Civil Engineering Reference
In-Depth Information
8
7
6
5
4
m
= 1
m
= 2
m
= 3
m
= 4
3
2
1
0
0
0.5
1
1.5
2
2.5
a
/
b
3
3.5
4
4.5
5
Figure 14.5
Buckling stress coefficients for uniaxially compressed plate. (Data from Ryall, M.J.
et al.,
Manual of Bridge Engineering
, Thomas Telford Publishing, London, 2000.)
In this chapter, the pony truss, a half-through bridge truss that has its
deck between the top and bottom chords and has no top lateral bracing, is
used as an example. A pony truss can be idealized as a continuous beam
with intermittent spring support (Figure 14.6). The stiffness of these spring
supports will depend on the vertical and diagonal members of the truss and
floor beams. A method for solving the buckling of a continuous beam on
elastic foundation was suggested by Timoshenko (1936).
Many classical methods were developed for solving the buckling problem,
but most of them are based on the idealization of a bridge as a continuous
beam on elastic foundation. In this chapter, the method of finding a buckling
load of a pony truss bridge as suggested by Timoshenko (1936) is illustrated.
Another effective method, which gave comparable results but is not listed here,
was established by the Structural Stability Research Council (SSRC) Guide
(Galambos 1998). A case study of a 27-m (90′) pony truss is considered, and
the results are compared with those based on an ANSYS numerical model.
Figure 14.6
Pony truss idealized as a continuous beam on spring support.
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