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Continued...
The pintle bearing on which the bridge rotates consists of a
convex steel plate on the central pier which marries with a concave block of
Orkot resin composite material on the bridge deck, which provides some
shock-absorption when the bridge is being moved. A combination of steel and
Orkot is also used for the seven bearing blocks on which the bridge rests when
it is in the ‘road open' position. These are curved in the lateral direction to
allow for movement in the bridge caused by traffic, wind, temperature and other
factors.
The use of Orkot and steel avoids catastrophic failure, which can
occur with conventional rolling element bearings. Instead, the components will
gradually wear. ‘We believe this is the first time this combination of materials
has been used for bridge bearings', said James Hill, the project engineer with
Bennett Associates.
All the bearings have been designed to be replaceable without
special tooling and without closing the bridge to road traffic. Provision has
been made so that conventional jacks can be used to take the weight off each of
the static bearings, remove them and replace them, working entirely below the
deck. The pintle bearing can also be replaced when the bridge is open to
traffic, as it is not loaded in this position. It is also possible to replace
the wearing surfaces of bearings during a slightly extended swinging operation.
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