________________________________________________________________________
PROBLEM (7.104) The beam of cross section shown in Fig. 7.103 is to support a moment
Mz = 40 kN m about the z axis. Calculate:
(a) The minimum permissible value of width b.
(b) The minimum allowable value of area As.
Given: ( σs ) all = 150 MPa, (σc )all = 7.5 MPa, d = 500 mm, n = 10
SOLUTION
Referring to Fig. 7.38:
(1 ) (1 ) 1
;,
( ) 7.5 150 10 3
call s
kd d k kd d k k
n
σσ
−−
==
=
(a) The first of Eqs. (7.44):
3
6
max 2
2(40 10 )
() 7.510 11
(0.5) ( )(1 )
39
cb
σ
×
=×=
−
from which
mb 144.0=
(b) The second of Eqs. (7.44):
3
640 10
150 10 1
(0.5)(1 )
9
s
s
A
σ
×
=×=
−
or
2
600 mmAs=
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