Effects Of Temperature Gradients And External Bending Moments On Restrained Steel Columns In Fire

Because of the special material properties of lightweight and high-strength, steel structure buildings emerge in response to the needs of times, and nowadays they have been extensively applied. But the poor fire resistance of steel structure buildings is unneglectable, the fire effects the mechanical properties of them and makes the resistance decrease, damage will be induced finally. The fire resistance of steel structure buildings is needed to be understood deeply due to the adverse effects of the fire on them, in order that the safety in fire can be ensured.Steel columns are the very important vertical and mechanical members and effect the resistance of the whole structure. When the steel columns destroy, the whole structure maybe collapse. So the security of steel columns in fire is very needed to research. We need use the spring to replace the boundary restraint action of surrounding members to analysis the behavior of restrained steel columns under the fire load.The nonlinear finite element program ABAQUS is adopted to analysis the fire resistance of restrained steel columns. Considering the flexural of the strong axis and initial imperfection, the analysis contents and innovative points mainly include the following three respects:(1) Parameters are studied on the buckling behavior of the restrained steel columns under uniform temperature distribution and axial load:the effects of initial imperfection, slenderness ratio, external axial load utilisation factor, axial restraint and rotational restraint on the mechanics performances and deformation performances of restrained steel columns in fire conditions. The results clearly show that initial imperfection, slenderness ratio, external axial load utilisation factor and axial restraint have the adverse effects on the fire resistance of restrained steel columns, but rotational restraint makes the fire resistance increase.(2) Parameters are studied on the buckling behavior of the restrained steel columns under non-uniform temperature distribution and axial load:the effects of temperature gradients on the mechanics performances and deformation performances of axial restrained steel columns in fire conditions. The results clearly show that the average critical temperature will reduce with the obvious temperature gradients.(3) The effects of external bending moments on the fire resistance of restrained steel columns under axial load and external moments are mainly studied.3D diagrams on the relationship of axial and rotational restraint stiffness and the critical temperature are first proposed, which establish the concept of safety zone and unsafe zone. The results clearly show that external bending moments have the adverse effects on the fire resistance of restrained steel columns.