Civil Engineering Reference
In-Depth Information
since
(S
1
)
10
=
56 ft,
NL
=
10, and
xL
=
58
−
56
=
2 ft from
NL
=
10 to
support B
NE
is the last wheel on the span and is equal to
NL
=
10
M
B
L
M
(
NL
−
1
)
,N1
+
P
N1,NE
(xL)
60
M
9,1
+
P
1,10
(xL)
60
R
B
=
=
=
9264
+
304
(
2
)
60
=
=
164.5 kips,
R
B
L
3
R
B
L
3
M
(
NP−1
)
,N1
=
M
3,1
M
C
=
−
−
=
164.5
(
20
)
−
960
=
2331 ft-kips.
The superstructure loaded with transverse floorbeams has a 100
[
1
−
(
2331
/
2536
)
]=
8.1% decrease in bending moment with
NP
=
4 at the location
of maximum moment.
With
NP
=
13 (Cooper's load configuration wheel number 13)
From
Table 5.1:
With
NP
=
13, the first wheel on the span
=
N1
=
10
x
1
=
(S
1
)
13
−
(S
1
)
10
=
74
−
56
=
18 ft
support B is 40
+
18
=
58 ft from N1
=
10
13, the last wheel on the span,
NL
, is the end of 5 ft of the
uniform load,
w
xL
With
NP
=
=
(
2
L/
3
)
−[
(S
1
)
w
−
(S
1
)
13
]=
40
−
(
104
+
5
−
74
)
=
5 ft from the begin-
ning of the uniform load,
w
, to support B
NE
is the last wheel on the span and is equal to 5 ft of the uniform load,
w
M
18,10
+
P
10,w
(xL)
60
M
B
L
8412
+[
(
284
)(
5
)
+
4
(
5
)(
5
/
2
)
]
R
B
=
=
=
60
=
164.7 kips,
R
B
L
3
M
12,10
=
M
C
=
−
164.7
(
20
)
−
960
=
2334 ft-kips.
The superstructure with transverse floorbeams has a 100
[
1
−
(
2334
/
2588
)
]=
9.8% decrease in bending moment with
NP
=
13 at the loca-
tion of maximum moment.
5.2.1.2
Influence Lines for Maximum Effects of Moving Loads on
Statically Determinate Superstructures
Influence lines facilitate both the appropriate placement of loads and determination of
maximum effects in steel beam and girder superstructures (shear forces and bending
moments), trusses (axial forces), and arches (axial forces, shear forces, and bending
moments). Influence lines may be constructed for moving load analysis of statically
determinate superstructures by moving a unit concentrated load across the super-
structure and determining the value of an effect at each location. The construction of
