Keywords: flush end plate connection, beam-column, high strength steel, semi-rigid, three-dimensional, non-linear, finite element, stress-strain, moment-rotation.

This paper presents a three dimensional (3D) finite element methodology to predict the behaviour of high strength bolted steel beam-column connections. Non-linear 3D continuum solid elements are used for all parts of the connection to investigate the structural performance of flush end plate connections between mild carbon steel and high strength steel. The analysis results of the moment-rotation relationship and behaviour characteristic of the connection with mild carbon steel and high strength steel are compared and discussed.

In references [1] and [2], the papers use the finite element method to analyze flush end-plate configurations. An ANSYS finite element model for flush end-plate joints with solid elements has been presented, where material non-linearities, contact surfaces and large deflection analysis were included in a non-linear solution [3]. Three dimensional finite element modelling of angle bolted connection with high strength steel has been well predicted [4].

The ANSYS finite element program was used to create a numerical model of a flush end plate connection. Simplified multi-linear stress-strain curves for the steel sections and bolt shanks were used. Failure of the model was described by the rate of convergence experienced for a sub-step of loading after yielding or through excessive deformation of components. In addition to material non-linearities, there are geometric non-linearities present due to the changing area of contact between the faces of the endplate. Three-dimensional eight node structural solid elements, SOLID45, are used to model beam, column and plate. Bolt head, shank and nut are idealized using eight-node isoparametric solid elements, i.e. SOLID185. The interactions between plate and column are simulated by 3D node-to-node contact element i.e. CONTACT178 elements. The PRETS179 pretension element is used for model preload in bolts. The material behaviour for all the elements was described by multi-linear stress-strain curves.

Flush endplate connections based on FE modelling with both unstiffened and stiffened column are also analysed with modern design codes. The observed failure moments from the finite element analysis, compared with the design predictions gives significance variation of value. Significant response from stiffener gives connection capacity increase significantly. The plots of Von Mises equivalent stress of the FEP connection with high strength end plate and mild carbon steel column are successful in predicting maximum stress of all connection members below their ultimate stress. The response from stiffener and high strength end plate gives moment connection capacity increase significantly.

The initial stiffness and moment capacity of FE model is well predicted by verification with previous experimental testing. The effect of plate thickness gives significance change of the initial stiffness, whilst the higher strength end plate will be more pronounced on the moment capacity of connection. Thick high strength endplate connections provide additional rotational stiffness and moment capacity but the rotation capacity may be compromised through bolt failure. Such a failure mode is not acceptable for semi-rigid frame design because a large rotation capacity is required to allow moment redistribution to occur effectively. Thin low strength endplates provide enough deformation capacity to allow semi rigid connection design but yielding of the endplate may produce excessive deflection. Also the thin endplate increases the prying forces with an associated increase in bolt loads. Higher strength end plates may delay the end plate yielding and excessive deflection. The moment capacity prediction of EC3 has been shown to be reasonable. The nature of the failure mode was predicted reliably for the simple connections studied. It is however clear that more complicated arrangements of stiffeners and bolts may prove inaccurate. Provided these inaccuracies do not lead to a brittle failure they are acceptable. The high strength end plate gives a significant proportion of maximum stress distribution, whereas the beam and column are kept with mild carbon steel. The moment rotation curve is very important parameter to predict the connection behaviour with high strength steel.

1

Shi, Y.J., Chan, S.L., and Wong, Y.L., "Modelling for Moment-Rotation Characteristics for End-Plate Connections", Journal of Structural Engineering, ASCE, 122, 1300-1306, 1996. doi:10.1061/(ASCE)0733-9445(1996)122:11(1300)

2

Bursi, O.S., and Jaspart, J.P., "Calibration of a Finite Element Model for Isolated Bolted End-Plate Steel Connections", Journal of Constructional Steel Research, 42, 225-262, 1997. doi:10.1016/S0143-974X(97)00056-4

3

Fanning P., Tucker M. and Broderick B., "Nonlinear Finite Element Analysis of Semi-Rigid Bolted End-Plate Connections", in Computational Techniques for Materials, Composites and Composite Structures, B.H.V. Topping (Editor), Civil-Comp Press, Edinburgh, 2000. doi:10.4203/ccp.67.9.3

4

Taufik S. and Xiao R.Y., "3D Finite element prediction of angle bolted connection with high strength steel", Proceedings of the fourth international conference on advance in steel structure, 13-15 June 2005, paper no. ISP-25, 2005. doi:10.1016/B978-008044637-0/50265-1

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