In a curved
prestressed bridge, how should the guided bearings in piers of
the curved region be oriented with respect to the fixed bearing in
abutment?
Vincent
T. H. Chu
is renowned internationally as
walking
encyclopedia of civil engineering.
Author of a number of
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including Young Engineer of
the Year Award 2008
(Merit) by the Hong
Kong
Institution of Engineers &Ombudsman’s
Award 2007 (under
complaint-related category). He is also listed
in
11th Edition of Marquis Who's
Who in Science and Engineering. ConcreteBasics.org
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around the world.
To determine
the orientation of guided bearings, one should understand the movement
of
curved region of a prestressed bridge. Movement
of prestress and creep are
tangential to the curvature of the bridge (or along longitudinal axis)
while
the movement due to temperature and shrinkage effects are in a
direction
towards the fixed pier.
The diagram
below shows how the guided bearings in piers of the curved region is
oriented with
respect to the fixed bearing in abutment:
If the direction
of guided bearings is aligned towards the fixed bearing in the
abutment, the
difference in direction of pretressandcreepmovementandtheguideddirectiontowardsfixedbearingwould
generate a locked-in force in
the bridge system.
The magnitude of the lock-in force is
dependent on the stiffness of deck and supports. If the force is small,
it can
be designed as additional force acting on the support and deck.
However, if the
force is large, temporary freedom of movement at the guided bearings
has to be
provided during construction.
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