Research On Fire Resistance Of Cross-shaped Steel Pipe Columns Protected By Intumescent Fireproof Coating

In recent years,steel structure building develops rapidly and is widely used in various large buildings.Steel structure itself has many advantages,but its fire resistance is poor,resulting in frequent fire.Therefore,the fire protection design and fire analysis of steel structure is very necessary.In order to prevent fire in steel structure building,fire retardant coating is often used as a fire protection measure of steel structure.The cross-shaped steel pipe column of a large railway station in Beijing is of grade 1 fire resistance,which should meet the requirement of3.00 h fire resistance limit.Non-expansion fire retardant coating can generally provide more than 3.00 h fire protection for steel structure column,but its since heavy,easy to fall off,difficult to construct,not beautiful and subsequent maintenance is difficult,so the expansion type fire retardant coating is selected as the fire protection measures of cross steel pipe column.In the current specification for steel members that need to meet the 3.00 h fire resistance limit,generally do not choose expansion type fire retardant coating.In the study of fire resistance of engineering structures,due to the limited cost and equipment,scale models are often used instead of full size specimens to carry out fire resistance tests.To verify the expansion type fire retardant coatings can provide cross steel tube column with 3 h fire protection,lie in the high temperature in the furnace of 12 elements of the expansion type fire-retardant coating protection cross-shaped steel tube column scale model to carry out the fire test,with different cross section forms,different film thickness for parameters,to study the temperature field distribution and the curve of temperature rise and expansion type fire retardant coating failure pattern,status,attached.At the same time,based on the parameters of full-size components in practical engineering,the finite element model is established for theoretical calculation,which mainly includes :(1)the heat transfer model is established to calculate the temperature field of full-size cross-shaped steel pipe without fire protection and with fire protection.(2)According to the load effect of the column in the actual project,the thermal coupling analysis of the cross steel pipe column protected by the expansion type fireproof coating under the action of the adverse load combination in the actual project is simulated,and the fire resistance limit of the full size member is calculated.(3)The thermodynamic coupling analysis of the cross steel pipe protected by the expansion type fireproof coating under different axial force load ratios and eccentricities was calculated to obtain the relationship between the axial displacement of the column and the change of load ratio,and the maximum axial force and the corresponding load ratio were calculated on the premise of meeting the 3.00 h fire resistance limit requirements.Through the combination of experimental research and finite element analysis,the following conclusions are obtained :(1)the expansion type fireproof coating can provide3.00 h fire resistance limit protection for the cross-shaped steel pipe in practical engineering.(2)The average net film thickness of the expansion type fireproof coating should not be less than 4mm.(3)The full-length cruciform steel pipe column protected by expansive fireproof coating under uniaxial compression can meet the 3.00 h fire resistance limit when the axial load ratio is not greater than 0.66.The relationship between load ratio and axial displacement and the relationship between column load ratio and axial displacement at different eccentricities were fitted.