Civil Engineering Reference
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12.3 Behavior of SuSpenSion BridgeS
As the flexible cables are the main structural component carrying dead
loads and live loads and the span length is longer than most other types of
bridge, the global vertical stiffness of a suspension bridge is very low. The
principles and characteristics of suspension bridges are distinguished from
others. Due to the flexible cables and its huge deflections from the very
beginning of construction to the stage of operations, the geometry con-
figuration of a suspension bridge can no longer be treated as constant. The
changes of geometry configuration, hence the construction procedures, are
deeply involved and crucial in the design and analyses. Obviously, geomet-
ric nonlinear analysis is the basis of the structural analysis of suspension
bridges.
12.3.1 Basis of cable structures—initial
stress and large displacements
Taking a simple symmetric truss structure as shown in Figure 12.10 as
an example, tension in truss elements under external load can simply be
obtained from the force balance equation at node B as
PL
H
(12.1)
T
=
2
The strain of the truss element is obtained as
PL
EAH
(12.2)
ε =
2
where
E
and
A
are the Young's modulus and cross area of the truss element,
respectively.
C
A
L
T
T
H
L
L
1
B
d
P
Figure 12.10
A simple symmetric truss structure.
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