Like
their masonry counterparts, arched trusses are extremely stable. As
many as three |
flexible
hinge points, or fractures, can develop in the structure without it
failing. In fact, |
some
arch trusses are specifically designed to have one, two, or three hinge
points in order |
to
relieve the build up of stresses in the arch. This allows it to
conform more readily to |
changes
in its shape induced by temperature fluctuations or asymmetrical loads. |
. |
 |
 |
 |
click image to enlarge |
a) singly hinged |
b) doubly hinged |
c) triply hinged |
. |
Fig. 184 - Single, double, and triple hinged
arched trusses
(static demonstration models) |
|
. |
Cantilever bridge |
. |
Another
solution to the problem that most of the dead weight of the deck is
concentrated |
mid-span, is to cantilever the roadbed either from the end abutments or
from a support that |
is
located center span. Cantilevering the deck from the end abutments
entails extending a |
diagonal
bracing strut from the abutment to a point near the mid-point of the deck.
The |
downward
compressive stresses exerted by the deck load are displaced down the
struts to |
the
ground. |
. |
 |
Fig. 185 - Cantilever bridge |
 |
supported by end abutments |
◄ (static demonstration
model) |
(scale visualization model)
► |
|
click image to enlarge |
|
. |
A deck
that is cantilevered from a central support extends outwards
in both directions in a |
balanced fashion like the limbs of a tree.
This centers the mass of the structure over the |
support rather than in the middle of the span. A
bending moment force applied to one end |
of the dual-cantilever is countered by the moment exerted by
the weight of the other end, |
like two masses being weighed on a balance scale. |
. |
 |
Fig. 186 - Centrally |
 |
supported cantilever |
bridge |
◄(static demonstration model) |
(training aid model) ► |
click image to enlarge |
|
. |
Back
to Knowhere |
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Page 113
- Building stability - Cantilever bridge |
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