Civil Engineering Reference
In-Depth Information
Design for flexure:
Check beam size for moment strength
Preliminary beam size = 19.5 in.
36 in.
For negative moment section:
(
)
20M
u
d
2
20 586.6
b
w
=
=
=
40.6 in.
>
36 in.
17
2
where d = 19.5 - 2.5 = 17.0 in. = 1.42 ft
For positive moment section:
b
w
= 20 (375.7)/17
2
= 26.0 in. < 36 in.
Check minimum size permitted with:
b
w
= 14.6(586.6)/17
2
= 29.6 in. < 36 in. O.K.
Use 36 in. wide beam and provide slightly higher percentage of reinforcement at interior columns.
Top reinforcement at interior support:
M
u
426.2
417
A
s
=
4d
=
()
= 6.27 in.
2
From Table 3-5: Use 9-No. 9 bars (A
s
= 9.0 in.
2
)
Check
ρ
= A
s
/bd = 9.0/(36
17) = 0.0147 >
ρ
min
= 0.0033
O.K.
Top reinforcement at exterior support:
A
s
= 375.7/4(17) = 5.53 in.
2
From Table 3-5: Use 7-No. 9 bars (A
s
= 7.0 in.
2
)
Check
ρ
= A
s
/bd = 7.0/(36
17) = 0.0114 >
ρ
min
= 0.0033
O.K
Bottom bars:
A
s
= 375.7/4(17) = 5.53 in.
2
Use 8-No. 8 bars (A
s
= 6.32 in.
2
)
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