端弯矩与端部约束对钢柱抗火性能的影响

Effects of external bending moments and end restraint stiffness on the fire resistance of steel columns

基于有限元方法模拟约束钢柱在火荷载作用下的抗火行为,分析轴向约束刚度、转动约束刚度、同向曲率的端弯矩作用对其抗火性能的影响,探讨轴向约束刚度、转动约束刚度与临界温度之间的关系。通过对约束钢柱火灾下的受力及变形性能较为全面地进行参数分析,得出:轴向约束刚度比增大,钢柱临界温度降低;转动约束刚度比增大,临界温度升高;在轴向约束条件下,截面温度分布均匀时端弯矩作用使钢柱临界温度显著降低;截面温差为200℃时,端弯矩作用的不利影响更加明显,端弯矩作用越大,受约束钢柱抗火性能越低;具有转动约束的钢柱,约束作用较小时,端弯矩作用会对其抗火性能产生不利影响,约束作用较大时,端弯矩作用对其抗火性能影响较小;截面温差为200℃时,端弯矩作用下的转动约束钢柱临界温度值几乎与轴向荷载作用下相同。另外,划分了"安全区"和"非安全区"两个区域,在抗火设计中保证钢柱的温度在安全区范围内,钢柱的抗火能力即可满足要求;端弯矩作用对约束钢柱抗火性能具有不利影响,会使安全区范围缩小。

Nonlinear finite element numerical simulation is carried out to analyze the behavior of restrained steel columns under the fire load and main attention is focused on the effects of axial and rotational restraint stiffness and external moments on the fire resistance of restrained steel columns. More comprehensive parameters are studied on the mechanics performances and deformation performances of restrained steel columns in fire conditions. The more axial restraint stiffness is, the lower the critical temperature of steel column is, and the more rotational restraint stiffness is, the higher the critical temperature of steel column is. The safe zone and unsafe zone are established, and the fire resistance of restrained steel columns is well within the safe zone. Results obtained clearly show that external moments significantly reduce the critical temperature of axially steel columns, even the adverse effects of external moments on the cross-sectional non-uniform heating profile(200℃) is more obvious, and the critical temperature of axially steel columns is lower when external moments are larger. External moments have the adverse effects on the restrained steel columns with lower rotational restraint stiffness, but they have very limited effects on the fire resistance of the restrained steel columns with larger rotational restraint stiffness and the critical temperature is almost the same as steel columns under the axial load on the cross-sectional non-uniform heating profile(200℃). External moments have the adverse effects on the fire resistance of restrained steel columns, and the scope of the safe zone decreases.