The behaviour of steel fin plate connections in fire

Steel joints have always been considered as important parts of any structural steel building because they provide the strong links between the principal structural members. The properties and behaviour of joints in both steel and composite structures have been widely studied for some time. The focus has recently been on improving the design of structural frames by taking advantage of realistic connection moment-rotation response. This has necessitated the development of an effective and practicable methodology to describe steel connection behaviour, despite its inherent complexity. Although, the evaluation of steel connections' performance at ambient temperature has been a continuous research topic, the investigation of steel connections at elevated temperatures has only recently been tackled by researchers. However, the determination of the behaviour, available strength and stiffness of moment connections in fire conditions has been a dominant theme in these research works. Moreover, over a number of years the Component Method has been developed to describe the moment-rotation characteristics of end-plate connections, and the method is now included in Eurocode 3. To date, most of the research conducted on steel connections using the component method has focused on relatively stiff and strong connections - flush end-plates and extended end-plates. The modelling of more flexible ("pinned") connections using the Component Method has not received much attention, since the benefits arising from consideration of their behaviour in overall frame response are usually modest. However, in fire conditions connections are subject to complex force combinations of moment and tying forces, as well as vertical shear forces, and the real behaviour, even of nominally pinned connections, can have a significant effect on the overall response of the frame. To date very little information on the behaviour and the resistance of simple shear connections in fire conditions has been generated. Fin plate shear connections, which are economic to fabricate and easy to use in erection, are among these shear connections which are assumed to act as pins in normal service conditions In this research, the behaviour and robustness of simple fin plate beam-to-column connections has been investigated, under the conditions of catenary tension from highly deflected beams which occurs in fire. In addition, detailed investigations have been made on applying the component method approach to this connection at both ambient and elevated temperatures. ABAQUS software has been selected to create a very detailed 3D finite element model. This is a complex model accounting for material nonlinearity, large deformation and contact behaviour. The connection model has been analysed through the elastic and plastic ranges up to failure. Bolt shear and bending, plate and web bearing have been observed as failure modes. A comparison between available experimental data at ambient and elevated temperatures and FEA results shows that the model has a high level of accuracy. However, by implementing the FE model the opportunity was then available to explore the connection tying resistance and the application of the Component Method to the fin plate connection. An intensive investigation has been conducted to develop a representation of this connection type via a simplified component model, enabling prediction of the connection response at both ambient and elevated temperatures. The three main components of a fin-plate connection have been identified as plate bearing, bolt shearing and web-to-plate friction. These components have been described in detail at ambient and elevated temperatures via intensive parametric FE analyses, leading to a simplified component model of a fin plate connection. This model has been evaluated against FE models of complete fin plate joints. Eventually, a fin plate connection spring model is proposed and successfully evaluated for tying, rotation, and shear actions. The Component Model presented in this research offers an opportunity to explore complicated behaviour of fin plate shear joints, and can be incorporated into frame analysis in fire conditions.