Civil Engineering Reference
In-Depth Information
From Equation 5.31,
α
M
M
y,Rd
=
0.9
×
125
=
113 kN m
(5.52)
This exceeds
M
y,Ed
, so this column length has sufficient major-axis
resistance. It can be shown that although the length above has a higher
end moment, 30 kN m, it also is strong enough, because it is in double-
curvature bending.
5.7.4
Resistance of the column length, for minor-axis bending
The margin of resistance to major-axis bending (above) is quite low, so
two more T16 reinforcing bars were added to the cross-section, as shown
in Fig. 5.18(a), to increase minor-axis resistance.
The cross-sectional areas given in Section 5.7.2 now become:
A
a
=
6640 mm
2
A
s
=
1206 mm
2
A
c
=
94 550 mm
2
and
N
pl,Rd
is increased from 4052 kN to 4224 kN.
The second moments of area are:
for the steel section, from tables, 10
−6
I
a
=
17.7 mm
4
for the reinforcement, 10
−6
I
s
=
1206
×
0.115
2
=
15.9 mm
4
for the concrete, 10
−6
I
c
=
320
2
×
0.32
2
/12
−
17.7
−
15.9
=
840 mm
4
With
E
c,eff
=
10.8 kN/mm
2
(Section 5.7.2), and from Equation 5.22,
10
−12
(
EI
)
eff,II
=
0.9(0.21
×
17.7
+
0.20
×
15.9
+
0.5
×
0.0108
×
840)
=
10.3 N mm
2
Figure 5.18
Interaction diagram for minor-axis bending of external
column
