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

3. SEISMIC BEHAVIOUR OF BOLTED END PLATE BEAM-TO-COLUMN STEEL JOINTS
+ +
define the coordinates (ey , Fy ), of concern for the serviceability limit state.
Imposing the condition F + + + +
= Fy = Fu the ultimate displacement capacity eu can be
+ +
evaluated. Being Fu < Fmax , this definition implies a certain level of strength
degradation. Such procedure can also be applied to the non-linear force-
displacement envelope of the cyclic response of a specimen and therefore, the
+ +
ultimate displacement ductility factor eu /ey can be evaluated also in a cyclic
regime.
F
(F y + ,ey + ) (F p + ,ep + )
(F e + ,ee + )
K e +
K e,r +
K h +
(F max + ,emax + )
+ + (Fu ,eu )
Envelope
Trilinear approx.
Bilinear approx.
Figure 3.9. Bi- and tri-linear fits of a force-displacement envelope
To acquire comprehensive sets of information from the specimens, the so-called
Complete Testing Procedure proposed by the European Convention for
Constructional Steelwork (ECCS Procedure, 1986) was used. This sequential
displacement test protocol SDTP-1, which is illustrated in Figure 3.4a, is adopted to
acquire data on the specimen capacity such as the maximum strength, ultimate
+ +
displacement ductility eu /ey , maximum absorbed energy, etc. A variant of this
procedure, labelled SDTP-2, and suitable to ITS and CTS is depicted in Figure
3.4b. The procedure SDTP-3 illustrated in Figure 3.4c, is characterized by a set of
equi-amplitude constant displacements at 6e +
y, in agreement with the Cumulative
Damage Testing Program (1992). This procedure provides the basis for developing
fatigue-life relationships. Moreover, additional test protocols were conceived to
investigate the displacement sequence effects on cumulative damage. In
particular, the SDTP-4-SDTP-6 test protocols illustrated in Figure 3.4d-f, are
characterized with large displacement reversals reproducing seismic pulses
superimposed upon constant amplitude displacement fluctuations. Finally, the
SDTP-7 test protocol is plotted in Figure 3.4g and was derived from simulations on
steel frames exposed to an artificial accelerogram matching the Type 1 elastic
response spectrum suggested in Eurocode 8 (2002) for subsoil class A. This type
of displacement sequence provides a convenient benchmark for compare random
e
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