Civil Engineering Reference
In-Depth Information
Inside surface
coated with grease
Hole with
fittings to
put grease
Bronze bushing
FIGURE 7.50
Sketch for roller support on the bridge.
with thermal expansion due to the grease of the internal surface and the presence
of bronze to reduce the friction. Therefore, in the mature structure, corrosion will
increase the coefficient of friction, which may cause higher stresses on the bridge
by preventing movement (the coefficient of friction may be greater than 10% due
to corrosion and depletion of the bronze bushing).
The procedure for refurbishing the roller bearings is critical because it is
based on removal of the old, corroded rollers and cleaning up the existing steel-
work and bronze bushings.
1. The first step is to install a temporary lateral bracing to support flare-
bridge lower chord during refurbishment of rollers. Then install hydraulic
jacks to lift and support the flare bridge as required and lift the flare bridge
by jack-up for 40 mm to unload rollers. This distance is the maximum
allowable, obtained from structural analysis, that will not place overstress
on the bridge.
2. The repair procedure starts with removal of all corrosion on the outer parts
using tools like a needle-gun or grit-blast to reduce the diameters of the protrud-
ing parts so that they can pass through the bushings without causing damage.
Cut the roller and then remove it by hammering the remaining roller portions
through the bronze bushings from outside and removing them.
3. After cleaning up and removing corrosion and rust scale from surfaces,
apply paint to the bearing support steelwork and also inspect, clean and
grease the bronze bushings. The bearings are believed to be intact. If
there is wear or corrosion, then they should be cleaned up as far as possible
and the surfaces of the bushings polished without increasing the hole dia-
meter by more than 2 mm. Finally, install the new rollers, grease the rollers
and apply paint to roller ends.
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