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

4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS
For Mechanism 2, assuming an inclination θ = 45° of the concrete struts, we have
that the resistance of a compressed concrete strut, Fccs is equal to:
114
h
F 0.6
c
ccs = νfcd
⋅tslab ⋅ bs ≅ ⋅fcd ⋅tslab ⋅ ( 4.7 )
2
The resistance of the mechanism 2 results the sum of the component of two
compressed struts in the direction of the force transferring in the column.
F
F 2 2 ccs
Rd = ⋅ = 0.6 ⋅fcd ⋅ tslab ⋅ hc
( 4.8 )
2
As Mechanism 2 is not intended to be the dissipative mechanism, an overstrength
factor must be introduced; we must also taken into account the fact that the
concrete resistance νfcd usually considered in Eurocode 2 for compressed struts is
a safe side value. With an overstrength factor of 1.2 we obtain the formula
contained in the current version of the Eurocode 8 (2002):
F = ⋅f ⋅t ⋅ h
( 4.9 )
Rd2 0.7 cd slab c
Because Ft2 is equal for geometry to the resistance FRd2/2, the section As2 of the
steel re-bars into the main beam should comply with:
A
S2
F
≥
2 ⋅ f
Rd2
yd, T
( 4.10 )
These re-bars should be spread in a zone width equal to the dimension of the
column flange as illustrated in Figure 4.11.
Figure 4.11. Re-bars As2 required by mechanism 2