Recommended design steps for singlyreinforced sections when beam
dimensions are not known:
Will assume material properties, loads, span lengths and moments are all known.
Usually the beam selfweight is not known, but with some experience you
should be able to make a good estimate of the section dimensions.
The self
weight can be corrected after the final dimensions are established (step 7).
1.
Select a reasonable value for
ρ
, either based on experience or the value
suggested in class,
2.
Calculate the reinforcement index,
ω
=
ρ
f
y
/f
c
'
3.
Calculate the coefficient
R
=
f
c
'
ω
(1  0.59
ω
)
(Reasonable value?
)
4.
Calculate the required value of
b d
2
=
(M
u
/
φ
)/R
; assume
φ
= 0.9
5.
For a typical beam, select
b
as a function of d, i.e.,
b
≅
α
d
, where 0.4
≤
α
≤
0.7.
For some cases where the column width is known, forming costs can
be reduced by setting
b(beam) = b(column)
.
6.
Solve for
d
.
a) If beam width,
b,
is selected as a percentage,
α
, of the effective depth,
d
:
Round
d
to a 0.5 in. value
to get a whole inch
value for
h.
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 Spring '11
 Wight
 10%, steel bars, beam selfweight

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