Keywords: steel joint, component method, seismic, hysteretic behaviour, cyclic, eurocodes.

The analysis of the behaviour of steel joints is very complex and requires the proper consideration of a multitude of phenomena, ranging from material non-linearity (plasticity, strain-hardening), non-linear contact and slip, geometrical non-linearity (local instability) to residual stress conditions and complicated geometrical configurations. The eurocode 3 design approach consists of the so-called component method that supplies procedures for the evaluation of the rotational behaviour of joints under monotonic static loading. It corresponds to a simplified mechanical model composed of extensional springs and rigid links, whereby the joint is simulated by an appropriate choice of rigid and flexible components.

Under cyclic loading, the behaviour of steel joints is further complicated by successive static loading and unloading. Usually, seismic events provoke relatively high amplitudes of rotation in the joint area, so that steel repeatedly reaches the plastic range and the joint fails after a relatively small number of cycles.

Unlike static monotonic situations, it is not yet possible to predict the moment-rotation response of steel joints under cyclic loading using the component method. It is the objective of this paper to present a component model for end-plate beam-to-column steel joints subjected to cyclic loading. In particular, the model is firstly applied to a series of experimental tests on steel joints carried out at the University of Coimbra. Subsequently, a parametric study is carried out for a range of geometries in order to provide design guidance for the use of partial strength dissipative joints in seismic regions.

Given the number of components that are active in a beam-to-column joint and the complexity of the problem, the following assumptions were adopted in the development of a cyclic component model:

(i)

Hysteretic behaviour is only modelled for a small number of dissipative components, denoted as critical components;

(ii)

The remaining components are modelled as linear elastic with a failure deformation corresponding to the failure load of the component for brittle components and the plastic load for ductile components;

(iii)

The critical components are defined on the basis of the evaluation of the rotational behaviour both for hogging and sagging bending moments under static monotonic loading.

The cyclic model is developed for end-plate beam-to-column steel joints with transverse stiffeners. In this case the critical components are the column web panel in shear and the end-plate in bending.

In order to explore the versatility of the proposed cyclic joint model, a parametric study is presented that tries to assess the influence of the relative behaviour of the two controlling components on the global hysteretic response.

A few issues still remain open before the widespread application of this model is possible: (i) extensive validation with experimental results; and (ii) specification of a simple hysteretic model for the pinching and degradation parameters of the end-plate in bending.

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