold-formed steel composite structure with its high strength,lightweight,environmental protection and other advantages,has been widely used at home and abroad,with the national vigorous promotion of light steel structure system of residential and "rural revitalization" strategy implementation,cold-formed steel is widely used in low-rise industry,residential buildings.Although the current demand for cold-formed steel in China is increasing day by day,due to the relatively late research on cold-working steel in China,especially in recent years,frequent construction fires in daily life have caused huge losses to life and property,and the increasing number of cold-formed steel buildings has aroused the widespread attention of scholars to the fire resistance of cold-formed steel.In this thesis,the fire resistance of double-C-shaped cold-formed steel split section columns is studied,the effects of single parameter changes in axial compression ratio,length and slenderness ratio and bending amplitude on the fire resistance of double-C flattened cold-formed steel columns are studied,and the coupling parameters of axial compression ratio and length slenderness ratio are analyzed for the fire resistance of cold-formed thin-walled steel columns in the three fire states of single-sided fire,three-sided fire and four-sided fire,and the influence of multi-parameter coupling on the fire resistance of cold-formed steel columns under different fire conditions is analyzed.The analysis results show that:(1)the critical temperature of the steel column decreases significantly with the increase of the axial compression ratio;(2)The influence of the slenderness ratio on the critical temperature of the steel column is relatively small;(3)When unevenly subjected to fire,the influence of axial pressure ratio and length and slenderness comparison on the critical temperature of the component is relatively small,and with the increase of axial pressure ratio and length and slenderness ratio,the change of critical temperature becomes more and more significant;(4)The failure mode of the uneven fire steel column is different from its failure mode in the uniform fire state,and the failure of the uneven fire steel column is mainly controlled by the additional bending moment generated by the axial force caused by the uneven expansion,and the uniform fire state is caused by the change of the performance of the material itself under the action of high temperature caused by the failure of the component;(5)In the state of uneven fire,the component is more likely to cause the failure of the component than the uniform fire.In this thesis,the corresponding numerical analysis of the fire resistance of the refractory gypsum board protection steel column is carried out,the thickness of the refractory gypsum board is selected as the parameter,the temperature field effect of different thicknesses of refractory gypsum board is analyzed,and the fire resistance limit of the steel column of different thickness refractory gypsum board protection steel column is calculated.The analysis results show that:(1)the use of refractory gypsum board to protect the steel column can effectively improve the fire resistance limit of the steel column;(2)Although the thickness of the fireproof material cannot increase the critical temperature of the steel column,it can improve the fire resistance limit of the steel column by slowing down the heating rate of the steel column.On the basis of the numerical calculation results,the critical temperature data of the doubleC-shaped cold-formed steel flattened section column under different axial compression ratios and length-slender ratios were regressed to obtain the simplified calculation formula of the critical temperature,and the calculation formula of the temperature change with time was obtained by fitting the heating curve of the steel column protected by refractory gypsum board,and the calculation formula of the fire resistance limit of the refractory gypsum board was derived.On this basis,the commonly used fireproof plates(glass magnesium plate,calcium silicate board,CCA board)were selected to simulate the transient heat transfer numerical of the cold-formed steel columns protected by four commonly used fireproof plates,and the heating curves of the steel columns protected by different fireproof building materials were obtained,and the data were fitted and analyzed by SPSS data analysis software,and the heating calculation formula of four different fireproof building materials protected steel columns was obtained,which provided a reference basis for the fireproof design of flattened cold-formed steel columns.The market price of four fireproof panels was investigated,considering the fire resistance and cost economy of the components,the construction convenience and cost economy of fireproof gypsum board were better than those of the other three types of fireproof panels,but because of its fire resistance,it mainly determined its thickness.Therefore,for the three-and fourth-level refractory design requirements,the selection of gypsum board has a high cost performance;For the first and second level refractory design requirements,the choice of calcium silicate board is more advantageous.