Cable-stayed bridges - Computational Analysis and Design of Bridge Structures - page 354

In the control of Sutong Bridge (a steel box girder with the main span
of 1088 m in Jiangsu, China), which was once the world record holder
for main span length, sensitive analyses revealed that deviations of creep
and shrinkage of pylons, girder segment weight, length of the girder seg-
ments and length and Young's modulus of cable stays were the primary
control parameters that would significantly influence the girder elevation.
The deviations of the height of the steel anchor boxes, cable weights, and
girder stiffness were the secondary control parameters that had moderate
influences. Effects of other factors such as Young's modulus of pylons, the
height of anchors at the deck end, the verticality of steel anchor boxes, and
the shrinkage of welding between girder sections were considered negli-
gible. Wind and temperature effects are also sensitive to girder elevation.
It is clear that all errors can be minimized only by improving measure-
ment systems and quality control processes, and it is impossible to eliminate
these errors completely. However, knowing the errors and incorporating
them into engineering assumptions so as to better predict a countermea-
sure, that is, cable jacking stresses in the next erection to control the girder
geometry or the primary target to meet design requirements, is achievable.
That is the whole purpose of the construction control.
11.3.4 general procedures of construction control
The procedures of construction control and sensitive analysis are two impor-
tant issues in the construction of a cable-stayed bridge. The steps, which
include considering property errors and modifying FEA models, may be
complicated and tedious. In general, these steps can be simplified as follows:
1. Use the theoretical model in initial stage and jack the first pair of
cables at theoretical stress level.
2. Compare the observations with forward analysis results and analyze
the errors.
3. Adjust the model when the errors in step (2) exceed a preset tolerance.
4. Forward-analyze the next erection based on the modified model to
obtain the jacking stress of the next erection cables.
During these procedures, sensitive analyses may be required to rank these
numerous construction errors. Once the differences between observa-
tions and expectations are known and a few variables that are ranked as
the most sensitive are identified, certain error analysis methods or algo-
rithms can be used to determine the variations, which will be the basis of
the model adjustment. Lin (1983) first applied the Kalman filter method
to the construction control of Maogang Bridge, a PC cable-stayed bridge
located in Shanghai that is marked as a milestone of cable-stayed bridge
construction in China. Nowadays, this method is widely used to analyze