Analysis and modelling of the seismic behaviour of high ... - Ingegneria
Analysis and modelling of the seismic behaviour of high ... - Ingegneria
Analysis and modelling of the seismic behaviour of high ... - Ingegneria
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5. SEISMIC BEHAVIOUR OF RC COLUMNS EMBEDDING STEEL PROFILES<br />
Shear area calculated on <strong>the</strong> basis <strong>of</strong> <strong>the</strong> length jh, used to regulate <strong>the</strong> effective<br />
length <strong>of</strong> <strong>the</strong> web panel <strong>and</strong> <strong>the</strong> distance between vertical resultant forces coupled<br />
in <strong>the</strong> compression strut. It is proposed to use a fixed value <strong>of</strong> jh = 0.8ds based on<br />
comparison with test data.<br />
Moreover, experimental tests have demonstrated that <strong>the</strong> panel zone is able to<br />
provide a significant post-yield resistance (Krawinkler, 1978). When <strong>the</strong> panel zone<br />
has uniformly reached yielding, an additional increase in shear strength ∆Vj,wps can<br />
be attributed to <strong>the</strong> resistance in flexion <strong>of</strong> <strong>the</strong> elements surrounding <strong>the</strong> panel.<br />
This resistance can be approximated by springs at <strong>the</strong> four corners whose stiffness<br />
is that corresponding to rotations <strong>of</strong> <strong>the</strong> column flanges concentrated at each<br />
corner. When <strong>the</strong> boundaries <strong>of</strong> <strong>the</strong> panel zone are assumed to be rigid, <strong>the</strong> post-<br />
elastic stiffness <strong>of</strong> <strong>the</strong> joint, attributable to <strong>the</strong> four springs, is computed as:<br />
∆ V = min<br />
200<br />
j, wps<br />
4⋅ M 4⋅<br />
1 b t f<br />
4<br />
b t f<br />
= =<br />
d d d<br />
2 2<br />
Pl, cf , Rd cf cf ym, d , cf cf cf ym, d , cf<br />
s s s<br />
2⋅ M + 2⋅<br />
M b t f + b t f<br />
=<br />
d 2⋅<br />
d<br />
2 2<br />
Pl, cf , Rd Pl, st, Rd cf cf ym, d , cf p sp ym, d , s<br />
s s<br />
( 5.23 )<br />
Where <strong>the</strong> steel column web is encased in concrete <strong>the</strong> design shear resistance <strong>of</strong><br />
<strong>the</strong> panel may be increased with <strong>the</strong> contribution <strong>of</strong> <strong>the</strong> inner concrete strut Vccs,<br />
that is <strong>the</strong> design shear resistance <strong>of</strong> <strong>the</strong> concrete encasement to <strong>the</strong> web panel.<br />
The concrete compression strut, shown in Figure 5.15b, is similar to <strong>the</strong><br />
mechanism used to model shear in a reinforced concrete connection. In composite<br />
connections, <strong>the</strong> concrete compression strut could be mobilized in resisting <strong>the</strong><br />
connection shear ei<strong>the</strong>r due to <strong>the</strong> presence <strong>of</strong> <strong>the</strong> horizontal stiffener plates<br />
welded to <strong>the</strong> column or due to <strong>the</strong> friction <strong>and</strong> <strong>the</strong> flexural forces acting in <strong>the</strong> steel<br />
column flange. In case <strong>of</strong> presence <strong>of</strong> <strong>the</strong> stiffener plates, <strong>the</strong> location <strong>and</strong> width <strong>of</strong><br />
<strong>the</strong>se determine how effectively <strong>the</strong> concrete strut is mobilized. The shear<br />
resistance <strong>and</strong> <strong>the</strong> moment resistance for <strong>the</strong> concrete compression strut are<br />
calculated as follows:<br />
1 1 0.85⋅<br />
f<br />
V = ⋅ν ⋅ f ' ⋅ A ⋅ senθ = ⋅ν ⋅ ⋅ A ⋅ senθ<br />
( 5.24)<br />
ck<br />
j, ccs<br />
1.3<br />
cd c<br />
1.3 γ c<br />
c<br />
( )<br />
M = V ⋅ ⋅ d<br />
( 5.25 )<br />
Rd , j, ccs j, ccs 0.8 s