Civil Engineering Reference
In-Depth Information
Figure 5.16
Interaction diagram for major-axis bending of external
column
The bending resistance at point D, with
W
pc
halved to allow for cracking, is
M
max,Rd
=
W
pa
f
yd
+
W
ps
f
sd
+
0.85
W
pc
f
cd
/2
=
0.568
×
355
+
0.0925
×
435
+
7.53
×
14.2/2
=
295 kN m
(5.47)
When the plastic neutral axis moves from D-D to C-C, the axial
compression changes from
N
pm,Rd
/2 to
N
pm,Rd
, because the changes in axial
force are of the same size (but of opposite sign) as when it moves from
D-D to B-B.
When the plastic neutral axis moves from B-B to C-C, the resultant of
all the changes in axial force passes through G (from symmetry), so that
the bending resistances at points B and C are the same, and are
M
pl,Rd
=
M
max,Rd
−
W
pa,n
f
yd
−
W
pc,n .
f
cd
/2
=
295
−
0.036
×
355
−
1.4
×
14.2/2
=
272 kN m
(5.48)
The axial force at point C is
N
pm,Rd
=
1346 kN
(5.49)
so the position of line AC in Fig. 5.11 is as shown in Fig. 5.16.
5.7.3
Resistance of the column length, for major-axis bending
The design axial compression is
N
Ed
=
2807 kN from Equation 5.40; and
from Equation 5.44:
N
cr,eff
=
π
2
×
15.8
×
1000/4
2
=
9750 kN
