Fire Performance Of Concrete Filled Fire-resistant Steel Tubular Columns And The Stability Of Roof Purlin

In recent decades, the domestic scholars studied on the fire performance of concrete filled steel tubular column by experimental investigation and theoretical analysis. And the steel were usually ordinary steel. Many scholars also analyzed the fire resistance of fire-resistant(FR) steel members. Fire performance of concrete-filled steel tube(CFT) of FR steel have been little studied. To take advantage of merits of FR steel and concrete, this paper analyzed the fire performance of CFT of FR.Firstly, the temperature field of CFT of ordinary steel under the fire heating curves was simulated using ANSYS and analyzed under numerical parameters. The fire resistance and load-bearing capacity of CFT of FR steel were solved with numerical technique under different diameters, slenderness ratio, steel ratio, steel strength, concrete strength, exposure time, load eccentricity ratio and load ratio. The simplified calculation formula for predicting the fire resistance time and bearing capacity was deduced, which is found to be in good agreement with numerical results. The calculation formula may be referenced for the fire protection design of practical engineering. Parametric analyses show that the fire resistance time and bearing capacity of CFT of FR steel increase significantly in a certain period of exposure time compared with CFT of ordinary steel. Therefore, the thickness of fire-proof coating can be decreased.When fire retardant coating, cement mortar and autoclaved aerated concrete slabs are used as fire protection for CFT of FR steel under different parameters, the fire protection thickness were solved with numerical technique after temperature field of CFT obtained by ANSYS. The simplified calculation formula for predicting the thickness were deduced. Parametric analyses show that fire protection thickness of CFT of fire-resistant steel decrease significantly compared with CFT of ordinary steel. Therefore, the building space is saved.The influence of some parameters on the fire resistance, load-bearing capacity coefficient and fire protection thickness of concrete-filled flat tube of ordinary steel was analyzed. Compared flat column with equal-area and equal-perimeter column, the fire resistance and load-bearing capacity coefficient of flat column is smaller and fire protection thickness is much bigger. Flat column is used to reduce the occupied space. However, the fire protection thickness is too big to reach the goal. Then fire-retardant coating thickness was analyzed after replacing ordinary steel with FR steel.Three CFT of FR steel and one CFT of ordinary steel subjected to axial loads under standard fire curve (ISO-834) had been experimentally investigated. The experiment is to analyze the improvement of fire performance of CFT after replacing ordinary steel with FR steel and how the thickness of fire protection influence the fire performance of CFT of FR steel. The experimental results showed that the fire resistance time was nearly doubled. Therefore, the fire performance of CFT of FR steel was much better than that of CFT of ordinary steel with same protection.Fire performance of CFT of FR steel is the main content in this paper. The other content is the flexural-torsional buckling of purlins whose lateral restraints was ignored and torsional restraint was considered. The second content includes the following two aspects.An experiment mainly about 28 groups of profiled corrugated steel sheets is introduced. By changing thickness of roofing board, thickness of purlin, height of purlin web and shape of clips for standing seam roof panel, the total torsional restraint and factors that affect the total torsional rigidity were obtained. The torsional rigidity offered by roofing board, clip and purlin were solved separately with ANSYS, which were in good agreement with experimental results. The formulae for calculating the torsional rigidity of roofing board, clip and purlin were deduced. It is confirmed that total torsional rigid is formed by connecting three kinds of rigidity in series. Both test results and finite element analysis results show that the thickness of purlin is the most important factor which influences the torsional restraint.Based on the buckling theory of thin-walled members and the total potentials of cold-formed C and Z purlins whose lateral restraints was ignored, the formulae of rotation and lateral displacement of the purlins were obtained under wind suction on the principle of variation. Considering the nonlinear strain energy generated during flexural-torsional buckling by the stress before buckling, the expression of critical moment of C and Z purlins was obtained on the basis of stationary value of total potential energy. The rotation, lateral displacement and buckling moment were compared with numerical results using shell elements of ANSYS and found to be in excellent agreement with ANSYS.