Principles of a component-based connection element for the analysis of steel frames in fire

► An approach is developed to model connections between steel members in fire. ► Connections experience large variations of normal forces and moments in fire. ► Behaviour cannot be represented by moment and rotation, as at ambient temperature. ► A component-based approach is the only feasible method in fire. ► The creation of connection elements from assemblies of components is described. In this paper an approach is developed for practical modelling of the in-plane behaviour of connections between steel structural elements in global 3-dimensional frame analysis when structures are subject to heating by accidental fires. Because of the interactions between high deflections, thermal expansion and material weakening at high temperatures, connections are subject to considerable variation of both normal forces and moments in fire, so that it is insufficient to represent their behaviour simply in the moment–rotation terms which are usually adequate at ambient temperature. In order to analyse this behaviour reliably, use of the component-based approach is the only feasible method (short of creating highly complex finite element models) which can be included in non-linear, full-frame or subframe, numerical modelling. In previous work non-linear “spring” formulations have been developed and validated for the principal components which occur in the most commonly used steel-to-steel joint details, particularly for endplate connections, taking into account the local geometry, temperature and loading history. The principles governing the creation of connection elements, presenting just two nodes to the connected structural members, from assemblies of such components, are described for connections subject predominantly to two-dimensional structural actions.