Arch bridges - Computational Analysis and Design of Bridge Structures - page 274

piles to resist the horizontal force and limit the displacement due to this force.
These stirring piles are connected to each other to improve the integrity of
the system. The large number of foundations and addition of stirring piles are
partly due to the great working and construction loads.
Due to the horizontal force generated by live loads, the abutment and
foundations are also strengthened in the horizontal direction by the use of
prestressing concrete. In addition to vertical piles, inclined piles are also
used to the abutments.
9.2.1.2 Arch ribs
The arches are segmentally constructed using a cable-stayed cantilever
method shown in Figure 9.9a. Each section of the arch was stayed back to
the temporary towers at either side of the arch after being welded to the
previous section. This significantly reduces the bending stresses in the arch
during construction and instead puts the constructed arch section into com-
pression, as it would be upon completion. Cables from the temporary tow-
ers to the ground are connected at the location of the foundations that will
be resisting uplift on completion of the bridge. Using the same foundations
reduces the cost as extra supports were not needed during construction.
As shown in Figure 9.9b, each erecting segment contains two segments of
the main arch ribs laterally, where these two segments are connected by a
horizontal wind brace box section. A mobile carriage is used to lift braced
arch sections up from barges. A computer-controlled system was used to
synchronize the strand jacks during deck lifting. The carriage then holds the
section in place while it is welded to the previous section. This secure system
is favored as it reduces differential movement between the existing and new
segments, allowing smoother application of the welding process.
9.2.1.3 Deck girders
For the midspan girders, a conventional suspension bridge construction
method is used. After the closure of the main arch, high-strength tie cables
are installed to connect the two ends of the deck at side spans. The horizon-
tal forces from the deck ends are transferred to the main arch at springing
through the side-span arches, as shown in Figure 9.9.
After the tie cables are installed and tensioned, the construction towers
and stayed cables are removed. The segmental erection of the deck girder
starts. The transporting and lifting of deck girder segments are similar to
those of arch segments. The girders are installed from the center of the arch
outward, to ensure that the sag in the horizontal cables is uniform and no
distortion of the deck occurred. Another reason is that the load being put
on the arch can be carried in compression whereas if spans are introduced
at other points, large bending moments will be induced in the arch.