An investigation of overturning moments of portal frames at elevated temperatures
An investigation of overturning moments of portal frames at elevated temperatures
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发表时间：
2009
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通讯作者：
Mahbubur Rahman;James B. P. Lim;R. Hamilton;T. Comlekci;D. Pritchard;Yixiang Xu
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作者：
Mahbubur Rahman;James B. P. Lim;R. Hamilton;T. Comlekci;D. Pritchard;Yixiang Xu
在英国，单层钢结构建筑占建筑钢结构的一半以上，这是由于其易于制造和成本效益。其中最常见的是门式框架。建筑钢材的主要缺点之一是对火灾的敏感性，因为钢材的强度和刚度会迅速下降。出于这个原因，通常需要防火，这会增加结构的费用。在火灾中，椽子往往会通过一个快速通过屈曲机制失去稳定性（见图1）。然而，当屋顶倒置时，这能够在高挠度下重新稳定。在静态分析方法中，只能确定初始稳定性损失。在火灾情况下，必须使边界墙保持接近垂直，以便不允许火灾蔓延到相邻的财产。由钢结构协会（SCI）提供的现行英国防火设计指南（参考文献1）提供了一种确定柱脚处倾覆力矩的方法，该倾覆力矩必须抵抗，以防止墙的稳定性。然而，该方法作出了一些任意的假设，并没有试图模拟火灾期间框架的真实行为。
In the UK, single-storey steel buildings account for over half of the constructional steelwork due to its ease of fabrication and cost-efficiency. The most common of these are portal frames. One of the major disadvantages of constructional steel is its sensitivity to fire, as steel looses strength and stiffness rapidly. For this reason, fire protection is often required, which can add to the expense of structure. In fire, the rafter often loses stability through a snap-through-buckling mechanism (see Fig. 1.). This, however, can be capable of restabilising at high deflections, when the roof has inverted. In static analysis methods, only the initial loss of stability can be determined. In fire conditions it is imperative that boundary walls stay close to vertical, so that fire is not allowed to spread to adjacent property. The current UK fire design guide (Ref.1) provided by Steel Construction Institute (SCI) provides a method for the determination of the overturning moment at the column base that must be resisted in order to prevent stability of walls. However, the method makes a number of arbitrary assumptions and does not attempt to model the true behaviour of the frame during fire.