火灾下蠕变对轴向约束钢柱屈曲的影响

目前,大多采用考虑蠕变的Harmathy蠕变模型进行耐火性分析。Harmathy蠕变模型仅能预测恒定应力下一定精度的蠕变,不适用于应力变化的情况。轴向约束钢柱遇到火灾时,火灾过程中应力将随着时间和温度的变化而迅速变化。该文研究了火灾下蠕变对轴向受压钢柱屈曲性能的影响。使用ANSYS软件中能够预测任何时间、应力或温度下钢材蠕变应力的蠕变模型来预测蠕变应力。分别对考虑和不考虑蠕变的情况进行数值模拟,并对两种情况下的屈曲温度和轴向变形结果进行对比分析。快火和慢火工况都考虑在内。研究结果显示,慢火工况下考虑蠕变的轴向约束钢柱屈曲温度高于不考虑蠕变的屈曲温度,快火工况下考虑蠕变的轴向约束钢柱屈曲温度可能高于也可能低于不考虑蠕变的屈曲温度。

Creep Effect on Buckling of Axially Restrained Steel Columns in Real Fires

At present, Harmathy creep model is used in most fire resistance analysis, which explicitly consider creep. Harmathy creep model only predicts creep strains with acceptable accuracy for the case of constant stresses, but becomes invalid for the case of variable stresses. For the case of axially restrained steel columns subjected to fire, the fire induced stresses vary considerably and rapidly with time and temperature. In this paper, the effect of creep on the buckling behavior of axially restrained steel columns in real fires has been investigated. A creep model in ANSYS, which is capable of predicting creep strain regardless of any coupling between time and either stress or temperature of steel, is used to predict creep strains. The results for buckling temperatures and axial deformations, predicted with and without considering creep in numerical simulations, are compared. Both fast and slow fires are considered. The study found that for axially restrained steel columns in slow fires, considering creep gives higher buckling temperatures than those not considering creep; and for axially restrained steel columns in fast fires, considering creep might give higher or lower buckling temperatures than those not considering creep.