Cable-stayed bridges - Computational Analysis and Design of Bridge Structures - page 361

When any of the followings is of interest, each cable needs to be
modeled as many truss elements with a density of 5-10 m, as shown in
Figure 11.20.
1. Sag itself or a more accurate effect of it
2. Crossties have to be simulated
3. Local natural modes of cables
If this detailed model is elected, the initial stress in cable and/or large dis-
placements have to be considered. Otherwise, the analysis will fail due to
no stiffness attached to each internal nodes of a cable in its perpendicular
direction. When large displacements are considered, loads will be loaded
incrementally and the element's full stiffness will be automatically com-
puted at each iteration step.
Figure 11.20 is an example that shows local natural modes are required
for wind-raining oscillation study. In such a detailed dynamic mode analy-
sis, initial stresses of all cables are obtained separately from an ideal state
analysis and are entered as known parameters to the dynamic mode analy-
sis model.
When cable stays are cradled through pylons, which are rarely used
nowadays, the cradling point can be treated as an anchor point, thus elimi-
nating the need to simulate the possible relative movements between the
stays and the saddles. The fraction between them is large enough to bal-
ance the difference of cable forces between the two sides of the pylon.
However, extreme cable forces due to live loads should be investigated
case by case.
11.5 illustrated exaMPle of sutong Bridge,
Jiangsu, PeoPle's rePuBliC of China
Sutong Bridge crosses Yangtze River about 100 km upstream from
Shanghai. It connects Suzhou and Nantong, two major cities in Yangtze
River Delta area. The bridge name, Sutong, comes from the combination
of these two cites' names and was built in 2008. Its once-world-record-
breaking main span length, 1088 m, made it one of the most famous
long-span cable-stayed bridges. Technically, the motivation of building
such a long-span cable-stayed bridge comes from a feasibility study of
building a cable-stayed bridge with a main span over 1200 m (3937′),
which was conducted in the early 1990s. This example is based on the
feasibility study of Sutong Bridge started in the late 1990s. All analyses in
this example were conducted by Visual Bridge Design System (Wang and
Fu 2003, 2005).