S6S211
© Canadian Standards Association
10.9.5.5 Bending resistance
The factored bending resistance, Mrc, of a composite concretefilled hollow structural section shall be taken as
Mr c = Cre + Cr’e’
where
(a) for a rectangular hollow structural section:
Cr =
Cr’ = [f066][f020][f020]c a(b – 2t) fc’ Cr + Cr’ = Tr
= [f066][f020][f020]
s[f020][f020]Ast Fy
Note: The concrete in compression is taken to have a rectangular stress block of intensity fc ’ over a depth of a = 0.85c, where c is the depth of concrete in compression.
(b) for a circular hollow structural section:
Cr =
e =
Cr’ =
e ‘ =
where
[f062] = value in radians derived from the following recursive equation:
bc = D sin([f062][f020][f020]/2)
a = bc /2 tan([f062][f020][f020]/4)
Conservatively, Mr c may be taken as
[f044]
fs s y r
A F C
 ’
2
f b
s y
F Dt 2
bc 1
2 1
p 
[23a1] ( ) + [23a3]
[23a2]
b b
[23a4]
[23a6] [23a5]
2
8 2 2
f b
c c
f D b D a
’ [23a1] [23a3][23a2]
[23a1]
[23a3] [23a2]
– –
[23a4] [23a6][23a5]
[23a4]
[23a6] [23a5]
c
b
2
b
c
[23a1]
[23a3] [23a2] [23a2]
p – b b
( ) + – 
1
2 1 5 6 0 5
[23a4]
[23a6] [23a5] [23a5]
. .
D b D a
2
c c
( )
A F D f
D
f f b b b
f
0 25
2
2
s s y c c
+ ’ ( ) – ( ) ( )
[23a1][23a3]
2 2 4
0 125
b
=
. sin / sin / tan /
.
2 ’ +
f DtF
c s y
[23a4][23a6]
c
f
Mr c =
( ) + ( ) 
Z th F

2 2 3 0 5 0 5
2
f
/ . .
2
n s y
[23a1][23a3]
( ) – 
D t D t h f
3
( )
n c c
[23a4][23a6] ’
f
where
hn =
Z = plastic modulus of the steel section alone
f
A f
D f t F f
c c c
c c c y c c
’
’ + – ’
2 4 2
f f f
( )
October 2011
454
(Replaces p. 454, May 2010)
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