Keywords: steel frame, end-plate joints, seismic behaviour, cyclic loading, finite element model.

Bolted end-plate joints are widely used in steel frames. They can be applied to connect either two steel members (e.g. beam-to-column or beam-to-beam connections) or a steel and a reinforced concrete member (e.g. column-base connection). Although this kind of joints have numerous practical advantages (fabrication, erection, etc.) their behaviour is usually rather complex, determined by the interaction of several phenomena. Consequently, a numerical model which is able to cover all the important components of the behaviour is necessarily complicated. The problem is even more complex if not only quasi-static loading is considered, but also seismic actions are taken into consideration. This is the reason why such models are not applied in the design practice and hardly can be found even for research purposes.

The presented research concentrates on steel-to-concrete bolted end-plate joints, which is the typical solution for the column-base connection of steel frames. Not only monotonic but also cyclic loading is applied, this latter being regarded as a simplified load model of seismic actions, which takes into consideration the alternate nature of earthquake loading but neglects the effect of loading velocity.

The development of the proposed numerical model is based on two principles. On the one hand the model should be able to follow all the phenomena which have crucial role in determining the joint's behaviour, while on the other hand it must provide results within a reasonable time by using the up-to-date hardware facilities. Since it is not realistic to entirely fulfil both these two opposing criteria it is necessary to have an appropriate compromise. For this reason it is assumed that this is the steel components which have primarily importance in the behaviour, while the concrete part has only secondary role. In other words it means that the steel components must be modelled more precisely than the concrete one.

The proposed model is based on finite element formulation, using layered shell finite elements for the steel plates (end-plate, column section). The bolts and the concrete part are taken into consideration approximately as a special foundation layer of the end-plate. Cyclic material models are used. For the steel plates a multi- surface (Mroz-type) model is applied, while for the concrete a one-dimensional cyclic model is used. The anchoring bolts are analysed separately by a special model to establish their force-displacement relationship, which then serves as the non- linear spring characteristics of the foundation layer. Contact-separation phenomena are also handled by the spring characteristics of the foundation layer of the end-plate finite elements.

All components of the model are systematically developed and tested. In every steps of the development the model results are compared to analytical, numerical or experimental results.

The paper gives a general view about modelling possibilities of end-plate joints under cyclic loading conditions, summarising all those requirements that seem to be fulfil to have an appropriate numerical model for the given problem. Based on [1] a set of examples of virtual tests is also presented, including material tests, virtual cyclic plate buckling tests, anchor bolt tests and T-stub tests. Finally, a demonstrative example is shown for the global analysis of an end-plate joint.

1

Ádány, S., "Numerical and experimental analysis of bolted end-plate joints under monotonic and cyclic loading", PhD Thesis, Supervisor: L. Dunai, Budapest University of Technology and Economics, 2000.

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