混凝土楼板在火灾下局部开裂破坏的有限元模拟

Finite Element Modelling of Localized Cracks in Reinforced Concrete Slabs at Elevated Temperatures

火灾中钢框架结构的混凝土楼板在高温下会发生大变形,导致楼板中存在非常显著的局部裂缝。这种局部裂缝会导致钢筋直接暴露在火中,削弱楼板的"膜效应",因此显著降低楼板乃至整体结构的耐火极限。鉴于此,采用扩展有限元方法来模拟楼板中的局部裂缝,编制了可同时预测楼板在火灾下的整体性能(变形和耐火极限)和局部破坏(局部裂缝开展)的非线性有限元程序。数值计算结果表明,本文的有限元程序可较好的预测火灾下局部裂缝在楼板中的开展并可有效预测其裂缝宽度,从而提供了一个可同时评估楼板整体抗火性能和局部开裂破坏的有效工具。

Under fire conditions, the concrete slab in steel frames can be forced into large deformation, resulting in the formation of large individual cracks within floor slabs. These localized cracks may expose steel reinforcement directly to fire and damage the membrane action of slab, thus significantly reducing the fire resistance of the buildings. This paper presents a robust finite element procedure for predicting both global response （deformation and fire resistance） and localized failure （localized individual cracks） of concrete slab at elevated temperatures, which uses extended finite element method to capture the localized cracks within reinforced concrete floor slabs. The new model has been validated against previous fire test results. It is evident that the nonlinear procedure proposed in this paper can effectively capture the propagation of individual cracks and predict the opening of cracks, thus providing engineers a tool for assessing both the global response and the integrity failure of the floor slabs in fire.