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

5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES
In composite connections, the concrete compression strut may be mobilised in
resisting the shear either due to the presence of the horizontal plates welded to the
column or simply due to friction and flexural forces acting in the steel column
flanges. By means of a set of elements extracted in the concrete between the
stiffeners and the web panel of the steel profile, it was possible to monitor the
evolution of the principal stresses of compression for different imposed top
displacement.
As evidenced in Table 5.17, with the increasing of the displacement imposed at the
top of the column, high stresses of compression are mobilized in the concrete strut.
For a displacement equal to 6ey all the concrete in the zone reached the value of
40 MPa that represent the maximum allowed compression strength. Nevertheless,
the effect of the confinement due to the presence of the steel profile and the
stiffeners permits to reach greater value for an amplification of the top
displacement. Finally, at an imposed displacement equal to 10ey the concrete in
the interior zone and around the joint is crushed. The numerical results are in a
good agreement with the experimental test, as evidenced in Figure 5.43.
Figure 5.43. Failure of the joint during the experimental tests
The shear resistance given by the concrete horizontally compressed by the
elements inside the column Vj,hbf, is determined through a standard Stress Block
Model. For a good development of the Horizontal Bearing Mechanism it is
important to provide a sufficient concrete confinement. The provided amount of
stirrups in the tested specimens seems to be adequate to this aim.
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