| Reinforced Concrete Sentinels
The Gig Harbor and Tacoma towers on the new Tacoma Narrows Bridge rose
rapidly once crews capped off the caissons (bridge foundations) in the
summer of 2004.
In August 2004, tower construction began in earnest with both towers
exceeding the 500-foot mark in early June 2005. A mere 10 months after
they were started, concrete pours on the sentinel-like structures were
finished. The final 510-foot elevation includes the six-foot "saddle"
(a steel casting that cradles the cable) atop the tower legs.
One key difference between the new and existing bridge is that the new
towers are constructed from reinforced concrete instead of steel. The
new tower legs are hollow box structures that taper in in length from
the top to the bottom while remaining constant in width.
Over the course of the project, and in order to accommodate the ever-growing
towers, the tower crane was raised three times - to an ultimate height
of 600-plus feet above water.
During tower construction, WSDOT staff often found themselves answering
this comming question from members of the public: “Did you know
the towers are leaning?” Yes we know, and happily they were designed
to lean. The towers lean toward each other so the stiffening truss (the
bridge deck and its associated components) can
pass through the tower opening while allowing the suspender cables (cables
that will support the deck) to be perfectly vertical.
See glossary for more bridge engineering terms.
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A tower is the vertical structure
in a suspension bridge (or cable-stayed bridge) that holds up the
suspension cables. |
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The new towers are constructed from reinforced concrete
instead of steel, which is used on the existing bridge. |
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Final elevation of the towers
is 510 feet above sea level, which includes the six-foot cable saddle
atop the tower legs. By comparison, the Seattle Space Needle is 138
feet taller, measuring 605 feet high. |
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The tower legs are hollow box
structures that taper in width from the top to the bottom. |
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