This paper presents a simplified robust 2-noded connection element for modelling the behaviour of partial end-plate connections under fire conditions. In this new model the partial end-plate connection is modelled as a 2-noded nonlinear spring element. The characteristics of the springsuch as stiffness, tension, compression, shear strengths and bending moment resistance -are determined based on each component of the connection. It is well known that the rotational response of a partial end-plate connection comprises of two stages, due to the shift of the compression centre of the connection from the end of the endplate to the centre of the beam bottom flange at large rotation. This two stage behaviour is considered in the model proposed. Compared to normal component-based models the most significant of the current model is that this simplified model has very good numerical stability under static solver condition. The model also retains the advantages of both the simple and component-based models. Fourteen tests of partial end-plate connection previously conducted by other researchers were used to validate the proposed model. It is evident that the model is capable to predict the behaviour of flexible end-plate connections under fire conditions. In order to investigate the influences of the connections on the behaviour of steel structures, a series of numerical studies has been conducted on a 2D steel frame, subjected to ISO834 Fire and Natural Fire. It is clear that the model can be used to represent the partial end-plate connections in performance-based fire resistance design of steel-framed composite buildings.

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According to full-scale fire tests, it is noticed that tensile membrane action within the concrete floor slabs plays an important role in affecting the fire resistance of composite buildings. It is well known that the development of tensile membrane actions relies on the vertical support along the edges of the slab panel. However, there is at present a lack of research into the influence of vertical supports on the tensile membrane actions of the floor slabs. In this paper, the performances of a generic three dimensional 45m x 45m composite floor subjected to ISO834 Fire and Natural Fire are investigated. Different vertical support conditions and three steel meshes are applied in order to assess the impact of vertical supports on tensile membrane action of floor slabs. Unlike other existing large scale modelling which assumes the connections behave as pinned or rigid for simplicity, two robust 2-node connection element models developed by the authors are used to model the behaviour of endplate and partial end-plate connections of composite structures under fire conditions. The impact of connections on the 3D behaviour of composite floor is taken into consideration.The load-transfer mechanisms of composite floor when connections fail due to axial tension, vertical shear and bending are investigated. Based on the results obtained, some design recommendations are proposed to enhance the fire resistance of composite buildings.

The calculation of large bending deflections of thin plates by available techniques are either too difficult to use or are limited to deflections which are below 20 percent of the plate’s length and/or width. The present method predicts, and is substantiated by experiment, the maximum deflections of such thin plates within a few percent wherein the deflections are larger than half the length and/or width of the thin plate.

In this paper, the performances of a generic three dimensional 45m x 45m composite floor subjected to ISO834 Fire and Natural Fire are investigated. The influences of reinforcing steel mesh and vertical support conditions on the tensile membrane action of floor slabs are investigated in details. Two robust 2-node connection element models developed by the authors are used to model the behaviour of end-plate and partial end-plate connections of composite structures under fire conditions. The impact of connections on the 3D behaviour of composite floor is considered. Based on the results obtained, some design recommendations are proposed to enhance the fire safety design of composite buildings.