Extradosed Bridge Technology
From 1994 to 2008, over fifty extra dosed bridges have been constructed worldwide, and the preferred Proportions and cable arrangements have evolved. While there are many articles available on the design of specific extra dosed bridges, very little has been published on their design from a general perspective.
The idea of using stay cables to support a bridge has been around for a while, it was first applied during 1800's in the UK (incorporated with suspension bridges), many of which had failed due to insufficient resistance to wind pressure, unaccountability of secondary effects of the forces (lack of understanding of the mechanics of such a bridge was also a reason). But in the 1900's, several factors contributed to successful implementations: Better methods of structural analysis of statically indeterminate structures (via computers) Development of orthotropic steel decks High strength steels, new methods of fabrication and erection.
A box girder supports the deck so as to reduce buckling of the deck from high compressions, twisting or torsion, and distribute among the stays non-uniform loads. Cables are made of high-strength steel, usually encased in a plastic or steel covering that is filled with grout, a fine grained form of concrete, for protection against corrosion.
The function of the extra dosed cables is also to prestress the deck.
H ~ L/15 to L/8
h ~ L/50 to L/30
Maximum cable stresses 0.60 fpu(UTS).
The idea of using stay cables to support a bridge has been around for a while, it was first applied during 1800's in the UK (incorporated with suspension bridges), many of which had failed due to insufficient resistance to wind pressure, unaccountability of secondary effects of the forces (lack of understanding of the mechanics of such a bridge was also a reason). But in the 1900's, several factors contributed to successful implementations: Better methods of structural analysis of statically indeterminate structures (via computers) Development of orthotropic steel decks High strength steels, new methods of fabrication and erection.
A box girder supports the deck so as to reduce buckling of the deck from high compressions, twisting or torsion, and distribute among the stays non-uniform loads. Cables are made of high-strength steel, usually encased in a plastic or steel covering that is filled with grout, a fine grained form of concrete, for protection against corrosion.
Extra dosed bridge action
Decrease in cable inclination leads to increase in axial load in the deck and decrease in vertical component at cable anchorage points.The function of the extra dosed cables is also to prestress the deck.
H ~ L/15 to L/8
h ~ L/50 to L/30
Maximum cable stresses 0.60 fpu(UTS).
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NBM&CW October 2010
