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

4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS
4.5 Seismic design of the composite joint
For moment resisting frame structures, the maximum structural ductility is attained
through the formation of global mechanisms (Gioncu et al., 2002). To this end, it is
necessary to foresee sufficient overstrength of the columns satisfying the relation:
where
110
M ≥ 1.3 ⋅ M
( 4.3 )
Rc Rb
M Rc is the sum of moments corresponding to the development of the
design values of the resisting moments of the columns;
M Rb is the sum of moments corresponding to the development of the
design values of the resisting moments of the partial strength
joints.
The ductile behaviour of the joints is guaranteed by defining an appropriate
hierarchy of resistance for each component. In this respect, with reference to
sagging moments, the end-plate and the column flange under bending as well as
the column web panel in shear have to be considered ductile components;
whereas the concrete slab under compression and the bolts under tension are
assumed to be brittle.
With regard to hogging moments, the steel rebars under tension and, once again,
the end-plate and the column flange under bending, as well as the column web
panel under shear are considered ductile components; while the column web panel
and the beam flanges under compression are assumed to be brittle. Brittle failure
of the bolts in tension before yielding of the end plate and/or of the column flange
can be easily averted by satisfying the following relation:
f
t ≥ 0.36 ⋅d ⋅ ub
( 4.4 )
f
y
where t is the thickness of the end plate or of the column flange; d and fub are the
nominal diameter and ultimate tensile stress of the bolts, respectively; and fy the
yielding stress of the base materials of the considered component (prEN 1993-1,
2000). For the remaining components, we applied the capacity design according to
Table 4.2 and Table 4.3, respectively. It is also necessary to ensure that the joint
possesses adequate resistance and rotational capacity.