Influence of actual plastic hinge placement on the behavior of ductile frames

The ultimate load and collapsing modes of steel frames under combined vertical and horizontal forces are investigated through finite element (FE) modelling and limit analysis. Consideration is given to a frequently overlooked problem which is the kinematics arising from the actual rotation of the plastic hinges under axial force and bending moment. This fact draws attention to the necessity of a careful assessment of the limit analysis approaches, a fact that might be seen as somewhat in line with the outcome from famous paradoxes, such as the one by Stüssi and Kollbrunner (1935), which can only be solved by making reference to both elastic and plastic deformations. As a result, it can be shown that in such a manner, it is possible to obtain a handy tool capable of competing with much more computationally expensive methodologies. The approach may be relevant to practising engineers dealing with code prescriptions and standardization committees.概要研究目的通过有限元分析和极限分析, 研究了在纵向和横向载荷下钢框架的最大负荷和坍塌模式, 并考虑了塑性铰链在轴向力和弯曲力矩的作用下在实际旋转时的运动学。研究方法在垂直和水平方向载荷共存的情况下, 基于轴向力和弯曲力矩的交互作用, 研究延性框架的极限载荷和坍塌模式对产生于塑性铰链的真实运动学的敏感性。 通过两个基本的案例和通过成功地评估非线性有限元分析和直接实施的极限分析步骤, 并利用 MATHEMATICA®, 揭示了其敏感性。重要结论在标准规程的框架下, 即使在最简单的案例中, 极限分析的主要结果也会考虑在坍塌时的运动学, 这与设计和加固的目的都是相关的。 如果没有对所有的结构元件的轴向力和弯曲力矩的交互作用进行合理的计算, 塑性铰链的定位计算可能得出不正确的坍塌机理和误导性的安全系数。 就具体方面而言, 本文清楚地表明, 在设计新的结构或者为现有结构进行加固时, 即使是使用看起来已经非常完备的经典步骤, 也必须非常小心。 本文的模型可以为处理规程设计的执业工程师和标准化委员会提供参考。