# Note: Live load reduction can be applied in accordance with ASCE 7-02 section 4.8.1 (see ASCE 7-02 Eq. 4-1)

Urban and Civil

Nov 25, 2013 (4 years and 5 months ago)

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PROJECT: STEEL BUILDING DESIGN CASE STUDY
SUBJECT: GIRDER SELECTION (30x36 BAYS - BAY STUDY)
(OPTION I)
INTERIOR FLOOR GIRDER SELECTION LIVE LOAD REDUCTION CHECK - Bay Width = 30 ft.
INTERIOR FLOOR GIRDER
Total Bay length =
36 (ft)
Beam Fy =
50 (ksi)
Typical Bay DL = 59.0
(lb/ft
2
)
Assumptions LL = 80.0
(lb/ft
2
)
#1 - Laterally Supported Tributary Width =
30 (ft)
#2 - Compact Sections Tributary Area (A
T
) =
1080.0
(ft
2
)
36 x 30 ft Bays
K
LL
(ASCE-7 02 Table 4-2)=
2.0
36
A
T
* K
LL
=
2160.0
A
T
* K
LL
> 400 ft
2
?
YES
Note: Live load reduction can be applied in accordance with ASCE 7-02 section 4.8.1
(see ASCE 7-02 Eq. 4-1)
L = L
o
*(0.25+15/(K
LL
A
T
)^0.5) ASCE 7-02 Eq. 4-1
L = 46
L = reduced design live load value in psf
L
o
= unreduced live load in psf
A
I
= Tributary area
WDL =
WLL =
Now, calculate a new value for W
u
using the reduced live load as shown above
W
u
= [1.2*dead load + 1.6* reduced live load]
W
u
= 4.32 klf
SHEET 19 of 131
Tributary Width
Red font indicates user input
1770 Lb/ft
1375 Lb/ft
30 30
PROJECT: STEEL BUILDING DESIGN CASE STUDY
SUBJECT: GIRDER SELECTION (30x36 BAYS - BAY STUDY)
(OPTION 1)
INTERIOR FLOOR GIRDER SELECTION (METHOD 1: Explicit Calculations)- Bay Width = 30 ft.
INTERIOR FLOOR GIRDER
Total Bay Length =
36 (ft)
Beam Fy =
50 (ksi)
Typical Bay DL = 59.0
(lb/ft
2
)
Assumptions
LL (LL Reduction is applied) =
45.8
(lb/ft
2
)
#1 - Laterally Supported Tributary Width =
30 (ft)
#2 - Compact Sections
W
DL
=
1770.0 (lb/ft)
36 x 30 ft Bays
W
LL
=
1374.6 (lb/ft)
36
Factored Load - Wu =
4.3 (k/ft)
Factored Max. Moment (Mu) =
700.4 (k-ft)
SELECT SECTION
Use Zx Tables 5-3
φ
⁍渠㴠
φ
⁍瀠㴠婸‪
φ

ㄸ㘮㜷
⡩(
3
)
W24x7
6
Beam Weight (k/ft) 0.076
< 85 plf assumed,don't add Wt.
Mu = 700.4 (k-ft)
φ
䵰‽
㜵7 ⡫ⵦ琩
OK
φ
䵰‾⁍甠M
CHECK LOCAL CONDITIONS
b
f
/ 2 t
f
(LRFD p.1-16) =
6.61
λp = 65 / Fy
.5
=
9.2
OK
λ

f
⼲/
f

CHECK WEB
h / tw (LRFD p.1-16) = 49
λp = 640 / Fy
.5
=
90.5
OK
λ

CHECK SHEAR CAPACITY
Vu = Wu L / 2 = 77.8
φVn = φ
v
(0.6 F
yw
) A
w
=
283.9

v
= .9)
A
w
= d * t
w
(LRFD p.1-16) =
10.5
d =
OK
φ
V

LIVE LOAD DEFLECTION CHECK
∆ = L / 360 =
1.200 (in) - LIMIT
∆ = (5*w
LL
*L
4
)/(384*E*I) =
0.853
(in) - ∆
LL
I (moment of inertia about x-x axis, LRFD p.5-46)=
2100
(in
4
)
OK

‾ ∆
LL
?
SECTION OK
Cost Per Ton
a
1950 (\$)
Total Weight 1.368 (tons)
Total Cost
\$2,667.60
a - costs per ton in place obtained from local fabricator
SHEET 20 of 131
LRFD p.5-46 - Choose
Red font indicates user input
0.4
tw =
24
30 30
Zx
required
= Mu / φ Fy =
Tributary width
PROJECT: STEEL BUILDING DESIGN CASE STUDY
SUBJECT: GIRDER SELECTION (30x36 BAYS - BAY STUDY)
(OPTION 1)
INTERIOR FLOOR GIRDER SELECTION (METHOD 2: Beam Design Tables)- Bay Width = 30 ft.
Beam Design Tables in LRFD
Mu = 700.4 k-ft
Fy = 50 ksi
LRFD Table 5-3 p.5-46
Member
φ
䵰 欭晴⤽

W24x7
6
750
Lightest member for most economical design
Choose W24x76
BEAM CAPACITY CHEC
K
Member W24x7
6
Fy = 50 ksi
LRFD Table 5-3 p.5-46 Zx = 200
in
3
φ
䵮†M 婸‪Z
φ

φ
=
〮0
φ
Mn = 750 k-ft
SHEET 21 of 131
Red font indicates user input