Analysis and modelling of the seismic behaviour of high ... - Ingegneria
Analysis and modelling of the seismic behaviour of high ... - Ingegneria
Analysis and modelling of the seismic behaviour of high ... - Ingegneria
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6. SUMMARY, CONCLUSIONS AND FUTURE PERSPECTIVES<br />
web panel yielding, <strong>the</strong>y can exhibit favourable ductility <strong>and</strong> energy dissipation<br />
properties.<br />
As far as <strong>the</strong> underst<strong>and</strong>ing <strong>of</strong> <strong>the</strong> low-cycle fracture <strong>behaviour</strong> <strong>of</strong> ITS, CTS, <strong>and</strong><br />
CJ connections is concerned, experiments <strong>and</strong> numerical analyses under<br />
monotonic <strong>and</strong> cyclic loading have provided insights in order to develop rules able<br />
to reduce fracture in <strong>the</strong> aforementioned connection components. The main<br />
conclusions <strong>of</strong> this study follow.<br />
246<br />
vi. When proper consideration is given to material selection <strong>and</strong> detailing,<br />
extended end plates show a cyclic performance adequate for <strong>seismic</strong><br />
design. The considered joints exhibit a plastic rotation greater than 35<br />
mrad; <strong>the</strong>refore, <strong>the</strong>y can be classified as ductile in accordance to<br />
Eurocode 8 (2002). In detail, test results on isolated bolted Tee stubs as<br />
well complete extended end plate bolted joints have shown that <strong>the</strong> overall<br />
<strong>behaviour</strong> <strong>of</strong> <strong>the</strong> specimens under investigation is governed by <strong>the</strong> material<br />
endowed with <strong>the</strong> lowest strength, viz. <strong>the</strong> base metal, in which yielding<br />
occurs, effectively. In fact, <strong>the</strong> weld metal persists in <strong>the</strong> elastic regime<br />
while <strong>the</strong> contiguous zones are weakened owing to <strong>the</strong> sharp <strong>the</strong>rmal<br />
treatments <strong>and</strong> to structural as well as shape discontinuities.<br />
vii. Component cyclic tests enable identification <strong>of</strong> <strong>the</strong> failure mode. Moreover,<br />
<strong>the</strong>y allow <strong>the</strong> Code requirements on <strong>the</strong> rotational capacity <strong>of</strong> <strong>the</strong> joint to<br />
be checked. Moreover, <strong>the</strong> mechanical models provided by <strong>the</strong> Eurocodes<br />
to determine <strong>the</strong> stiffness <strong>and</strong> strength characteristics <strong>of</strong> <strong>the</strong> individual<br />
components showed little agreement with <strong>the</strong> experimental data.<br />
viii. A component model, which approximates <strong>the</strong> cyclic response <strong>of</strong> <strong>the</strong> joints<br />
on <strong>the</strong> basis <strong>of</strong> <strong>the</strong> responses <strong>of</strong> <strong>the</strong> elemental components, does not<br />
seem to possess sufficient accuracy. Conversely, <strong>the</strong> use <strong>of</strong> macro-<br />
components, incorporating some <strong>of</strong> <strong>the</strong> interaction effects among<br />
elemental components, appears to be more adequate.<br />
ix. The simulations relevant to isolated Tee stub <strong>and</strong> Complete Joint<br />
connections indicate that <strong>the</strong> numerical model with isotropic hardening rule<br />
is able to capture both <strong>the</strong> monotonic <strong>and</strong> <strong>the</strong> cyclic responses but is not<br />
able to reproduce properly stiffness <strong>and</strong> strength degradation.<br />
x. A number <strong>of</strong> parametric analyses have been performed by considering<br />
fractures initiating from weld-root defects by means <strong>of</strong> <strong>the</strong> onset cracking<br />
method. Conclusions drawn from <strong>the</strong> models indicate that:<br />
a. fracture driving force dem<strong>and</strong>s are reduced by using fillet welds<br />
matching <strong>the</strong> end plate material;<br />
b. welding-induced residual stresses increase <strong>the</strong> fracture dem<strong>and</strong>;