Tacoma Narrows Bridge (1950) facts for kids
Quick facts for kids 1950 Tacoma Narrows Bridge |
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The 1950 Tacoma Narrows Bridge in 1988
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| Coordinates | 47°16′00″N 122°33′00″W / 47.26667°N 122.55000°W |
| Carries |  SR 16 (4 lanes Westbound) |
| Other name(s) | Sturdy Gertie, Westbound Tacoma Narrows Bridge |
| Maintained by | Washington State Department of Transportation |
| Characteristics | |
| Design | Suspension |
| Total length | 5,979 feet (1,822.4 m) |
| Longest span | 2,800 feet (853.4 m) (side spans 1,100 feet (335.3 m)) |
| Clearance above | 186.4 feet (56.8 m) |
| Clearance below | 195 feet (59.4 m) |
| History | |
| Opened | October 14, 1950 |
The 1950 Tacoma Narrows Bridge is a suspension bridge in the U.S. state of Washington. It carries the westbound lanes of Washington State Route 16 across the Tacoma Narrows strait. This bridge connects the city of Tacoma with the Kitsap Peninsula.
Opened on October 14, 1950, this bridge was built in the same spot where the original Tacoma Narrows Bridge once stood. That first bridge collapsed in a windstorm on November 7, 1940. The 1950 bridge is the older of the two twin bridges that now cross the Tacoma Narrows. For many years, it carried traffic in both directions until 2007. When it was built, it was the third-longest suspension bridge in the world. Only the Golden Gate Bridge and George Washington Bridge were longer. Today, it is the 46th longest.
Engineers started designing a new bridge soon after the first one fell. However, building it was delayed for a few reasons. There were some engineering problems, and World War II meant that a lot of steel was needed for the war effort. Also, the state of Washington had trouble finding insurance for the bridge. Because of these issues, construction didn't begin until April 1948.
The new bridge was designed to be much stronger and safer. It had a wider deck and taller, wider towers than the first bridge. These changes helped fix the wind problems that caused the original bridge to collapse. The bridge opened to the public on October 14, 1950. It carried traffic for over 40 years. People had to pay tolls to cross the bridge until 1965, which was 13 years earlier than planned!
By 1990, more and more people were moving to the Kitsap Peninsula. This caused a lot of traffic on the bridge, more than it was designed to handle. In 1998, people in Washington voted to build a second bridge next to it. After some protests and court cases, construction on the second bridge began in 2002. The second bridge opened in July 2007 for eastbound traffic. The 1950 bridge was then changed to carry only westbound traffic.
Contents
How Was the Bridge Designed?
The plans for the 1950 Tacoma Narrows Bridge were started not long after the 1940 collapse of the first bridge. In July 1941, the Washington Toll Bridge Authority chose Charles E. Andrew to lead the design of the new bridge. He had also helped with the design of the first bridge. Other experts like Dr. Theodore von Kármán and Glenn Woodruff also joined the design team. Dexter R. Smith was the main designer.
By October 1941, less than a year after the first bridge fell, a basic design for the new bridge was ready. This new design looked a lot like the first plans for the 1940 bridge. At that time, building the new bridge was expected to cost about $7 million.
The U.S. Navy wanted a bridge that could carry both cars and trains. They suggested a different type of bridge called a steel-cantilever bridge instead of a suspension bridge. However, this would have cost an extra $8.5 million, so the idea was not used.
Engineers needed to test the new design very carefully. They didn't fully understand what caused the first bridge to fall. So, they decided to design the new bridge and then test small models of it. They built a special wind tunnel at the University of Washington for these tests. Charles Andrew said, "The only way to attack the problem, was to design a bridge, then build a model of that design and subject it to wind action." Professor F. B. Farquharson, who had studied the first bridge, did the testing.
Professor Farquharson worked on the new bridge design from late 1941 through 1945. He confirmed that the first bridge collapsed because it was too flexible and the wind created strong forces. The new designs used a deep, open stiffening truss instead of a solid plate girder. This made the bridge much stronger.
Testing involved 200 different designs. They tested how the bridge would react to wind from different angles. They also tested designs with open strips of wind grating in the roadway. This added more stability. They even tested motion damping devices, which are like shock absorbers, to reduce movement. All these steps helped make the bridge as stable as possible.
After spending $80,000 on design and testing, the final design was ready on December 5, 1945. The new bridge was expected to cost $8.5 million to build.
What Made the New Design Special?
The final design of the 1950 Tacoma Narrows Bridge was very different from the first bridge. Instead of a thin plate girder, the new bridge had an open-air stiffening truss that was 33 feet (10 m) deep. This truss formed the road deck. The new towers were taller and wider than the old ones. They supported the bridge's main cables, which were 20+1⁄4 inches (510 mm) thick. The new anchor blocks were also much larger and stronger.
Some parts of the old bridge were used in the new design. The tower bases were made bigger and raised 17 feet (5.2 m). On the west side, a 450-foot (140 m) long approach viaduct from the old bridge was kept. This viaduct was strengthened and used as part of the 1950 bridge.
The road deck itself was very innovative. It was 46-foot (14 m) wide and had four lanes of traffic. Each lane was 9+5⁄8 feet (2.9 m) wide. What was special was that each lane was separated by a 3-inch (76 mm) deep, 33-inch (840 mm)-wide open-air wind grate. These grates helped air flow through the bridge, making it more stable. There were also sidewalks on both sides, protected by a 4-foot (1.2 m)-high railing.
How Was the Bridge Built?
Building the new Tacoma Narrows Bridge was delayed for almost ten years. This was mainly because of World War II, which needed a lot of steel. Also, the state had trouble getting insurance for the new bridge. Finally, on April 30, 1947, the governor announced that insurance was arranged.
In August 1947, Washington asked companies to bid on the construction. By then, the cost had gone up from $8.5 million to $11.2 million. Bethlehem Pacific Steel Corporation won the bid for the main structure. John A. Roebling's Sons Company won the bid for the suspension cables.
After more delays with money, the state finally got a $14 million bond. This money would be paid back using tolls from the bridge. On March 12, 1948, the state finished getting the money. With steel becoming available, construction began quickly. On April 9, workers started clearing the ground at the old bridge's east cable anchorage.
Building the Anchorages
The new bridge was going to be much heavier than the old one. So, the old cable anchorages had to be changed and partly taken down. The center parts of the old anchorages were kept. New steel eyebars, which are like giant metal rods, were put in place. These would hold the much heavier cables. Each new anchorage weighed 54,000 short tons (49,000 t) and was built deep into the ground. Building these started in the summer of 1948 and continued into 1949.
Building the Tower Bases
The water in the Narrows is very deep, about 150-foot (46 m). Because of this, the tower bases, called pedestals, are huge. Each one is as big as a 20-story building! They are designed to stand strong against the daily 7-knot (13 km/h; 8.1 mph) currents and the 15-foot (4.6 m) tidal changes. Each pedestal used 34,000 cubic yards (26,000 m3) of concrete.
The old bridge's tower pedestals were still strong after the first bridge fell, so they were reused. However, the old towers had rusted at their bases from salt water. So, engineers built new tops for the pedestals. These new tops were raised 17 feet (5.2 m) to prevent rusting and were made wider for more strength. The east and west pedestals were finished by mid-December 1948.
Building the Towers
The towers of the first bridge had four box-shaped supports. The new towers were designed differently. They were the same width from top to bottom and had a strong X-bracing system. This system used three deep X-brace supports below the road deck and three double-X brace supports above it.
Tower construction began on January 1, 1949, and went very fast. By April 1949, the 21-short-ton (19 t) steel cable saddles were ready to be lifted. These saddles hold the main cables. On April 13, 1949, an earthquake measuring 7.1 hit the area. The earthquake caused the towers to sway 6 feet (1.8 m). This made one of the cable saddles break its bolts and fall 510 feet (160 m) down. It missed the pedestal and went through a barge, sinking it! The saddle ended up 135 feet (41 m) below the water. Divers found it, and it was brought up, repaired, and put back in place. The earthquake delayed the completion of the towers. Work continued, and by July 17, both towers were finished.
Spinning the Cables
Building the main cables started in July by putting up 10-foot (3.0 m) wide walkways. On July 17, 1949, the first walkway line was pulled across the Narrows by a tugboat. These walkways were made of wire, fencing, and wood slats. They were built in 200-foot (61 m) sections. By September 15, the walkways were done, and the equipment for spinning the cables was ready.
To make the main cables, a special plant was set up. About 100,000,000 feet (30,000,000 m) of steel wire, enough for both main cables, arrived in large coils. This wire was then wound onto huge reels. Each reel weighed 9 short tons (8.2 t) and held 36 miles (58 km) of wire.
Cable spinning began on October 13. Each main suspension cable was made of 19 strands, and each strand had 458 steel wires. This meant a total of 8,705 wires per cable! Workers worked three shifts, 24 hours a day. Despite some delays from bad weather, the main cables were finished on January 16, 1950. The cable bands and vertical suspender cables were installed by March 7, and then deck construction began.
Building the Stiffening Truss
Building the new road deck and stiffening truss was done differently than for the first bridge. For the 1950 bridge, large sections of the stiffening truss were made beforehand. These 32 feet (9.8 m)-by-60 feet (18 m) sections were lifted into place. After these sections were in place, special cranes were used to assemble the rest of the deck.
The stiffening truss had outer parts called "chords" that formed the top and bottom. These were installed first. Then, the diagonal and vertical truss members were put on the sides. Next, 11-foot (3.4 m) deep "floor beams" were installed every 32 feet (9.8 m). These beams helped stiffen the deck. After that, diagonal bracing and lateral bracing struts were added. Finally, eight 18-inch (460 mm) deep I-beam "stringers" were installed. This completed the steelwork for the deck.
Unlike the first bridge, where deck sections were lifted from the middle outwards, the new bridge's stiffening truss was built starting at each tower and moving outwards. Four work crews worked together, completing about 128 feet (39 m) of steelwork each day. By May 1949, the work was almost done. On June 1, the steel stiffening truss of the road deck was finished.
Finishing the Deck
Throughout the summer of 1950, about 200 people worked on the final parts of the 1950 Tacoma Narrows Bridge. Workers wrapped and sealed the suspender cable bands. The railings on the sidewalks were also completed. By August 22, the road deck was taking shape as concrete was poured for the roadway. Painting began that week. The bridge was painted its first coat of "Narrows Green," a grayish-green color. By September 30, the toll plazas were finished. The hydraulic damping mechanisms were installed, and workers began removing the temporary platforms.
Work also happened on the west end of the bridge. Workers changed the 450-foot (140 m) long approach viaduct that was part of the 1940 bridge. They added bracing to make it wider, from 39 feet (12 m) to 48 feet (15 m), to match the new road.
Opening Day
The bridge opened for traffic on October 14, 1950. People had to pay tolls to cross. On opening day, it cost fifty cents for a car and driver, and ten cents for each extra passenger. Thousands of people came to the opening ceremonies, including Governor Arthur B. Langlie. After 30 months of building, the Narrows was bridged again!
Traffic on the bridge grew steadily in the first few years. Five years after it opened, about 4,699 vehicles crossed each day. By 1960, it was 6,218 vehicles per day. In 1965, fifteen years after the bridge opened, the number doubled to 11,267 vehicles per day. Because of this high traffic, the Washington Toll Bridge Authority decided to remove the tolls. On May 14, 1965, Governor Dan Evans signed the law that removed the tolls. This was a big moment because the bridge had been paid off 13 years ahead of schedule!
Traffic Growth and a New Bridge
For the first few decades after it opened, traffic was not a problem. Highway 16, which connected to the bridge, was expanded over time. By the late 1980s, more homes and shopping centers were built in Gig Harbor. This caused traffic to grow a lot. By 1990, an average of 66,573 vehicles crossed the bridge each day. This was more than it was designed for. Traffic jams became common, especially on the east end, stretching for miles. By 2000, about 88,000 vehicles crossed the bridge daily.
This led the state to ask people to vote on building a new bridge. After some debates and court cases, construction for the new bridge officially began on October 5, 2002.
Bridge Design Legacy
The collapse of the 1940 Tacoma Narrows Bridge and the design of the 1950 bridge led to important new ideas in bridge building. The 1950 bridge was the first to be designed and tested in wind tunnels. It was also the first suspension bridge built with hydraulic motion damping devices, which help control how much the bridge moves.
Maintenance and Today's Bridge
The 1950 Tacoma Narrows Bridge has a very careful maintenance plan that lasts all year. Crews often replace steel parts and check the cables and towers. This work is usually done at night or when there isn't much traffic. Painting the bridge is a huge job. It takes ten years to paint the entire bridge, and workers only paint during the summer months. The bridge's color is called "Narrows Green," which is a grayish-green hue. This was also the color of the first bridge.
The bridge has also survived several major earthquakes. One happened during construction on April 13, 1949, which caused a 21-short-ton (19 t) steel cable saddle to fall from the east tower. Other strong earthquakes hit in 1965, 1999, and the 2001 Nisqually earthquake. The bridge was not damaged in these earthquakes. However, the cable saddle that fell in the 1949 earthquake still rusts faster than the others because it was in salt water for three days.
On the bridge's 50th anniversary in 2000, an inspection firm said it was "one of the best for its maintenance and condition." The Tacoma Narrows Bridge is still one of the best-maintained bridges in the country.
Today, this bridge serves as the westbound span across the Narrows.
Construction Safety
Building the 1950 Tacoma Narrows Bridge was a big and challenging project. Sadly, some workers were hurt or lost their lives during its construction.
- On May 24, 1948, Robert E. Drake was working on cables at the west anchorage. A cable on a derrick broke, and the boom fell on him.
- On April 7, 1950, Lawrence S. Gale, an ironworker, was working on the stiffening truss. He noticed a weld that looked wrong and was going to fix it when it broke. He fell 120 feet (37 m) into the Narrows, along with 40 short tons (36 t) of steel.
- On June 6, 1950, workers were putting in temporary wooden beams for concrete trucks. One worker stepped onto a new section of timbers and missed, falling into the water below.
- On July 31, 1950, a welder named Ray Bradley was working on an expansion joint. It was raining heavily, and he reached for a welding wire. He suffered a heart attack, though some workers thought it might have been from electrocution.
- Bridging the Narrows, Joe Gotchy (1990), Gig Harbor Peninsula Historical Society, (ISBN: 0-9626048-1-X)
- Catastrophe to Triumph: The Bridges of the Tacoma Narrows. Richard S. Hobbs (2006) WSU Press. (ISBN: 0-87422-289-3)
- Masters of Suspension: The men and women who bridged the Tacoma Narrows again. Rob Carson/Dean J. Koepfler (2007) The News Tribune (ISBN: 978-0-9633035-2-3)
See also
In Spanish: Puente de Tacoma (1950) para niños
