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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3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS<br />
On <strong>the</strong> o<strong>the</strong>r h<strong>and</strong>, <strong>the</strong> corresponding strain distributions <strong>high</strong>lighted in Figure 3.45<br />
indicate that <strong>the</strong> end plate yield zone is smaller for <strong>the</strong> specimen labelled ITS2-90.<br />
Therefore, a balance between <strong>the</strong> two opposite requirements has to be found.<br />
(L1)<br />
(L2)<br />
Figure 3.45. Equivalent plastic strain (PEEQ) distributions <strong>of</strong> TM-2 specimens at two levels<br />
<strong>of</strong> applied displacements: (a) σy/σu=0.45 (ITS2-45); (b) σy/σu=0.90 (ITS2-90)<br />
As far as <strong>the</strong> ITS connections with 18 mm thickness is concerned, two strength<br />
ratios σy/σu for <strong>the</strong> end plate material equal to 0.60 <strong>and</strong> 0.90 have been considered<br />
<strong>and</strong> <strong>the</strong> corresponding specimens are called ITS3-60 <strong>and</strong> ITS3-90, respectively.<br />
Again, to take into account that <strong>the</strong> crack-initiation threshold increases with a<br />
strain-hardening reduction, two crack lengths equal to 2.34 mm <strong>and</strong> 4.95 mm have<br />
been chosen for <strong>the</strong> specimen ITS3-60 <strong>and</strong> ITS3-90, respectively. Similar results<br />
are obtained, as shown in Figure 3.46.<br />
So far we have estimated critical states both in 2D <strong>and</strong> 3D models through <strong>the</strong> use<br />
<strong>of</strong> a critical value <strong>of</strong> <strong>the</strong> CTOD, which amounts to 0.31 mm for <strong>the</strong> joints under<br />
examination. It is possible to define critical stress states through <strong>the</strong> use <strong>of</strong><br />
response indices, which do not require a crack <strong>modelling</strong>. One <strong>of</strong> <strong>the</strong>se indices is<br />
<strong>the</strong> Rupture Index related to <strong>the</strong> stress triaxiality ratio σm/σeff, where σm defines <strong>the</strong><br />
hydrostatic stress <strong>and</strong> σeff is <strong>the</strong> von Mises stress. Several FE analyses were<br />
conducted to estimate this index at <strong>the</strong> weld toe. 2D simulations confirm that end<br />
plates with σy/σu = 0.6 exhibit a favourable value <strong>of</strong> <strong>the</strong> triaxiality ratio <strong>of</strong> about<br />
0.49, implying a ductile <strong>behaviour</strong>. The corresponding 3D analyses yield a<br />
maximum triaxiality ratio sampled at <strong>the</strong> weld toe in <strong>the</strong> middle <strong>of</strong> <strong>the</strong> end plate <strong>of</strong><br />
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