Study On Post-fire Mechanical Behavior Of High Strength Q460 Steel Columns

Steel structures have been widely used in building structures because of the advantages of light weight, high strength and convenient construction, and have gradually become the preferred form in large span and high-rise structures. In recent years, the continuous innovation of large steel structure engineering requests of steel has higher strength, while meeting the needs of a larger building space, thus contributing to the development and application of high strength steel. Local fire does not generally cause fundamental damage to the structure. Demolition and reconstruction will result in a serious waste of resources. So we need to identify the bearing capacity of structure after fire.The residual bearing capacity of axial compression members of high strength Q460 steel after being exposed to fire were investigated experimentally and numerically in this research. The main contents and conclusions are as follows:(1) Material properties: 15 groups of a total of 45 specimens were designed, of which 42 specimens were heated treatment. Two cooling methods were considered, namely, natural cooling and water cooling. Tensile tests were performed on specimens after high temperature and 3 specimens at normal temperature were also tested as contrast. The strain-stress curves, yield strength, tension strength, elastic modulus and percentage elongation after fracture were obtained after different temperatures and different cooling methods. The mechanical properties of Q460 steel after high temperature were compared with that of mild Q235 steel and similar high strength S460 steel.(2) Theoretical analysis: The domestic and foreign calculation methods of axial compression bearing capacity of the overall stability at normal and high temperature were introduced, and the theoretical analysis method was extended to the calculation of residual bearing capacity after high temperatures.(3) Experimental study: Experimental investigations were carried out to clarify the residual bearing capacity of Q460 post-fire steel welded H section and box section members. The experiment was divided into two steps. Firstly, those specimens were exposed to fire in an unstressed condition. Temperature curve was in accordance with the ISO-834 standard temperature curve. Secondly, the axial compression test was conducted after cooling to ambient temperature. The load-deflection curves, load-axial displacement curve and load-angle curve after high temperature were obtained. Through the comparison of test results before and after fire and the a~c column curves in "code for design of steel structures"(GB50017-2003). A conclusion that the current adopted design curves can be extended to post-fire welded Q460 high strength steel columns was drawn.(4) Finite element analysis: The residual bearing capacity of Q460 post-fire steel was simulated by the finite element software ANSYS. Through the comparison between the simulated results and test results, the accuracy of the established model was verified.(5) Parametric analysis: The FE model was established, and the simulated result was validated by experimental result. Parametric analysis was carried out to calculate the residual bearing capacity of steel columns after fire, as an expansion of test results. An initial bending of 1/1000 of column length and simplified residual stress model were considered. The main parameters were heating temperatures, slenderness ratio and cooling methods. Then the residual bearing capacity of steel column simplified calculation method was proposed on the basis of parameter analysis.