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

3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS
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M col,t
Vcol,t
f
f
c
N
N
col,b
V
col,t
col,b
M col,b
b
V beam
M beam
N beam
Figure 3.8. Definition of rotations for a Complete
Joint
3.4.4 Testing procedure
Predefined representative displacement histories are usually applied in order to
characterize the behaviour of specimens under hysteretic loading. The problem of
the displacement pattern arises especially under seismic loading, as unique fatigue
relationships are strictly valid only for constant-amplitude displacement reversals.
Real structures, however, seldom conform to this ideal as they can be subjected to
multitude of displacement patterns of varying degrees of complexity. In these
instances, probability-density curves able to characterize random-amplitude
displacements should be employed. In order to reduce the problem complexity, a
heuristic approach is adopted in this study, applying to the specimens several
displacement histories lying between the extremes of constant-amplitude and
random-amplitude displacement reversals.
In order to define conveniently displacement patterns, a conventional elastic limit
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state characterized by the displacement ey and the corresponding force Fy can be
defined on the first part of each non-linear response envelope obtained from
monotonic tests as depicted in Figure 3.9, schematically. The tri-linear
approximation of each curve, is determined on the basis of best-fitting and of the
equivalence of the dissipated energy between the actual non-linear response and
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the idealized tri-linear approximation up to (emax , Fmax ). Then, the linear elastic
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response with slope Ke and the linear strain-hardening response with slope Kh