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

5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES
and shear resistance of the steel sections reduces of a half factor, while the
second one guarantees the resistance in bending to be half of that belonging to the
original section. Nevertheless, by diminishing the geometrical properties of the
concrete sections we obtained a reduction of the bending resistance equal to one
fourth of the original section. Hence, the assumptions made for the reduction of the
steel profile properties were not adoptable. Indeed, it was necessary to calculate
the reduced steel sections following the design criteria already presented in a
previous paragraph for the full-scale steel-concrete composite columns, and briefly
summarised below:
a. the steel section should at least be able to take alone the design axial force of
the seismic loading case;
b. the steel section alone (not acting composedly) should be able to substitute the
deficient concrete section;
c. the sections have been chosen in order to not modify the local stiffness EI of
the columns and the total stiffness of the original concrete structure (maximum
level of modification of the order of 10%);
d. the sections have been chosen in order to achieve a favourable performance
both along their major axis bending and along their minor axis bending.
In the following Figure 5.19 the reduced composite column cross sections adopted
in the experiments at the University of Trento are shown.
Figure 5.19. Reduced sections for the composite columns to be tested
From these sections, corresponding to the respective load cases under study, we
extrapolated the scaled 3D composite columns to be analysed. Each cross
composite section generated four scaled samples, two with long steel profile (with
or without steel plates in the joint), and two with short steel profile in the critical
length (with or without horizontal steel plates) as illustrated in Figure 5.20.
Therefore, to each design category (static and seismic) belong four composite
samples plus another scaled sample without the encased steel profile. The latter
operating as a comparison trial for the others. Also four tests along minor axis were
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