fundamentals of engineering supplied-reference handbook - Ventech!

BEAMS: homogeneous beams, flexure about x-axis
Flexure – local buckling:
No local buckling if section is compact:
b f 65
2 t
f
≤ and
F
where: For rolled sections, use tabulated values of
y
122
b
f
2t
f
h 640
≤
t F
w
and
For built-up sections, h is clear distance between flanges
For Fy ≤ 50 ksi, all rolled shapes except W6 × 19 are compact.
Flexure – lateral-torsional buckling: Lb = unbraced length
L
p
300ry
=
F
y
LRFD–compact rolled shapes
ry
X 1
2
L r = 1 + 1 + X 2 FL
F
L
where: FL = Fy – 10 ksi
X
1
φ = 0.90
=
φMp = φ Fy Zx
φMr = φ FL Sx
C
b
=
2.
5
π
S
x
EGJA
2
Cw
⎛ Sx
⎞
X 2 = 4 ⎜ ⎟
I ⎝ GJ ⎠
M
max
y
12.
5
+ 3 M
Lb ≤ Lp: φMn = φMp
Lp < Lb ≤ Lr:
M
A
max
2
+ 4 M
B
+ 3 M
⎡
⎛ L
φMn = C ⎢
⎜
b φM
p − ( φM
p − φM
r)
⎢
⎜
⎣
⎝
L
Lb > Lr :
Zx Table
= Cb [φMp − BF (Lb − Lp)] ≤ φMp
C
See Zx Table for BF
2
1
b
r
( ) 2
L /r
− L
− L
p
p
⎞⎤
⎟⎥
⎟
⎠⎥⎦
φCb
S x X1
2 X X 2
φM n =
1 + ≤ φMp
L /r 2
See Beam Design Moments curve
b
y
b
y
Zx Table
W-Shapes
Dimensions
and Properties
Table
L
c
y
h
t w
y
ASD–compact rolled shapes
76b
f
=
F
or
20,
000
( d / A ) F
use smaller
f
y
CIVIL ENGINEERING (continued)
Cb = 1.75 + 1.05(M1 /M2) + 0.3(M1 /M2) 2 ≤ 2.3
M1 is smaller end moment
M1 /M2 is positive for reverse curvature
Ma = S Fb
Lb ≤ Lc: Fb = 0.66 Fy
Lb > Lc:
For:
For:
⎡
2
2 F
⎤
y ( Lb
/ rT
)
Fb = ⎢ −
⎥ ≤ 0.6 Fy
⎢3
1,
530,
000C
⎣
b ⎥
⎦
Fb =
Fb =
170,
000Cb
≤ 0.6 Fy
2
( L / r )
b
b
T
12,000C
L d / A
y
f
b
T
≤ 0.6 Fy
102,
000Cb
Lb
510,
000Cb
< ≤
:
F r F
T
Use larger of (F1-6) and (F1-8)
Lb 510,
000Cb
> :
r F
y
Use larger of (F1-7) and (F1-8)
See Allowable Moments in Beams curve
y
(F1-6)
(F1-7)
(F1-8)