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Currently AASHTO allows the use of a combination of
50% external and 50% internal tendons in precast segmental concrete
bridges in seismic areas. Recent research at the University of
California San Diego has shown that this practice may not provide
the adequate ductility necessary in seismic regions. The research
studied the following combinations of post-tensioning: 50% internal
50% external, 100% external (unbonded tendons), and 100% internal
(bonded tendons).
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Long-term penetration of chlorides from de-icing
agents or aggressive natural environments can accelerate corrosion
and cause serious damage to deck reinforcement. Thus, the
minimization of cracking within any protective overlay layer is
important to the long-term durability of the deck. One method to
prevent overlay cracking is the application of precompression,
especially in conjunction with the post-tensioning of the rest of
the structure.
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Figg Engineering Group has designed and
successfully tested a new cradle stay system that will be used
initially on the Maumee River Bridge in Toledo, Ohio. The new
system will revolutionize cable-stayed bridge designs worldwide by
allowing a wider range of pylon shapes and saving bridge owners
significant money.
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