Bridge geometry - Computational Analysis and Design of Bridge Structures - page 571

control point that is perpendicular to line p n n − 1 , the axis of Lat′ as a line
can be known. Further, the direction of positive Lat′ can be determined by
referring the control point.
Having Long′ and Lat′ defined, Alt′ can be simply derived from a cross-
product operation of Lat′ × Long′. Thus, the direction cosine matrix, as
defined by Equation 18.12 for the transformation between the current
casting system and the global system, is established. Once the λ matrix is
obtained for the current casting segment, transforming of control points
between the global coordinate system and the casting system can be per-
formed further.
When implementing geometry control program for precast segmental
bridges, geometry transformation can be simply called as underlying func-
tionalities. Other procedures such as calculating setup values, collecting
as-cast values, and detecting errors can follow the discussions in the earlier
sections. Together with regular tabular data reports, a 3D rendering, as
shown in Figure 18.20, truly reflecting segment geometries, setup values,
and as-cast measurements, will be greatly helpful for both designers and
field engineers.

18.6.8 an example of short - line match
casting geometry control
To demonstrate the geometry control of precast segmental bridges in cast-
ing yard, an example of a single-span curve bridge of radius 183 m (600′)
is presented. As the plane curve shown in Figure 18.23, the example span
contains 16 segments with a total length of 37.6 m (123.5′). Figure 18.23
contains two centerlines: (1) The theoretical curve and (2) as-cast curve, or
the obtained curve (these two curves, however, are overlapped on each other
due to minor discrepancies). However, they may not show clearly because
the obtained curve is very close to the theoretical curve. Figure 18.24 shows
a prediction of setups for segment No. 10 so that casting of segment No. 11
would be in the correct position. This prediction is based on the survey of
all previous segments. Values shown in Figure 18.24 indicate that the dry
segment should be positioned by jacking its support so that the segment to
be casted will be at the right position after assembled. Figure 18.25 shows
the survey points and values after segment No. 13 is casted, which will
affect the prediction of the setup of this segment after it is moved to match
position.

Figure 18.23 The plane curve of a segmental bridge with 16 precast segments.