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

3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS
i. When proper consideration is given to material selection and detailing,
extended end plates show a cyclic performance adequate for seismic
design. The considered joints exhibit a plastic rotation greater than 35
mrad; therefore, they can be classified as ductile in accordance to
Eurocode 8 (2002). In detail, test results on isolated bolted Tee stubs as
well complete extended end plate bolted joints have shown that the overall
behaviour of the specimens under investigation is governed by the material
endowed with the lowest strength, viz. the base metal, in which yielding
occurs, effectively. In fact, the weld metal persists in the elastic regime
while the contiguous zones are weakened owing to the sharp thermal
treatments and to structural as well as shape discontinuities.
ii. Component cyclic tests enable identification of the failure mode. Moreover,
they allow the Code requirements on the rotational capacity of the joint to
be checked. Moreover, the mechanical models provided by the Eurocodes
to determine the stiffness and strength characteristics of the individual
components showed little agreement with the experimental data.
iii. A component model, which approximates the cyclic response of the joints
on the basis of the responses of the elemental components, does not
seem to possess sufficient accuracy. Conversely, the use of macro-
components, incorporating some of the interaction effects among
elemental components, appears to be more adequate.
iv. The simulations relevant to isolated Tee stub and Complete Joint
connections indicate that the numerical model with isotropic hardening rule
is able to capture both the monotonic and the cyclic responses but is not
able to reproduce properly stiffness and strength degradation.
v. A number of parametric analyses have been performed by considering
fractures initiating from weld-root defects by means of the onset cracking
method. Conclusions drawn from the models indicate that:
a. fracture driving force demands are reduced by using fillet welds
matching the end plate material;
b. welding-induced residual stresses increase the fracture demand;
c. connections with σy/σu = 0.9 exhibit reduced fracture driving force
demands but also limited plastic regions. The yield-to-ultimate strength
reduction must comply with the requirements of plastic analysis.
Besides, the study is currently concentrating on the damage evolution aspect both
for the components and the joint. The availability of adequate damage assessment
methods is a pre-requisite to the development of reliable hysteretic models for
research as well for design purposes.
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