Keywords: partially restrained connection, high strength steel, frame model, spring stiffness, strain softening, non-linear, finite element.

The paper discusses the frame analysis using three-dimensional finite element models to investigate the influence of partially restrained (PR) connections with high strength steel on steel building structure frameworks. Rigorous application of the finite element computing package ANSYS 10.0 has been used to analyze the structural behaviour of the frames. The main focus of this paper is the development of finite element modelling procedures for the computational frame analysis of PR connections with strain softening effects. The softening effects were investigated due to the response from the connection stiffness and the bending of the beam, which has been the main driving force behind the development of new nonlinear structural design and analysis methods. Since the softening effects were neglected by many researchers due to the lack of convergence to a physically meaningful solution, this paper presents three dimensional finite element modelling to numerically model irreversible deformations, accompanied by the intense localisation of deformation and softening up to complete failure. Computational analysis of semi-continuous composite steel frame connections has been well predicted in terms of strength and deformation capacities [1,2].

As it is well known, the bound theorems underpinning the collapse load estimation of ductile structures requires an assumption of perfect plasticity. They are invalid for the class of structures, such as those being considered here, that exhibit local softening. A method has been proposed, based on the same conditions governing the path-independent state problem, for capturing the maximum load multiplier characterizing the one parameter proportionally applied loading regime.

When a PR connection is applied to the portal frame, there is a significant influence of the stiffness rigidity of the beam-column and column base connection with different responses under strain softening effects. The higher stiffness of the connection gives better resistance in the vertical deflection of the main beams for the non-sway frame. The presence of the high strength angles and endplates will reduce the connection weight yet with the higher capacity with a reduction in strain softening effect. It has been demonstrated that simplified portal frame analysis with non linear spring elements gives a significant role to predict the behaviour of PR connections due to strain softening effect up to complete failure. From these models it will be possible to establish new design methods for frame design utilising the strength and stiffness of PR connections with high strength steel utilising beam strain softening.

1

S. Taufik, R.Y. Xiao, "Numerical Modelling of Semi-continuous Composite Connections with High Strength Steel", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 153, 2007. doi:10.4203/ccp.86.153

2

R.Y. Xiao, C.D. Fisher, "Site monitoring and computational analysis of semi-continuous composite steel frame structure", International Conference of Connections in Steel Structures: Steel Connections in the New Millennium, Roanoke, Virginia, USA, October 2000.

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