Civil Engineering Reference
In-Depth Information
Note:
All shear and negative moment values are at face of supporting beams.
V
u
@ exterior columns
= 6.4(28.58)/2 = 91.5 kips
V
u
@ first interior columns
= 1.15(91.5) = 105.3 kips
V
u
@ interior columns
= 6.4(28.5)/2 = 91.2 kips
-M
u
@ exterior columns
= 6.4(28.58)
2
/16 = 326.7 ft-kips
+M
u
@ end spans
= 6.4(28.58)
2
/14 = 373.4 ft-kips
-M
u
@ first interior columns
= 6.4(28.58)
2
/10 = 522.8 ft-kips
+M
u
@ interior span
= 6.4(28.50)
2
/16 = 324.9 ft-kips
(3)
Design of the column line beams also includes consideration of moments and shears due to wind.
The wind load analysis for Building #1 is summarized in Fig. 2-13.
Note: The reduced load factor (0.5) permitted for load combinations including the wind effect
(ACI 9-3 and 9-4) is in most cases, sufficient to accommodate the wind forces and moments without
an increase in the required beam size or reinforcement (i.e., the load combination for gravity load only
will usually govern for proportioning the beam).
(4)
Check beam size for moment strength
Preliminary beam size = 19.5 in.
36 in.
For negative moment section:
20M
u
d
2
20(522.8)
17
2
b
w
=
=
=
36.2 in.
>
36 in.
where d = 19.5 - 2.5 = 17.0 in. = 1.42 ft
For positive moment section:
b
w
= 20 (373.4)/17
2
= 25.8 in. < 36 in.
Check minimum size permitted with
ρ
= 0.0206:
b
w
= 14.6(522.8)/17
2
= 26.4 in. < 36 in. O.K.
Use 36 in. wide beam and provide slightly higher percentage of reinforcement (
ρ
> 0.5
ρ
max
) at
interior columns.
Check for fire resistance: from Table 10-4, required cover for fire resistance rating of 4 hours or less
=
3
⁄
4
in. < provided cover. O.K.
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