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Pe1y2EIy
K1L22EIy
KyL2229000116
12 1221601 kips
B1yCmy
6.6-13
(a) LRFD solution:
2. 5Mmax 3MA4MB3MC
12. 54Q
2. 54Q3044Q301. 923
For Cb1. 923,
bMn1. 923331636. 5 ft-kips bMp600 ft-kips
∴use bMnbMp600 ft-kips
Pu
8
Mux
Muy
0. 7769 8
4. 096Q
Let 0. 7769 8
9
600 01, Solution is: 36. 77 kips
Maximum Q36. 8 kips
2. 5Mmax 3MA4MB3MC
12. 52. 5Q
2. 52. 5Q3042. 5Q301. 923
For Cb1. 923,
Mn
b
1. 923220423. 1 ft-kips Mp
b
399 ft-kips
Pa
8
Max
May
0. 7803 8
2. 563Q
Let 0. 7803 8
2. 563Q
6.7-1
Determine the axial compressive design strength. Use LcKxLfor the unbraced
2. 5Mmax 3MA4MB3MC
12. 5135. 7
2. 5135. 7335. 11421. 83378. 772. 208
For Cb2. 208, bMn2. 2084791058 ft-kips
Pu
8
Mux
Muy
0. 5182 8
135. 7
6.7-2
(a) LRFD solution
M2
98. 4 0. 266 7
For the braced case,
Pe12EIx
2. 598. 4336. 948. 20353. 32. 239
For Cb2. 239, bMn2. 239415929. 2 ft-kips
Since 929.2 ft-kips bMp,usebMnbMp473 ft-kips
Pu
528
Pu
cPn
8
9
Mux
bMnx
Muy
bMny
0. 8341 8
9
98. 4
473 0
b
Since 618.0 ft-kips Mp
b
,use Mn
b
Mp
b
314 ft-kips
Pa
360
6.8-1
(a) LRFD solution
The factored axial load is
Pu1. 20. 30 2361. 60. 70 236349. 3 kips
Pu
cPn
8
9
Mux
bMnx
Muy
bMny
0. 7308 8
9
248. 6
258 0
Pu
cPn
8
9
Mux
bMnx
Muy
bMny
0. 4318 8
9
248. 6
422 00. 955 4
0. 955 1. 0 (OK)
Calculate B1:
is not needed.)
UseaW1279
selection.
Mnx
281 ft-kips and Pn
538 kips
Pn/c
538 0. 438 7 0. 2 ∴use Equation 6.5 (AISC Eq. H1-1a):
Pa
Pn/c
8
9
Max
Mnx/b
May
Mny/b
0. 4387 8
9
168
281 0
0. 970 1. 0 (OK)
6.8-2
Mux (top) 182 ft-kips
Pu
400
6.8-3
(a) LRFD Solution
Mntx 1
As a preliminary check (remember that Cbhas not been accounted for)
Pu
Mux
Muy
0. 1918 135
Cb
bMn1. 14157179. 0 ft-kips bMp176 ft-kip
∴use bMn176 ft-kips
Pu
2cPn
Mux
bMnx
Muy
bMny
0. 1918 138. 2
176 0
Pn/c234 kips Mnx/b104 ft-kips
As a preliminary check (remember that B1has not yet been computed and Cbhas not
been accounted for),
Pa
Pn/c
45
234 0. 192 3 0. 2 ∴use Equation 6.6 (AISC Equation H1-1b)
Pa
Max
May
45
Pe1x
2885
Max B1xMntx 1. 0269092. 34 ft-kips
From Figure 5.15 in the textbook, Cb1. 14. Modify Mnx/bto account for Cb.
6.8-4
Pu140 kips
The factored moments at the top are
Mntx Mnty 150 ft-kips
The factored moments at the bottom are
As a preliminary check (remember that Cbhas not been accounted for)
Pu
2cPn
Mux
bMnx
Muy
bMny
140
21020150
525 150
260 0. 931
0. 931 1. 0 (OK)
[6-33]
© 2018 Cengage Learning®. All Rights Reserved. May not be scanned, copied or duplicated,
or posted to a publicly accessible website, in whole or in part.
bMnx 568 ft-kips, cPn979 kips, and bMny 273 ft-kips
Determine which interaction equation to use:
Pu
cPn
140
979 0. 143 0. 2 ∴use Equation 6.4 (AISC Eq. H1-1b):
As a preliminary check,
Pu
Mux
Muy
140
B1xCmx
1−Pu
Pe1x
0. 4
1−140
7756
0. 407 1.0 ∴B1x1. 0 as assumed
Pe1y2EIy
6.8-5
(a) LRFD Solution
Pu1. 21351. 6415826. 0 kips
The factored moments are
Mntx (top) 1. 2901. 6270540. 0 ft-kips
Pu
cPn
8
9
Mux
bMnx
Muy
bMny
826
1620 8
9
540
1030 0
0. 976 1/0 (OK)
Calculate B1for the axis of bending:
[6-35]
© 2018 Cengage Learning®. All Rights Reserved. May not be scanned, copied or duplicated,
or posted to a publicly accessible website, in whole or in part.
(Since this shape is adequate for Cb1.0, computation of the actual value of Cbis not
necessary.)
UseaW14159
(b) ASD Solution
been accounted for),
Pa
Pn/c
550
1070 0. 514 0. 2 ∴use Equation 6.5 (AISC Equation H1-1a)
Pa
8
Max
May
0. 514 8
360
Pn/c
9
Mnx/b
Mny/b
9
618 01. 08
Calculate B1:
[6-36]
© 2018 Cengage Learning®. All Rights Reserved. May not be scanned, copied or duplicated,
or posted to a publicly accessible website, in whole or in part.
Cmx 0. 6 −0. 4 M1
M2
0. 6 −0. 4 120
360 0. 466 7
2. 536030412032402. 143
CbMnx/b2. 1436181324 ft-kips Mpx/b649 ft-kips
∴use Mnx/b649 ft-kips
6.8-6
(a) LRFD Solution
Mntx 1. 2160/21. 6160/2224. 0 ft-kips
bMnx 461 ft-kips cPn898 kips bMny 229 ft-kips
Determine which interaction equation to use:
Pu
cPn
128. 8
898 0. 143 4 0. 2 ∴use Equation 6.4 (AISC Eq. H1-1b):
As a preliminary check (remember that Cbhas not been accounted for)
Pu
Mux
Muy
128. 8
Check the W14s. Try a W14 82. From Table 6-2,
bMnx 462 ft-kips cPn697 kips bMny 168 ft-kips
Pu
cPn
128. 8
697 0. 184 8 0. 2 ∴use Equation 6.4 (AISC Eq. H1-1b):
Pu
Mux
Muy
128. 8
M2
299. 6 0. 300 9
Cmy 0. 6 −0. 4 M1
M2
0. 6 −0. 4 33. 6
43. 4 0. 290 3
Pe1x2EIx
Lcx22EIx
KxL2229000662
0. 8 16 1228031 kips
2. 5299. 6393. 1437. 83168. 72. 222
∴use bMn446 ft-kips
Pu
128. 8
The service-load moments at the bottom are
Mntx 214 ft-kips, Mnty 31 ft-kips
selection. For the two axes,
Max B1xMntx 1. 0214214 ft-kips
Check the W12s. Try a W12 79. From Table 6-2,
Mnx/Ωb277 ft-kips Pn/Ωc520 kips Mny/Ωb135 ft-kips
As a preliminary check (remember that B1has not yet been computed and Cbhas not
been accounted for),
Pa
92
Cmx 0. 6 −0. 4 M1
M2
0. 6 −0. 4 160
214 0. 300 9
Cmy 0. 6 −0. 4 M1
M2
0. 6 −0. 4 24
31 0. 290 3
Pe1x2EIx
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