Civil Engineering Reference
In-Depth Information
0.90 (subsequent check after detailing bolted connec-
tions should be made),
Assume that
n
ng
=
201,100 in.
4
I
n
∼
0.90
(
223,444
)
∼
201,100
45
4469 in.
3
S
n
≈
∼
26.4 ksi
< F
tall
<
0.55
(
50
)<
27.5 ksi OK (a subse-
quent check of assumed dead load after final proportioning and detailing
should be made).
Fora90 ftlongplategirder,designfor
>
2,000,000cycleswithameanimpact
percentage of 35% of the maximum impact.
Δσ
max
∼
σ
tmax
∼
9814
(
12
)/
4469
=
16.2 ksi. Therefore, details with a fatigue detail
less than Category B (allowable fatigue stress range
6032
(
12
)/
4469
=
=
16 ksi) should not be
used near the bottom flange area of the span.
τ
max
=
9.15 ksi
< F
rail
<
0.35
(
50
)<
17.5 ksi OK.
Equation 7.24 yields the maximum unsupported length as
486
/(
85
)(
5
/
8
)
=
2
(
6.3
)
π
L
r
y
2
(
29,000
)
(
50
)
2
max
≤
≤
38.0
≤
(
38.0
)(
4.67
)
=
177 in.
=
14.75 ft (AREMA, 2008 recommends a maximum of
L
12 ft),
144
4.67
2
0.55
(
50
)
2
6.3
F
call
=
0.55
(
50
)
−
=
27.5
−
0.73
=
26.8 ksi
2
(
29,000
)
π
23.7 ksi OK.
The girder will be laterally supported (after erection) by brace frames at a
maximum spacing of 12 ft.
>
σ
cmax
>
9814
(
12
)/
4965
=
Girder design (for fabrication and erection loads)
:
During fabrication and erection the entire girder may be laterally unsup-
ported. Itisassumedthaterectionliftswillnotbedonecoincidentwithwindy
conditions.
girder self-weight
∼
1.15
(
521
)
∼
600 lb/ft (with 15% contingency load),
0.6
(
90
)
2
/
8
σ
girder
=[
]
(
12
)/
4469
=
1.6 ksi
using an allowable bending stress of 1.25
(
0.55
)F
y
=
0.69
F
y
(see Table 4.5),
L
r
y
0.69
(
50
)
−
1.6
girder
=
2
(
29,000
)
=
185,
0.69
(
50
)
2
/6.3
π
and the maximum unsupported length for fabrication and erection is
L
=
4.67
(
185
)/
12
=
72.1 ft (80% of girder length) using a basic allowable stress of
1.25
[
0.55
F
y
]
.
