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I
v
I
v
I
b
Figure 14.7
Floor beam, vertical members, and diagonal members of a pony truss bridge.
Calculate the buckling load as
2
P m P
cr
=
e
14.2.2.3 Case study of pony truss by Timoshenko's method
The following bridge has been considered for the case study:
Length of vertical members = l = 120″
l
= 120″ (3048 mm)
Modulus of elasticity =
E
= 29,000 ksi (199,955 MPa)
Moment of inertia of vertical members =
I
v
= 9.906 mm × 10
7
mm
(238 in
4
)
Length of floor beam =
d
= 6756 mm (266″)
Moment of inertia of floor beam =
I
b
= 1.361 mm × 10
9
mm (3270 in
4
)
Length of diagonal members =
a
= 3810 mm (150″)
Moment of inertia of diagonals =
I
d
= 9.906 mm × 10
7
mm
(238 in
4
)
Length of each panel = 2
c
= 180″ (4572 mm)
Total length of all top chord members =
L
= 29,041 mm (1143.36″)
Moment of inertia of top chord members =
I
t
= 2.219 mm × 10
8
mm
(533 in
4
)
1. Calculate the modulus of equivalent elastic foundation
a. Vertical members
3
l
EI
v
A
=
=
0 0835
.
in/kip
3
2
l d
EI
b
B
=
=
0 025
.
in/kip
2
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