Dynamical Response Of Steel Frame Structure Rapidly Cooled By Spray Water

With the development of national economy in China, steel structure has gradually become the main mode in building, but due to its poor fire resistance, steel structure could bring many potential risks in practical use. By now, many scholars begin to focus on their change situation of local and overall deformation and internal force for steel structure in cooling.Here, we use a transient thermal & mechanical coupling method, which is based on finite element analysis software ABAQUS, simulate on a single-layer and single-span and a three-layer and three-span steel frame structure. When the heating rate is the same but the cooling rate is different, we obtain the thermal & mechanical coupling changes of deformation and internal force under rapid cooling and natural cooling, which can help us analyze the dynamic response of the steel structure in heating and cooling.The largest difference between a single-layer and single span and a three-layer and three-span steel frame is their restraints between parts of component. The former restraint is less, so its deformation is much obvious, but the axial constraint has a large effect on the latter column deflection. Meanwhile, the rising and drop rate of the axial force at beam end are restrained by the rapid cooling, which can cause great influence on a practical steel structure in fire-fighting. The dynamic response of single-layer and single-span steel structure at different cooling rate is similar as that of three-layer three-span steel structure at its top layer room. The deflection and displacement of columns have a sudden change at a critical temperature under rapid cooling rate. In the three-layer three-span steel frame,the axial displacement in the middle room keeps a downward trend during the later heating.Moreover, the axial displacement decreases faster.For a single-layer and single-span steel structure, its axial force at beam end rapidly increases in rapid cooling, and it will never recover. At the later cooling, the dramatic changes of axial force at beam ends will also have an impact on the axial force at the adjacent beam ends. The closer the distance between fired beam and normal beam is, the larger the affection is. The bending moment at beam ends rapidly decreases due to the sudden increase of axial force, and it never recovers after cooling. The rapid increase of axial force and bending moment make beam weak at its ends, which has a negative effect on the stability of steel structure.In rapid cooling, the change rate of axial force and bending moment at top end of column increases, but it decreases slowly at first and then rapidly increases in naturalcooling. For a three-layer three-span steel frame, the axial force at top end of column in the top room has a sudden change at the critical temperature in rapid cooling, which will aggravate the destroy of losing stability for the columns in fire fighting.I hope that the research results can provide a useful reference on the fire resistance design of steel structure.