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

3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS
CJ connection with 18 mm thickness with the same crack length. The results are
then compared. The maximum CTOD required along the end plate width close to
the weld toe predicted both by 2D and 3D analyses is depicted in Figure 3.43. The
3D analysis reveals a significant gradient across the width of the flange with a peak
value in correspondence with the web. The CTOD ratio between 3D and 2D FE
models is around 16 per cent.
CTOD (mm)
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
2D Simulation
3D Simulation
0 20 40 60 80 100 120 140 160 180
FLANGE WIDTH (mm)
Figure 3.43. 2D versus 3D CTOD distribution at the weld toe for a crack
depth of 2.34 mm
Yield-to-ultimate stress ratio effects
The plastic hinge region in a steel structure decreases as the yield-to-ultimate
strength ratio σy/σu increases. In fact, a smaller yielded region imposes greater
inelastic strain demands to achieve a specified plastic deformation. Since the
production of American structural steel has resulted in steel with much higher ratios
(Frank, 1997), recently published specifications from AISC (1997) recognized this
effect and limited the yield-to-ultimate strength ratio to 0.85. A similar limitation is
required by Eurocode 3 (2001), when plastic analysis has to be performed.
In order to study the yield-to-ultimate strength ratio effect on the joint configuration
with 12 mm and 18 mm thickness, two strength ratios for the end plate material
have been considered. More specifically, for the TM-2 specimen, σy/σu has been
chosen to be 0.45 and 0.90 whilst the corresponding specimens are designated
ITS2-45 and ITS2-90, respectively. However, two crack lengths equal to 1.30 mm
and 2.86 mm have been considered for the specimen ITS2-45 and ITS2-90,
respectively, to take account of the increase of crack-initiation threshold with the
reduction of a strain hardening amount (Barsom and Rolfe, 1987). The reaction
force vs. the controlled displacement of the TM-2 model is shown in Figure 3.44a,
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