Civil Engineering Reference
In-Depth Information
from wire reelers located close to one anchor. Initially, the spinning wheel is
docked at the end where the wire reelers are located. The live end of the wire
unreeled from the reeler is passed through the spinning wheel in a way of
top-in and bottom-out. The live end is then tied to anchor shoes. When the
spinning wheel moves away from the wire reeler side (the approach route),
it brings two wires to the other side. The wire laid from the bottom of the
wheel is called dead wire, which will be placed into the cable former while
the wheel is moving. The wire laid from the top of the wheel is called live
wire, which will be stored on top of the cable former while the wheel is mov-
ing toward the other end. The feeding speed of the wire reeler is double com-
pared to the wheel moving speed. When the wheel reaches the other anchor,
the looped end of the two wires will be prepared to connect to an anchor
shoe. Then, the wheel will return back to the wire reeler side (the return
route). The top wire (the live end) will be laid into the cable former while the
wheel moves back. The wire reeler will stop feeding while the wheel returns.
Once it reaches the anchor at the wire reeler side, the wire will be taken off
the wheel to form a looped end so as to connect to an anchor shoe and then
is taken on the wheel again to start another round.
After each wire is laid out, it has to be adjusted. When all wires of a strand
are erected, they will be banded into the strand shape. Apparently, the AS
method is simple and needs less equipment on site. However, erecting cable
wire by wire is time consuming and the process relies on weather conditions.
Instead of erecting wire by wire, in the PPWS method, all wires of a
strand are shop-fabricated and socketed into the final shape and packaged
on reels. When erecting, a complete strand will be pulling from one end
to another by hauling cables. As the strand is prefabricated earlier, when
it is ready to anchor, anchor shoes will be adjusted according to the dif-
ference in temperature so as to make the tension of each strand as even as
possible. Compared with the AS method, PPWS method will save time on
site significantly. Individual wire adjustment is eliminated too. As the strand
is formed in shop, quality can be well controlled and cost will be lowered.
After all strands are erected, the cable will be squeezed by squeezing
machine and lashed at a certain pitch to form a round shape. Cable clamps
or bands will be installed at each design locations for suspender connec-
tions. As the cable will be deformed much while the stiffened girder is
erected, offsets to the suspender locations should be already considered in
the design locations. The final step for cable erection is to lash the cable
with wrapping wires and to protect the cable with coating treatment.
12.2.3 erection of stiffened girder
The erection of stiffened girders, as shown in Figure 12.5, can start from
either center of the main span or end of the side span or pylons. Considering
the change of the suspender angle to the cable clamps, the sequence of
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