Cable-stayed bridges - Computational Analysis and Design of Bridge Structures - page 355

the construction errors in certain key parameters, such as girder segment
weights, concrete creep, and shrinkage properties. Other prediction models
based on grey prediction theory are also practiced to identify errors (Chen
et al. 2011). The back propagation neural network method is also used in
the construction control of cable-stayed bridges (Li et al. 2007).
Incremental jacking of erection cables and cable jacking stress adjust-
ment are common during erection and for the purpose of construction con-
trol, for example, jacking the erection cables to a certain level initially when
the traveler carriage is positioned and jacking the erection cables again
when the girder segment is positioned. When needed, forces of a group of
cables can be adjusted by rejacking to meet certain control goals. A special-
purpose analysis tool is preferred to guide the adjustment of multiple cables.
The expected cable stresses to meet these goals are usually not the same as
the jacking stresses because the jacking process is usually conducted one by
one. When one pair of the cable is rejacked, stresses of all the other cables
will be redistributed. The jacking sequences should be carefully scheduled,
and the analysis should truly reflect the sequences.
11.4 PrinCiPle and Modeling
of CaBle-stayed Bridges
There are many considerations in modeling cable-stayed bridges. The first is
to identify an analysis tool. Different FEA packages have different features
regarding the special requirements for analyzing a cable-stayed bridge. The
following lists a few items that need to be identified for any particular FEA
package:
1. How a desired state is determined?
2. How backward and forward analyses are processed?
3. How jacking a cable is simulated?
4. How sag effects, initial stresses, and large displacement are considered?
5. How the live load envelops are obtained?
The second question is whether to build the model in 2D or 3D. This was an
important question several years ago when 3D analyses, including 3D pre-
processing and postprocessing, were more expensive than it is now. Because
the lateral dimension is much less than the longitudinal and vertical dimen-
sions, it is adequate to use 2D modeling to conduct analyses for prelimi-
nary design purposes. Nowadays considering that advanced 3D processing
tools are widely available and the computing capacity and performance
are significantly advanced, the 3D modeling should be used whenever fea-
sible. By using 3D modeling, not only can the analysis be more realistic
and accurate, but the stiffness and weight of pylons and their connection