Analysis and modelling of the seismic behaviour of high ... - Ingegneria

3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS
response - influenced by the geometrical and mechanical parameters defining the
key structural components, i.e. the end plate, the bolts, the column flange and web,
the column panel zone - makes the experimental analysis vital research tool.
Numerous studies were also devoted to the simulation of joint behaviour through
numerical methods, in particular FE analysis with interesting results, which
complemented the test outcomes permitting their extension to a larger range of
cases of practical interest (Nethercot & Zandonini, 1988; Bose et al, 1996; Bursi
and Jaspart, 1997; Bursi and Jaspart, 1998; Bahaari and Sherbourne, 2000).
Despite important continuous advances in FE analysis, which enable more and
more refined approximations, the reliability of the results is still remarkably affected
by the importance of localised effects, e.g., the evolution of plate-contact area, bolt-
plate interaction, low ductility of the Heat Affected Zones (HAZ) near welds, etc.
Besides, the associated burden makes this approach unfeasible in design practice,
and its cost efficiency remains rather low even for research purposes. However,
the knowledge of the behaviour of end plate connections under static loading was
more than adequate to develop and validate design models, which meet the recent
demand of semi-continuous frame design.
An extended end plate connection consists of a plate with bolt holes drilled or
punched, and shop welded to a beam section. The connection is completed in the
field when the beam end is bolted to a column. The extended end plate connection
is termed “extended” because the plate extends above or below the flange that will
be in tension under monotonic loading. In the case of extended end plate devoted
to seismic design, the end plate is extended above and below beam flanges.
The behaviour of this type of connection under cyclic loading has been
investigated, though at a lower extent than for the static case, and the main
features clearly identified, including the stiffness and strength deterioration, the
dependence on the loading history, and the typical modes of failure (Ghobarah et
al, 1990; Ghobarah et al, 1992; Bernuzzi et al, 1996; Kukreti and Biswas, 1997;
Adey et al, 1998). On the one hand, the increasing degree of complexity of the
phenomena involved with respect to the monotonic case is apparent, like also the
higher difficulty in setting up a model capable of approximating the hysteretic
behaviour under any type of loading history, with the accuracy level required in
seismic design (Deng et al, 2000). On the other hand, recent studies pointed out
that moment resisting semi-continuous steel frames can possess a satisfactory
seismic performance at competitive cost (Nader & Astaneh, 1991), which
underlines once more the lack of simplified, yet reliable, design criteria and joint
models. Such a limited knowledge hampers the practical use of semi-rigid frames
in seismic areas, despite they are accepted by recent Codes (AISC, 1997 and
Eurocode 8, 2002).
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