The Impossible Bridge | National Geographic

again a low bridge is ruled out because
of heavy boat traffic but there’s no
airport on the Swedish shore they can
build as big as they want and they need
it big very big to clear boat traffic
the bridge will have to be at least 200
feet above the water the center span at
least 1500 feet long to meet these
challenges with the best possible bridge
the consortium holds a design
competition one of the most spectacular
proposals requires building the largest
arch bridge in the world I think you
don’t really get an idea of the
magnitude of this arch you might get it
from the ship going underneath but it
really is big it would be a monument of
some kind but arch bridges have an
Achilles heel is the arch sweeps down
toward the water the clearance for large
ships decreases eventually to nothing
you always run the risk that a ship
could get in there therefore you have
the risk of hitting the bottom part of
the arch and then the whole thing
collapses if not an arch what about a
suspension bridge suspension bridge
technology enables the longest spans of
any design to enormous cables stretch
their length
shorter cables dangled down to hold the
roadway but connecting cables to more
cables make suspension bridges very
flexible trains don’t do well when
tracks bend under their roads and
railway traffic is so heavy that if you
have a suspension bridge you will find
if you look at it from the side that if
the Train will always go up a little
pole she were always going uphill all
the time suspension is ruled out arch
ruled out so engineers turn to the one
design that can answer all their
concerns a cable-stayed bridge its
structure is rigid enough for heavy
train traffic because the support cables
attached directly to the towers
and there is a bonus cable-stayed
bridges are cheaper to build than
suspension bridges not having the two
enormous main cables saves tons of steel
it’s a winner the best design to meet
all the orisons needs is a towering
two-level cable-stayed bridge