Keywords: local buckling, square steel tube member, truss element, elastoplastic buckling, thermodynamics, plastic dissipation, softening.

It is important to analyze the collapse behavior of designed structures. For the strength degradation behavior of the structures composed of square steel tube members, it is necessary to evaluate local buckling. In order to evaluate the influence of local buckling, we generally use the finite element method with a discrete model. But it is very costly to evaluate the local buckling using a discrete model because the model requre many elements to acheve accurate results.

So far, to analyze a large structural model economically, a special simplified method such as the simple plastic hinge model or the multi spring model were proposed, and the strength degradation by the local buckling was taken into account in the elements. When we analyze truss members, we generally use a multi-spring model, and the influence of local and overall buckling is reflected in load-displacement relationship. But the process to decide its restoring force characteristic is not systematic because the theoretical background and validity of the mechanics in its treatment are not clear.

In previous papers [1], we proposed a consistent and convenient analytical method to evaluate the local buckling and overall buckling behavior of H-section steel truss members. In this method, its formulation is based on thermodynamics and we regard the effect of the local buckling as the softening, that is, multi yield surfaces in the space of stress resultant that move according to the degree of local buckling. And this softening property is derived from the buckling property of the plate, corresponding to plastic dissipation. Furthermore, in a previous paper [2], we extended this local buckling evaluation method to a square steel tube member, and proposed a beam element considering local buckling behaviour.

Then in this paper, we will propose a consistent and convenient truss element which is able to evaluate local and overall buckling behavior of square steel tube members. We describe the plastic buckling for a member of usual slenderness ratio and width-thickness ratio. Then we consider plastic and local buckling free energy component and by using the Clausius-Duhem inequality and the principle of maximum plastic dissipation, we obtain the basic equations of elastoplastic buckling. Furthermore, we approximately apply the hypothesis of stress block to the local buckling stress distribution, and obtain the yield function with local buckling. Finally we will examine the validity of the present element through some numerical examples.

1

T. Ohtsuka, S. Motoyui, "Analytical Evaluation for Local and Overall Buckling Behaviour of H-Section Truss Members", in B.H.V. Topping, G. Montero, R. Montenegro, (Editors), "Proceedings of the Eighth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 189, 2006. doi:10.4203/ccp.83.189

2

T. Ohtsuka, S. Motoyui, "Analytical Evaluation of Local Buckling Behaviour in Square Steel Tube Members", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 220, 2008. doi:10.4203/ccp.88.220

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £145 +P&P)