Approximate and refined analysis methods - Computational Analysis and Design of Bridge Structures - page 54

and tower in this case have to be analyzed as a beam column. The stiff-
ness of the girder has less effect on the vertical deflection of the girder
system. However, the towers are the most critical components of the system
because the second-order moments may cause formation of a mechanism
(plastic hinges) in a tower. Another aspect of nonlinearity is due to large
displacements of the structure. Because it affects the stresses, the principle
of superposition does not apply, and the problem has to be treated by the
large displacement theory (or so-called second-order theory). The iteration
process keeps modifying the geometry and maintaining the equilibrium of
the system.

2.5.9 Suspension bridge
Structural analysis of suspension bridge is usually made for the combina-
tion of dead load, live load with impact, traction and bracing, temperature
changes, settlement of supports, and wind (both static and dynamic effects).
Figure 2.39 shows suspension bridge models with different arrangements.
In the early stages of development of the theory for the suspension bridge,
elastic theory was used for the analysis. The suspension bridges were ana-
lyzed by the classical theory of structures, the so-called elastic (also known
as first-order) theory of indeterminate analysis that ignores deformation of
the structure. The elastic theory can be simply expressed as

M M hy

′ −

= (2.15)

Cable

Tower

Stiffening truss

(a) (b)

Ties

(c) (d)

(e)
Figure 2.39 Suspension bridge model with different arrangements: (a) one suspended
span with pinned stiffened truss; (b) three suspended spans with pin-ended
stiffened trusses; (c) three suspended spans with continuous stiffened
trusses; (d) multisuspended spans with pin-ended stiffened trusses; (e) self-
anchored suspension bridge.