The introduction and the influence of semi-rigid connections in framed structures subjected to fire

This paper describes a recent development in a finite element software dedicated to the modeling of structures in fire which deals with the way connections are simulated in global structure analyses. This development allows modeling semi-rigid, temperature-dependent connections between beam-type finite elements. It relies on the definition of additional internal degrees of freedom in the elements. The objective is to enable efficient analysis of the influence of semi-rigid connections on the global structural response and on the demands for these connections. The theory and implementation are described in a geometrically non-linear software with large displacements. Then, a 3D frame structure is analyzed as a case study. The analyses show that structural capacity and failure mode depend on the degree of rotational restraint at the beam-column connections and at the base of the columns. The maximum fire resistance is obtained for an intermediate degree of restraint between beams and columns, while higher restraints lead to an unfavorable sway failure mode. The case study illustrates the capabilities introduced by the new development, and demonstrates that the effects of the connections on global response is complex, justifying the need for practical numerical methods for design and parametric analyses of structures in fire.

本文介绍了一种用于火灾中结构建模的有限元软件的最新进展，该进展涉及在整体结构分析中模拟连接的方式。这一进展允许对梁式有限元之间的半刚性、温度相关的连接进行建模。它依赖于在单元中定义额外的内部自由度。其目的是能够有效分析半刚性连接对整体结构响应以及对这些连接需求的影响。在一个具有大位移的几何非线性软件中描述了相关理论和实现。然后，以一个三维框架结构作为案例进行分析。分析表明，结构承载能力和失效模式取决于梁柱连接以及柱底的转动约束程度。梁柱之间的中间约束程度可获得最大的耐火性，而更高的约束会导致不利的侧移失效模式。该案例研究展示了新进展所引入的功能，并表明连接对整体响应的影响是复杂的，这证明了在火灾中结构设计和参数分析需要实用的数值方法。