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Galloping Gertie
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Comparison of the Bridges
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Today the center span and other debris
lie on the floor of Puget Sound, where they fell. A site plan of these
remains was developed from sonar soundings of the Narrows. The remains
of the center span and anchor blocks are readily identifiable. The side
scan information was then used to develop the documentary "Gertie
Gallops Again," prepared by Tacoma Municipal Television for the show
"CityScape". In 2000, this workup of the ruins was used to develop a
site plan for the new Tacoma Narrows Bridge.
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main channel piers were undamaged during the failure of the original
bridge and were used to support the second bridge with only minor
modifications to the concrete pedestals under the new steel tower legs.
The original construction of Pier 5 was one of the most difficult ever
attempted, establishing a world record for depth of water in which a
caisson had ever been landed. Water depth, along with tidal currents of
nine miles per hour at the site, required extreme caution and ingenuity
on the part of the engineers and contractors. Thirty concrete anchors,
each weighing approximately 600 tons and connected to the caisson with
90 one-inch diameter wire cables, were required to hold the caisson
against the current. At times the level of water at one end of the
caisson would be seven to eight feet higher than at the other. Holding
construction barges alongside the caisson was extremely difficult.
Steel cutting edges were attached to the bottom of the caisson. After
the caisson was lowered to the bottom of the channel in 135 feet of
water, the cutting edges assisted in penetrating through 90 feet of
sand, gravel, and boulders where the bottom of the caisson was finally
positioned at a depth of 225 feet below mean low tide. Lightweight
concrete was used in the roadway deck of the present bridge to lessen
the load on the piers. However, the total superstructure weight of the
present bridge exceeded the first bridge by approximately 1.6 times per
lineal foot. The designers determined that this additional weight would
not cause excessive overloading of the foundations. The original anchor
blocks were also used in the second bridge, but were modified
substantially due to the greater weight of the superstructure. This
weight increased the horizontal force in the main cables from the
original 28 million pounds to 36 million pounds. In addition, the new
cables were spaced 60 feet apart compared to the original 39 feet. The
concrete anchorage was modified by removing the sides and blasting to
the top of the footing blocks. Then, new anchor bars were installed for
the main cables. In addition eight feet of concrete was added on each
side, and extending the back of the anchor 20 feet to its full height.
The additional width and length, in effect, provided a yolk or "U"
configuration around the old concrete core that remained. |
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Every reasonable precaution was taken
to stabilize the structure and insure against any possibility of
noticeable motion. One of those precautions, and a feature unique to
this bridge, is the design of the roadway deck. Open steel grid slots
were installed between each of the four traffic lanes and at both
curbs. These open steel gratings function as vents to relieve
oscillations created by passing wind. The gratings are bonded to the
concrete to preserve slab continuity across the full roadway. In tests
the use of these slots was an effective method of reducing the forces
which cause oscillation and, consequently, constitute a large factor in
stabilizing the structure.
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| Categories |
Galloping Gertie ( 1940 ) |
Tacoma Narrows Bridge ( 1950 ) |
| Total Structure Length |
5,939 feet |
5,979 feet |
| Suspension Bridge Section |
5,000 feet |
5,000 feet |
| Center Span |
2,800 feet |
2,800 feet |
| Shore Suspension Spans (2), each |
1,100 feet |
1,100 feet |
| East Approach and Anchorage |
345 feet |
365 feet |
| West Approach and Anchorage |
594 feet |
614 feet |
| Center Span Height Above Water |
195 feet |
187.5 feet |
| Width of Roadway |
26 feet |
49 feet 10 inches |
| Width of Sidewalks(2), each |
5 feet |
3 feet 10 inches |
| Diameter of Main Suspension Cable |
17.5 inches |
20.25 inches |
| Weight of Main Suspension Cable |
3,817 tons |
5,441 tons |
| Weight Sustained by Cables |
11,250 tons |
18,160 tons |
| Numver of No. 6 Wires Each Cable |
6,308 |
8,705 |
| Weight of Shore Anchors |
52,500 tons |
66,000 tons |
| Total Length of Wire |
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20,000 miles |
| Towers: |
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| Height Above Piers |
425 feet |
467 feet |
| Weight of Each Tower |
1,927 tons |
2,675 tons |
| Piers: |
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| Area |
118 feet, 11 inches by 65 feet, 11 inches |
118 feet, 11 inches by 65 feet, 11 inches |
| East Pier, Total Height |
247 feet |
265 feet |
| East Pier, Depth of Water |
140 feet |
140 feet |
| East Pier, Penetration at Bottom |
90 feet |
90 feet |
| West Pier, Total Height |
198 feet |
215 feet |
| West Pier, Depth of Water |
120 feet |
120 feet |
| West Pier, Penetration at Bottom |
55 feet |
55 feet |
These days most are aware of the
location, identification and recoveries from the Titanic. The Titanic
was a large ship but in comparison it would take 5.56 Titanic’s end for
end to occupy the space that Galloping Gertie now occupies. In raw
materials the bridge contained 5.0 times that of Titanic. These figures
make Galloping Gertie the largest man made structure ever lost at sea.
In addition the current swept bottom of the Narrows has now become the
largest single man made reef supporting an abundance of marine life.
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