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

3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS
Similar results are obtained for the TM-2 and JB1-3 specimens. In order to verify
the quality of these analyses, the values of J-integral for different paths 1, 5, 10
and 15 are plotted in Figure 3.41 as a function of the applied displacement with
reference to the specimens ITS2. More specifically, 1 represents the J-integral
computation from the first ring of elements abutting the crack tip whilst 15
corresponds to the path surrounding all the elements of the “spider web” mesh
illustrated in Figure 3.29b. The values of J1, J5, J10, and J15 agree with each
other entailing path independence at the given applied displacement. It is
worthwhile to recall that the estimate provided through the first ring of elements
surrounding the crack tip does not provide high accurate results (Bursi et al, 2002).
Residual stress effects
Rapid uneven heat removal in welded connections entails large welding-induced
residual stresses that can influence the joint behaviour in several ways. A detailed
investigation of these effects for welded beam-to-column moment connections can
be found in (Zhang et Dong, 2000). For the ITS connections of 12 mm thickness,
an idealised residual stress pattern like the one highlighted in Figure 3.28 has been
used, assuming a crack length equal to 1.30 mm and considering an overmatching
weld. Relevant results are reported in Figure 3.42a and Figure 3.42b: results show
clearly that the presence of residual stresses increases the toughness demand.
REACTION FORCE (kN)
90
350
300
250
200
150
100
50
0
W/o residual stresses
With residual stresses
0 1 2 3 4 5
DISPLACEMENT (mm)
CTOD (mm)
1
0.8
0.6
0.4
0.2
0
CTOD c
W/o residual stresses
With residual stresses
0 1 2 3 4 5
DISPLACEMENT (mm)
(a) (b)
Figure 3.42. (a) Predicted force vs. displacement and (b) CTOD vs. displacement of TM-2
specimens with and without residual stresses
The same idealised residual stress pattern has been used also for the ITS
connections with 18 mm thickness with a crack length equal to 2.34 mm and for the