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

4. SEISMIC RESPONSE OF PARTIAL-STRENGTH COMPOSITE JOINTS
where σSd, col is the average normal stress in the panel zone. In the current Draft of
Eurocode 3 (2001), the influence of the normal stress σ due the column axial force
is approximately accounted for by means of a reduction coefficient equal to 0,9. In
particular, the codified value of the reduction factor is on the safe side up to a
column axial load equal to 45% of the column squash load.
After yielding, the rotational stiffness of the web panel zone can be attributed to the
bending of the column flanges. It is computed as:
118
K
pl,1
24 EIfc
= ( 4.16 )
5 t z
fc eq
where Ifc is the inertia moment of the column flanges:
We obtain:
3
c fc
b t
I fc = ( 4.17 )
12
2
,1 1.04 tcf
pl el c
k = ⋅G ⋅ b ⋅ ( 4.18 )
z
eq
If it is assumed that the post-elastic stiffness of the joint Kpl,1 is valid for a range
∆γ = 3γy, the strength Vpl,1 of the joints at an angle of distortion equal to 4γy is then
given:
V = k ⋅ + k ⋅ ( 4.19 )
,1 ,1 3
pl el γ y pl γ y
At an angle of distortion equal to 4γy it is possible to assume that strain hardening
in the web panel in shear begins. The strain hardening branch stiffness Kpl,2 is
suggested as follows:
kpl,2 = Gsh ⋅( hc − tcf ) ⋅ tcw
( 4.20 )
where Gsh is the strain hardening shear modulus that can be assumed equal to Gsh
= 1/100 Gel.
The column web panel must withstand the shear stresses acting when the global
frame mechanism arises, that is, it must support that. In accordance with Eurocode