Keywords: beam-column, shell element, contact element, three-dimensional, non-linear, finite element, stress-strain, moment-rotation.

This paper shows how simplified finite element modelling of beam-column bolted connections with shell elements may predict structural performance with more efficient analysis. The result presented in the paper is based on the moment-rotation relationships, the connection behaviour and employs shell and contact elements. Numerical modelling by three dimensional finite element analysis of beam-column connections has been done by many researchers. The three dimensional analysis of bolted connections using shell elements has been well verified [1] and [2]. Since the bolt pretension and slip are a more important parameter, therefore the bolt model and contact element require the modelling to be as accurate as possible [3]. The behaviour of angle bolted connections applying high strength steel shell elements has been done as described in reference [4]. Nevertheless, the modelling approach still requires simplifications in order to reduce the computational effort.

The double web angle (DWA), top and seat angle (TSA) connections are investigated in this study. The finite element of these connections is then presented and the results are compared with the previous test data, and finally the behaviour of the connection with mild carbon steel and high strength steel is predicted. The configurations of angle bolted connections in the finite element modelling are modified by placing the angles either to beam web and column flange or to beam flange and column flange. The influence of angle thickness and strength to the connection behaviour is determined. The contact between angle and either the column or the beam is considered to capture the true behaviour of the connection through the finite element modelling.

ANSYS version 8.1 which is a general purpose finite element package is selected to carry out the numerical modelling and analysis. Non-linear angle bolted connection models are symmetric about the centre of the beam web and no lateral displacement is assumed, so only one side of the plane of symmetry is modelled. The beam, column and angle are simplified by using SHELL143 elements. The bolt head and nut are modelled as hexagon solid elements. The bolt shank is modelled using a spar element connecting the farthest corner nodes of the head and nut to each other. The effective area of the bolt is split one twelfth equally among the spar elements. The bolt holes are modelled as circular. Bolt pretension caused by bolt tightening is simulated by applying equivalent initial strains to bolt shank elements. The model of interface element is designated as an initial gap line of 3D point to point contact elements. The normal stiffness value and sticking stiffness value are based upon the maximum expected force divided by the maximum allowable surface displacement. A high contact stiffness was specified to prevent excessive penetration of the contact nodes. Trilinear and multilinear elastic-plastic approaches are used to determine the material properties of mild carbon steel and high strength steel for the FE model.

The initial stiffness of FE model is well predicted by verification with previous experimental testing. The effect of angle thickness gives slightly change of the initial stiffness, whilst the thicker one will be more pronounced on the slippage of the angle bolted connections. The plastic strain and stress patterns of high strength angles are very similar, in general. The model presented gives excellent results for increasing the moment and the rotational capacity significantly. The connection capacity of high strength thicker angles of TSA is slightly more than that of DWA connections except for the connection with higher beam depth and very high strength angles. The high strength angles give a significant proportion of maximum stress distribution, whereas the beam and column are kept with mild carbon steel. Solid elements are suitable for simple connection problems, but shell elements are best suited for more complicated structures such as beam to column connections. The additional flexibility allows the plate bending to be modelled accurately. Thick endplate connections provide additional rotational stiffness and moment capacity but the rotation capacity may be compromised through bolt failure. Thin endplates provide enough deformation capacity to allow semi rigid-connection design but yielding of the angle plate may produce excessive deflection. Also the thin endplate increases the prying forces with an associated increase in bolt loads

1

Bahaari M.R. and Sherbourne A.N., "3D simulation of bolted connections to unstiffened columns-II. extended endplate connections", J Constr Steel Res 40:3, 189-223, 1996. doi:10.1016/S0143-974X(96)00049-1

2

Sherbourne A.N. and Bahaari M.R., "3D simulation of bolted connections to unstiffened columns-I. T-stub connections", J Constr Steel Res 40:3, 169-187, 1996. doi:10.1016/S0143-974X(96)00048-X

3

Citipitouglu A.M., Haj-Ali R.M. and White D.W., "Refined 3D finite element modeling of partially restrained connections including slip", J Constr Steel Res 58:5-8, 995-1013, 2002. doi:10.1016/S0143-974X(01)00087-6

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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