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

4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS
The strut and tie mechanisms to be activated in the slab depend on the joint
flexibility. The numerical analyses carried out under sagging bending moment have
evidenced the presence of high gradients of compression stresses in front of the
column flanges. It is impossible to appreciate the formation of the idealized
Mechanism 2, proposed in Section 4.5.1. In fact, in the portion of the concrete slab
around the column, the numerical model evidences tensile stresses that do not
permit the presence of an idealized concrete strut. This means that, under sagging
bending moment, the resistance of the composite connection depends only on the
resistance of the proposed Mechanism 1. The experimental loss of resistance of
the joint is due to the high level of stresses that the concrete slab should transmit
from the composite section of the beam to the column.
(a)
(b)
Figure 4.43. Evolution of the compression stress distribution in the concrete slab due to: (a)
activation only of Mechanism 1; (b) Activation of Mechanisms 1 and 2
On the basis of the observations that have been brought to light, it is possible to
design some constructional details that permit the formation of the Mechanism 2 in
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