.gif)
Tacoma Narrows Bridge (1950)
Encyclopedia
The 1950 Tacoma Narrows Bridge is a suspension bridge
in the U.S.
state of Washington that carries the westbound lanes of Washington State Route 16 (known as Primary State Highway 14 until 1964) across the Tacoma Narrows
strait, between the city of Tacoma
and the Kitsap Peninsula
. Opened on October 14, 1950, it was built in the same location as the original Tacoma Narrows Bridge
, which collapsed due to a windstorm on November 7, 1940. It is the older of the twin bridges
that make up the Tacoma Narrows Bridge
crossing of the Tacoma Narrows, and carried both directions of traffic across the strait until 2007. At the time of its construction, the bridge was, like its predecessor, the third-longest suspension bridge in the world in terms of main span length, behind the Golden Gate Bridge
and George Washington Bridge
; it is now the 31st longest suspension bridge in the world.
Design work on a new Tacoma Narrows Bridge began shortly after the collapse of the original bridge. However, several engineering issues, the demand on steel created by the United States' involvement in World War II
, and the state of Washington's inability to find an insurer, all pushed the start of construction to April 1948. The new bridge was designed with a wider deck and taller and wider towers than its predecessor, and addressed the wind issues that led to the original bridge's collapse. It opened to the public on October 14, 1950, and carried both directions of Primary State Highway 14 for over 40 years. Tolls
were charged on the bridge until 1965, 13 years ahead of schedule.
By 1990, population growth and development on the Kitsap Peninsula caused vehicular traffic on the bridge to exceed its design capacity. In 1998, voters in several Washington counties approved an advisory measure to create a twin bridge to span the Tacoma Narrows. After a series of protests and court battles, construction began on the second span in 2002. The second span opened in July 2007 to carry eastbound traffic, and the 1950 bridge was reconfigured to carry westbound traffic.
appointed Charles E. Andrew (who had been involved in Gertie's design and construction as a consultant) as principal engineer and chairman of the consulting board in charge of designing a new span across the Narrows. Members of the new design board included Dr. Theodore von Kármán
, Glenn Woodruff, and the firm of Sverdrup and Parcel of Chicago, Illinois. To lead the design team, Andrew picked Dexter R. Smith as lead designer and principal architect. As early as October 1941, less than a year after Gertie's collapse, the WTBA had adopted a rough design for a new span. The new design closely resembled the original design for the 1940 span drawn up by Clark Eldridge
. The cost of construction on the new design was then estimated at $7 million (US$
in present terms).
Since the original bridge became a major asset in the short time it was in service, the U.S. Navy lobbied heavily for a combination highway/railroad span across the Narrows to replace Gertie, and proposed a steel
-cantilever
-type bridge over a suspension span. However, the extra steel needed to construct such a structure across the Narrows would have added an extra $8.5 million (US$
in present terms) to the construction cost, ruling out any possibility of such a structure ever being built.
Furthermore, the proposed design needed new testing. A purely mathematical solution to designing suspension spans was not possible because little was known about the forces that brought down Gertie. In light of that fact, engineers chose to design the replacement, then subject scale mockups of the design in a specially-built wind tunnel constructed at the University of Washington. According to Charles Andrew, "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." The testing was performed by Professor F. B. Farquharson, who had researched Gertie's motions prior to its collapse on November 7, 1940.
From late 1941 onward, Professor Farquharson (as well as von Karman, who did his work at the California Institute of Technology
in Pasadena, California
) continued to work on the new bridge design. By 1943, he was working in a specially-designed wind tunnel laboratory built on the University of Washington campus in Seattle. The facility was large enough to house a scale model of the completed bridge as long as 100 feet (30.5 m), plus section models for further testing. After Farquharson confirmed that Gertie collapsed due to its excessive flexibility and the aerodynamic forces as a result of the flexibility in her span, testing was then done on designs drawn by Smith. All of the new designs would feature a deep open stiffening truss
instead of a solid plate girder.
Testing on the new bridge design was begun in November 1943 and continued through 1945. The studies included 200 different configurations, to wind forces hitting the span at up to plus-or-minus 45-degrees perpendicular to the deck. Then, testing was performed on a design using open strips of wind grating placed in the roadway, which added even greater stability against torsional movement. A design with bottom lateral bracing on the stiffening truss was also tested to test the resistance against lateral movement. Then, a design was tested with motion dampening devices located on the deck at three locations: one at each tower (one at each end of the main span, and one on each side span at the tower), and a set of dampening devices at mid-span on each main cable. Each of these steps in the design and testing phase were performed to reduce as much lateral and torsional movement as possible.
After $80,000 (US$
in present terms) was spent in the design and testing of the new span, the design was completed on December 5, 1945. The WTBA finalized and approved revised designs from Dexter's drawings in December in April, 1946, and minor revisions continued on until September. The new span was to have a construction cost of $8.5 million (US$
in present terms).
The final designs of the Tacoma Narrows Bridge, once finalized, were a sharp and drastic contrast from the design by Leon Moisseiff
. Instead of a thin plate girder, an open-air stiffening truss with a depth of 33 feet (10.1 m) would form the new road deck. Newer, larger towers that rose 58 feet (17.7 m) higher and 21 feet (6.4 m) wider than Gertie's towers, would support the bridge's main cables, now 20+1/4 in in diameter versus Gertie's 17+1/2 in. Newer, larger anchor blocks would support a load that weighed 1.6 times as much as the original bridge. However, some elements of Galloping Gertie were incorporated into the 1950 span. The tower pedestals were enlarged and raised 17 feet (5.2 m). On the west end stood a 450 feet (137.2 m) long approach viaduct with the same 8 feet (2.4 m) deep girders Gertie's main deck had. This approach viaduct used three support towers, two with thin support beams and one with the structural complexity and design of one of Gertie's main towers - each spaced 150 feet (45.7 m) apart. The viaduct, after a structural examination, was kept and utilized as part of the 1950 bridge's design, with an additional box strut brace added to the tower closest the shoreline (officially known as Tower #3 in the design plans), and widening of the upper box strut for the new bridge's deck.
The road deck itself was seen as a major innovation in suspension bridge design. Lanes of traffic on typical suspension bridge roadways are divided by dashed paint lines, a solid strip, or a set of two strips of paint. On the 1950 span's final roadway design, the 46 feet (14 m)-wide roadway was split into four lanes of traffic, each lane being 9+5/8 ft wide. Each lane was separated by a 3 inches (7.6 cm) deep, 33 inches (83.8 cm)-wide open air wind grate. Bordering the outside lanes was a 19 inches (48.3 cm) open air wind grate that supported a 5 inches (12.7 cm) pipe curb elevated 1 foot (0.3048 m) off the roadway. These also formed the separation between the roadway, and a 3 foot (0.9144 m)-wide sidewalk on both sides that was fenced in by a 4 feet (1.2 m)-high railing.
in present terms) to $11.2 million (US$
in present terms). On October 15, the state opened bids for the construction, with Bethlehem Pacific Steel Corporation bidding $8,263,904 (US$
in present terms) on construction of the superstructure, and John A. Roebling's Sons Company of San Francisco bidding $2,932,681 (US$
in present terms) for the construction of the suspension cable system.
After several delays involving final financing, the WTBA finally offered a $14 million (US$
in present terms) bond that was to be repaid via tolls on the bridge, as well as Pierce County offering a $1.5 million (US$
in present terms) bond guarantee fund. On March 12, 1948 the state finally completed bond financing. And after steel became more readily available, the puzzle pieces began falling together in rapid fashion. The construction contracts were finally awarded on March 31, and April 1, and by April 9, earth moving began at the remains of Gertie's east cable anchorage. Construction progressed rather rapidly on the new span once earth moving began.
The tower pedestals had creosote timber fenders, which were installed in 1948 to deflect marine debris and traffic, which were removed sometime between 1995 and 2000.
The tower pedestals that supported Gertie's towers were found to be structurally sound and unharmed after the failure of that span, and were reused for the current bridge. The towers of the 1940 span in their short service time experienced corrosion from salt water spray at their bases, so engineers constructed new tops to the pedestals, at the same time the anchorages were being built, to allow for tower construction to begin in near unison. The new tower pedestals (called piers in the designs) were raised 17 feet (5.2 m) to prevent the corrosion issue, and were enlarged where the towers would stand to provide more structural rigidity. The east and west piers were completed in mid-December 1948.
measuring 7.1 rattled the Puget Sound region. The earthquake
caused the towers to sway 6 feet (1.8 m) from vertical, causing the cable saddle to shear its bolts and fall off the tower http://earthquake.usgs.gov/regional/states/events/1949_04_13.phphttp://www.wsdot.wa.gov/TNBhistory/weirdfacts.htmhttp://www.thenewstribune.com/937/story/79137.html. The saddle fell 510 feet (155.4 m) below. It missed the pedestal, and plunged straight through a barge, to a final resting spot 135 feet (41.1 m) below the surface of the Narrows, 75 feet (22.9 m) away from the pedestal. The resulting impact sank the barge, taking a compressor and numerous other tools with it. Divers soon located the cable saddle in a deep hole during a slack tide (the only time divers could operate, and slack tides only occurred at night). After a three-day delay, it was raised to the surface, repaired (the impact bent a corner on it), and reinstalled. The earthquake delayed completion of both the east and west towers on the bridge. After the earthquake's aftershocks subsided, work resumed, and by July 17 both towers were announced as being completed.
Construction of the main cables began by erecting their 10 feet (3 m) wide catwalks in July. On July 17, 1949, the first catwalk line was towed via tugboat across the Narrows, then lifted onto the towers. The catwalks, consisting of 1 inches (2.5 cm) diameter wire base cables, cyclone-wire fencing, and a 4 feet (1.2 m) center section of wood slats, were erected in 200 feet (61 m) sections. On September 15, the catwalks were completed and the spinning gear was in place. Harold Hills, a field engineer for Roebling's Sons Company, became the first man to cross the Narrows via the catwalks. On the following day, Harry Cornelius, an inspector for the WTBA became the second to cross the Narrows on the catwalks.
To begin preparations for spinning the main cables, Roebling's Sons had set up a reeling plant on the Tacoma tideflats. 100000000 feet (30,480,000 m) of galvanized steel wire - the total amount needed for both main cables, began arriving in 350 pounds (158.8 kg) coils. Shipped in from Trenton, New Jersey
, these coils were then transferred to intermediate reels, then wound onto a final reel of steel wire that held it at uniform tension. Each 8 feet (2.4 m) diameter reel of wire weighed 9 short tons (8 LT), and contained 36 miles (57.9 km) of wire.
October 13, the guide wires for cable operations were installed, and cable spinning operations began. 19 cable strands, each carrying 458 number 6-gauge steel wire comprised the main suspension cables (a total of 8,705 per cable). The first strand to be completed was a cable strand on the north cable, on October 26. Working three shifts 24 hours per day, Roebling's Sons were delayed a few times due to weather and high winds. On January 16, 1950, amidst one of the worst winters in local record, workers completed the main cables. Cable band placement and vertical suspender cable installation was complete by March 7, and deck construction began almost immediately.
Construction of the new road deck and stiffening truss of the 1950 span was conducted differently than had been done in Gertie's case. In 1940, the road deck was prefabricated in 100 feet (30.5 m) long sections on the Tacoma tideflats, then barged to the site via tugboats and hoisted into place via gantry cranes installed on the main cable. When construction of the road deck began in early March, workers installed a Chicago boom high above the roadway level, upon which prefabricated stiffening truss assemblies each 32 feet (9.8 m)-by-60 feet (18.3 m) were hoisted into place. After the deck assemblies were hoisted into place and finished, four traveling derricks were then lifted onto the completed deck sections. After the traveling derricks (called "layleg rigs" by the crew) were assembled and readied, the deck was then assembled in a series of steps. On the new bridge, the stiffening truss featured a series of outer members called "chords" that formed the top and bottom of the stiffening truss. These were installed first, then the diagonal and vertical truss members on the sides were installed. Next, an 11 feet (3.4 m) deep stiffening truss "floor beam" perpendicular to the length of the bridge was installed at intervals of 32 feet (9.8 m) (the distance between suspender cables; they were installed at each vertical beam member in the stiffening truss). These floor beams, each 60 feet (18.3 m) wide, would form the upper lateral stiffening mechanism in the deck itself. After the floor beams were installed, at alternate floor beam panel points a set of diagonal bracing struts were installed. Then, a series of lateral bracing struts were installed on the top and bottom of the road deck - that connected to the outer steel chords. Next, a series of eight 18 inches (45.7 cm) deep I-beam "stringers" were installed (positioned longitudinally). This was the final steelwork step involved, and the deck was soon raised 1 in 6 in (0.4572 m) on each corner to attach the suspender cables and their "jewels" to the vertical stiffening truss members.
Unlike Gertie, whose preassembled deck sections were first raised into place at the center of the main span and the ends of the sidespans, on the new bridge the stiffening truss was erected first at each tower, and then progressed outwards. Four work crews, one on each side span and two on the main span (one each side) worked together completing each step in 64 feet (19.5 m) intervals (completing an average of 128 feet (39 m) of steelwork per day). The side span crews worked towards shore and the main span crews worked towards each other, and by May 1949, work was nearing completion. On May 28, ironworkers installed the closing top chord on the main span, and over the next two days workers finished closing the span up. On June 1, the steel stiffening truss of the road deck was declared complete.
Work also progressed at the west end of the bridge, where workers modified the 450 feet (137.2 m) long approach viaduct that once had been a part of the 1940 span for use in the 1950 bridge. There, workers added bracing and brackets that would widen the viaduct from 39 feet (11.9 m), to accommodate the widened roadway width of 48 feet (14.6 m).
Traffic counts following the opening day ceremonies steadily rose in the first few years, just as they had in the four months Gertie was in service. Five years after the bridge opened, the average count was 4,699 vehicles per day. By 1960, an average of 6,218 vehicles crossed, and in 1965, fifteen years after the bridge opened, the figure from 1960 was doubled. With an average of 11,267 vehicles per day, the Washington Toll Bridge Authority soon removed the tolls. In early 1965, a bill passed the state legislature removing the tolls, and on May 14, 1965, in a ceremony at the toll plaza, Governor Dan Evans signed the legislation that removed the tolls. The signing was significant and historic. Significant because the bridge had been paid off - the accrued revenue stood at $19 million (US$
in present terms) - $5 million (US$
in present terms) more than the construction bond's cost and accrued interest. It was also historic, because the tolls were removed 13 years ahead of schedule.
The bridge has also survived several major earthquakes since its completion. The first earthquake occurred during construction on April 13, 1949, and knocked the north cable's 21 short tons (18.7 LT) steel saddle from the east tower. Another strong earthquake struck the region on April 29, 1965. In 1999 a series of moderate earthquakes struck the region, and the most recent earthquake is the 2001 Nisqually Earthquake. Even though the bridge escaped damage in all of those earthquakes, the 1949 earthquake still has a lasting legacy hold on the span. As a result of the north cable saddle's plunge from the east tower, and resulting three-day stay in 135 feet of salt water, it now corrodes more than twice as fast as its counterparts.
On the bridge's 50th anniversary in 2000, a private firm that inspected the span concluded that "it is one of the best for its maintenance and condition" and overall, the Tacoma Narrows Bridge remains one of the best maintained spans in the nation.
Today, the bridge currently serves as the westbound span over the Narrows.
Suspension bridge
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. Outside Tibet and Bhutan, where the first examples of this type of bridge were built in the 15th century, this type of bridge dates from the early 19th century...
in the U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
state of Washington that carries the westbound lanes of Washington State Route 16 (known as Primary State Highway 14 until 1964) across the Tacoma Narrows
Tacoma Narrows
The Tacoma Narrows , a strait, is part of Puget Sound in the U.S. state of Washington. A navigable maritime waterway between glacial landforms, the Narrows separates the Kitsap Peninsula from the city of Tacoma....
strait, between the city of Tacoma
Tacoma, Washington
Tacoma is a mid-sized urban port city and the county seat of Pierce County, Washington, United States. The city is on Washington's Puget Sound, southwest of Seattle, northeast of the state capital, Olympia, and northwest of Mount Rainier National Park. The population was 198,397, according to...
and the Kitsap Peninsula
Kitsap Peninsula
The Kitsap Peninsula is an arm of land that is part of the larger Olympic Peninsula in Washington state that lies west of Seattle across Puget Sound. Hood Canal separates Kitsap Peninsula from the rest of the Olympic Peninsula...
. Opened on October 14, 1950, it was built in the same location as the original Tacoma Narrows Bridge
Tacoma Narrows Bridge (1940)
The 1940 Tacoma Narrows Bridge was the first incarnation of the Tacoma Narrows Bridge, a suspension bridge in the U.S. state of Washington that spanned the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula. It opened to traffic on July 1, 1940, and dramatically collapsed...
, which collapsed due to a windstorm on November 7, 1940. It is the older of the twin bridges
Twin bridges
Twin bridges are a set of two bridges running parallel to each other. A pair of twin bridges is often referred to collectively as a twin-span or dual-span bridge. Bridges of this type are often created by building a new bridge parallel to an existing one in order to increase the traffic capacity...
that make up the Tacoma Narrows Bridge
Tacoma Narrows Bridge
The Tacoma Narrows Bridge is a pair of twin suspension bridges in the U.S. state of Washington, which carry State Route 16 across the Tacoma Narrows strait of Puget Sound between Tacoma and the Kitsap Peninsula...
crossing of the Tacoma Narrows, and carried both directions of traffic across the strait until 2007. At the time of its construction, the bridge was, like its predecessor, the third-longest suspension bridge in the world in terms of main span length, behind the Golden Gate Bridge
Golden Gate Bridge
The Golden Gate Bridge is a suspension bridge spanning the Golden Gate, the opening of the San Francisco Bay into the Pacific Ocean. As part of both U.S. Route 101 and California State Route 1, the structure links the city of San Francisco, on the northern tip of the San Francisco Peninsula, to...
and George Washington Bridge
George Washington Bridge
The George Washington Bridge is a suspension bridge spanning the Hudson River, connecting the Washington Heights neighborhood in the borough of Manhattan in New York City to Fort Lee, Bergen County, New Jersey. Interstate 95 and U.S. Route 1/9 cross the river via the bridge. U.S...
; it is now the 31st longest suspension bridge in the world.
Design work on a new Tacoma Narrows Bridge began shortly after the collapse of the original bridge. However, several engineering issues, the demand on steel created by the United States' involvement in World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, and the state of Washington's inability to find an insurer, all pushed the start of construction to April 1948. The new bridge was designed with a wider deck and taller and wider towers than its predecessor, and addressed the wind issues that led to the original bridge's collapse. It opened to the public on October 14, 1950, and carried both directions of Primary State Highway 14 for over 40 years. Tolls
Toll bridge
A toll bridge is a bridge over which traffic may pass upon payment of a toll, or fee.- History :The practice of collecting tolls on bridges probably harks back to the days of ferry crossings where people paid a fee to be ferried across stretches of water. As boats became impractical to carry large...
were charged on the bridge until 1965, 13 years ahead of schedule.
By 1990, population growth and development on the Kitsap Peninsula caused vehicular traffic on the bridge to exceed its design capacity. In 1998, voters in several Washington counties approved an advisory measure to create a twin bridge to span the Tacoma Narrows. After a series of protests and court battles, construction began on the second span in 2002. The second span opened in July 2007 to carry eastbound traffic, and the 1950 bridge was reconfigured to carry westbound traffic.
Design
The designs for the 1950 Tacoma Narrows Bridge were drawn up not long after the 1940 collapse of its predecessor. In July, 1941, the Washington Toll Bridge AuthorityWashington Toll Bridge Authority
The Washington Toll Bridge Authority was created in 1937 by the Washington State Legislature, with a mandate to finance, construct and operate toll bridges....
appointed Charles E. Andrew (who had been involved in Gertie's design and construction as a consultant) as principal engineer and chairman of the consulting board in charge of designing a new span across the Narrows. Members of the new design board included Dr. Theodore von Kármán
Theodore von Karman
Theodore von Kármán was a Hungarian-American mathematician, aerospace engineer and physicist who was active primarily in the fields of aeronautics and astronautics. He is responsible for many key advances in aerodynamics, notably his work on supersonic and hypersonic airflow characterization...
, Glenn Woodruff, and the firm of Sverdrup and Parcel of Chicago, Illinois. To lead the design team, Andrew picked Dexter R. Smith as lead designer and principal architect. As early as October 1941, less than a year after Gertie's collapse, the WTBA had adopted a rough design for a new span. The new design closely resembled the original design for the 1940 span drawn up by Clark Eldridge
Clark Eldridge
Clark Eldridge was one of the engineers who designed the first Tacoma Narrows Bridge.In 1936, Eldridge joined the Washington State Highway Department. He designed two of the state's most colossal bridges, the Lake Washington Floating Bridge and the first Tacoma Narrows Bridge...
. The cost of construction on the new design was then estimated at $7 million (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms).
Since the original bridge became a major asset in the short time it was in service, the U.S. Navy lobbied heavily for a combination highway/railroad span across the Narrows to replace Gertie, and proposed a steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
-cantilever
Cantilever
A cantilever is a beam anchored at only one end. The beam carries the load to the support where it is resisted by moment and shear stress. Cantilever construction allows for overhanging structures without external bracing. Cantilevers can also be constructed with trusses or slabs.This is in...
-type bridge over a suspension span. However, the extra steel needed to construct such a structure across the Narrows would have added an extra $8.5 million (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms) to the construction cost, ruling out any possibility of such a structure ever being built.
Furthermore, the proposed design needed new testing. A purely mathematical solution to designing suspension spans was not possible because little was known about the forces that brought down Gertie. In light of that fact, engineers chose to design the replacement, then subject scale mockups of the design in a specially-built wind tunnel constructed at the University of Washington. According to Charles Andrew, "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." The testing was performed by Professor F. B. Farquharson, who had researched Gertie's motions prior to its collapse on November 7, 1940.
From late 1941 onward, Professor Farquharson (as well as von Karman, who did his work at the California Institute of Technology
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...
in Pasadena, California
Pasadena, California
Pasadena is a city in Los Angeles County, California, United States. Although famous for hosting the annual Rose Bowl football game and Tournament of Roses Parade, Pasadena is the home to many scientific and cultural institutions, including the California Institute of Technology , the Jet...
) continued to work on the new bridge design. By 1943, he was working in a specially-designed wind tunnel laboratory built on the University of Washington campus in Seattle. The facility was large enough to house a scale model of the completed bridge as long as 100 feet (30.5 m), plus section models for further testing. After Farquharson confirmed that Gertie collapsed due to its excessive flexibility and the aerodynamic forces as a result of the flexibility in her span, testing was then done on designs drawn by Smith. All of the new designs would feature a deep open stiffening truss
Truss
In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in...
instead of a solid plate girder.
Testing on the new bridge design was begun in November 1943 and continued through 1945. The studies included 200 different configurations, to wind forces hitting the span at up to plus-or-minus 45-degrees perpendicular to the deck. Then, testing was performed on a design using open strips of wind grating placed in the roadway, which added even greater stability against torsional movement. A design with bottom lateral bracing on the stiffening truss was also tested to test the resistance against lateral movement. Then, a design was tested with motion dampening devices located on the deck at three locations: one at each tower (one at each end of the main span, and one on each side span at the tower), and a set of dampening devices at mid-span on each main cable. Each of these steps in the design and testing phase were performed to reduce as much lateral and torsional movement as possible.
After $80,000 (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms) was spent in the design and testing of the new span, the design was completed on December 5, 1945. The WTBA finalized and approved revised designs from Dexter's drawings in December in April, 1946, and minor revisions continued on until September. The new span was to have a construction cost of $8.5 million (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms).
Leon Moisseiff
Leon S. Moisseiff was a leading suspension bridge engineer in the United States of America in the 1920s and 1930s. He was awarded The Franklin Institute's Louis E...
. Instead of a thin plate girder, an open-air stiffening truss with a depth of 33 feet (10.1 m) would form the new road deck. Newer, larger towers that rose 58 feet (17.7 m) higher and 21 feet (6.4 m) wider than Gertie's towers, would support the bridge's main cables, now 20+1/4 in in diameter versus Gertie's 17+1/2 in. Newer, larger anchor blocks would support a load that weighed 1.6 times as much as the original bridge. However, some elements of Galloping Gertie were incorporated into the 1950 span. The tower pedestals were enlarged and raised 17 feet (5.2 m). On the west end stood a 450 feet (137.2 m) long approach viaduct with the same 8 feet (2.4 m) deep girders Gertie's main deck had. This approach viaduct used three support towers, two with thin support beams and one with the structural complexity and design of one of Gertie's main towers - each spaced 150 feet (45.7 m) apart. The viaduct, after a structural examination, was kept and utilized as part of the 1950 bridge's design, with an additional box strut brace added to the tower closest the shoreline (officially known as Tower #3 in the design plans), and widening of the upper box strut for the new bridge's deck.
The road deck itself was seen as a major innovation in suspension bridge design. Lanes of traffic on typical suspension bridge roadways are divided by dashed paint lines, a solid strip, or a set of two strips of paint. On the 1950 span's final roadway design, the 46 feet (14 m)-wide roadway was split into four lanes of traffic, each lane being 9+5/8 ft wide. Each lane was separated by a 3 inches (7.6 cm) deep, 33 inches (83.8 cm)-wide open air wind grate. Bordering the outside lanes was a 19 inches (48.3 cm) open air wind grate that supported a 5 inches (12.7 cm) pipe curb elevated 1 foot (0.3048 m) off the roadway. These also formed the separation between the roadway, and a 3 foot (0.9144 m)-wide sidewalk on both sides that was fenced in by a 4 feet (1.2 m)-high railing.
Construction
Constructing the replacement Tacoma Narrows Bridge was delayed for nearly a decade primarily due to the demand on steel created by World War II, and the fact that the state had trouble arranging insurance for the new span. On April 30, 1947, Governor Mon Wallgren had announced that insurance had finally been arranged. It wasn't until August 1947 that Washington finally requested bids for the construction, and by that time, the price tag for construction went from $8.5 million (US$United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms) to $11.2 million (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms). On October 15, the state opened bids for the construction, with Bethlehem Pacific Steel Corporation bidding $8,263,904 (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms) on construction of the superstructure, and John A. Roebling's Sons Company of San Francisco bidding $2,932,681 (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms) for the construction of the suspension cable system.
After several delays involving final financing, the WTBA finally offered a $14 million (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms) bond that was to be repaid via tolls on the bridge, as well as Pierce County offering a $1.5 million (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms) bond guarantee fund. On March 12, 1948 the state finally completed bond financing. And after steel became more readily available, the puzzle pieces began falling together in rapid fashion. The construction contracts were finally awarded on March 31, and April 1, and by April 9, earth moving began at the remains of Gertie's east cable anchorage. Construction progressed rather rapidly on the new span once earth moving began.
Anchorages
Since the replacement span was going to be 1.6 times heavier than the bridge it replaced, as well as four lanes instead of two, modification and partial demolition was necessary to begin construction on the newer, and much more massive cable anchorages at each end of the bridge. The center of the old anchorages were kept as cores, and a newer eyebar system set at 60 feet (18.3 m) apart (versus 39 feet (11.9 m) for the previous bridge) were constructed. They would support a much larger cable load from the original 28000000 pounds (12,700,586.4 kg) to a much heavier 36000000 pounds (16,329,325.3 kg), and consisted of steel eyebars 62 feet (18.9 m) long, with 26 inches (66 cm) diameter shoes, embedded into new concrete. Each new anchor would weigh 54000 short tons (48,214.1 LT) and would be embedded deep into compacted soil. Construction of the new cable anchorages was performed during the summer of 1948 and continued into late 1948 and into 1949.Tower pedestals
Due to the 150 foot water depth of the narrows, the Tower Pedestals are each the size of a 20 story office building, with an overall size of 130 x 80 x 225 feet, upon rests the 510 foot towers. They are designed to withstand daily 7 knot currents and a twice daily 15 foot tidal swing. Each tower pedestal used 34,000 cubic yards of concrete for construction.The tower pedestals had creosote timber fenders, which were installed in 1948 to deflect marine debris and traffic, which were removed sometime between 1995 and 2000.
The tower pedestals that supported Gertie's towers were found to be structurally sound and unharmed after the failure of that span, and were reused for the current bridge. The towers of the 1940 span in their short service time experienced corrosion from salt water spray at their bases, so engineers constructed new tops to the pedestals, at the same time the anchorages were being built, to allow for tower construction to begin in near unison. The new tower pedestals (called piers in the designs) were raised 17 feet (5.2 m) to prevent the corrosion issue, and were enlarged where the towers would stand to provide more structural rigidity. The east and west piers were completed in mid-December 1948.
Towers
The original towers for the 1940 Tacoma Narrows Bridge featured four deep, box-shaped struts (two below the roadway and two above), as well as being tapered from being 50 feet (15.2 m) wide at the base to 39 feet (11.9 m) at the top. The new towers of the replacement span were to be the same width both at the bottom and the top, and were to feature a deep X-bracing system with three 45 feet (13.7 m)-deep single X-brace struts below the road deck and a series of three double-X brace struts of varying depths above the roadway (top being 23 inch, middle being 24 inch, and the bottom being 26 inch). Tower construction began January 1, 1949, and progressed rapidly. Work went ahead of schedule and by April 1949, the 21 short tons (18.7 LT) steel cable saddles were prepared for lifting. On April 13, 1949, the north cable saddle on the east tower was bolted into place on a set of shims to allow workers to rivet the top plate into place. Then, disaster struck. That morning, an earthquakeEarthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
measuring 7.1 rattled the Puget Sound region. The earthquake
1949 Olympia Earthquake
The 1949 Olympia earthquake occurred on April 13, 1949 at 19:55 UTC , and is the largest recorded earthquake to occur in the Puget Sound region of Washington, with a magnitude of 7.1....
caused the towers to sway 6 feet (1.8 m) from vertical, causing the cable saddle to shear its bolts and fall off the tower http://earthquake.usgs.gov/regional/states/events/1949_04_13.phphttp://www.wsdot.wa.gov/TNBhistory/weirdfacts.htmhttp://www.thenewstribune.com/937/story/79137.html. The saddle fell 510 feet (155.4 m) below. It missed the pedestal, and plunged straight through a barge, to a final resting spot 135 feet (41.1 m) below the surface of the Narrows, 75 feet (22.9 m) away from the pedestal. The resulting impact sank the barge, taking a compressor and numerous other tools with it. Divers soon located the cable saddle in a deep hole during a slack tide (the only time divers could operate, and slack tides only occurred at night). After a three-day delay, it was raised to the surface, repaired (the impact bent a corner on it), and reinstalled. The earthquake delayed completion of both the east and west towers on the bridge. After the earthquake's aftershocks subsided, work resumed, and by July 17 both towers were announced as being completed.
Cables
To begin preparations for spinning the main cables, Roebling's Sons had set up a reeling plant on the Tacoma tideflats. 100000000 feet (30,480,000 m) of galvanized steel wire - the total amount needed for both main cables, began arriving in 350 pounds (158.8 kg) coils. Shipped in from Trenton, New Jersey
Trenton, New Jersey
Trenton is the capital of the U.S. state of New Jersey and the county seat of Mercer County. As of the 2010 United States Census, Trenton had a population of 84,913...
, these coils were then transferred to intermediate reels, then wound onto a final reel of steel wire that held it at uniform tension. Each 8 feet (2.4 m) diameter reel of wire weighed 9 short tons (8 LT), and contained 36 miles (57.9 km) of wire.
October 13, the guide wires for cable operations were installed, and cable spinning operations began. 19 cable strands, each carrying 458 number 6-gauge steel wire comprised the main suspension cables (a total of 8,705 per cable). The first strand to be completed was a cable strand on the north cable, on October 26. Working three shifts 24 hours per day, Roebling's Sons were delayed a few times due to weather and high winds. On January 16, 1950, amidst one of the worst winters in local record, workers completed the main cables. Cable band placement and vertical suspender cable installation was complete by March 7, and deck construction began almost immediately.
Stiffening truss
Unlike Gertie, whose preassembled deck sections were first raised into place at the center of the main span and the ends of the sidespans, on the new bridge the stiffening truss was erected first at each tower, and then progressed outwards. Four work crews, one on each side span and two on the main span (one each side) worked together completing each step in 64 feet (19.5 m) intervals (completing an average of 128 feet (39 m) of steelwork per day). The side span crews worked towards shore and the main span crews worked towards each other, and by May 1949, work was nearing completion. On May 28, ironworkers installed the closing top chord on the main span, and over the next two days workers finished closing the span up. On June 1, the steel stiffening truss of the road deck was declared complete.
Final deckwork and construction
Throughout the summer of 1950, as many as 200 men were involved in the final steps of completion of the 1950 Tacoma Narrows Bridge. On July 24, workers from Roebling's Sons were involved in wrapping and caulking the suspender cable bands, and the railings on the sidewalks were being completed. By August 22, the road deck was taking shape, as workers continued concrete pours for the roadway. Painting began that week, as eleven men worked the paint crew sandblasting and painting the stiffening truss. The bridge received its first coat of "Narrows Green" paint - a grayish-green hue (its predecessor had been painted the same color a decade before). By September 30, workers installed the finishing touches on the toll plazas, including installing sheetrock and plumbing. The midspan and tower hydraulic dampening mechanisms were also installed, and workers began removing the catwalks, tower buttresses, and other working platforms.Work also progressed at the west end of the bridge, where workers modified the 450 feet (137.2 m) long approach viaduct that once had been a part of the 1940 span for use in the 1950 bridge. There, workers added bracing and brackets that would widen the viaduct from 39 feet (11.9 m), to accommodate the widened roadway width of 48 feet (14.6 m).
Opening
The bridge opened to toll-paid traffic on October 14, 1950. The opening day tolls were fifty cents one way per car and driver, and an additional ten cents per passenger. Thousands attended opening day ceremonies, including Governor Arthur B. Langlie. A commemorative phamplet published by the Tacoma News Tribune was distributed, as well as scores of speeches given. After 30 months of construction, the Narrows was bridged again.Traffic counts following the opening day ceremonies steadily rose in the first few years, just as they had in the four months Gertie was in service. Five years after the bridge opened, the average count was 4,699 vehicles per day. By 1960, an average of 6,218 vehicles crossed, and in 1965, fifteen years after the bridge opened, the figure from 1960 was doubled. With an average of 11,267 vehicles per day, the Washington Toll Bridge Authority soon removed the tolls. In early 1965, a bill passed the state legislature removing the tolls, and on May 14, 1965, in a ceremony at the toll plaza, Governor Dan Evans signed the legislation that removed the tolls. The signing was significant and historic. Significant because the bridge had been paid off - the accrued revenue stood at $19 million (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms) - $5 million (US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
in present terms) more than the construction bond's cost and accrued interest. It was also historic, because the tolls were removed 13 years ahead of schedule.
Traffic increases
For the first few decades after its opening, traffic congestion was no issue. Off of the west end of the bridge, Highway 16 (until 1964, it was signed as Primary State Highway 14-PT) transformed from a four-lane freeway to a narrow two-lane country highway. By the late 1980s, as developers began constructing housing and shopping mall projects in Gig Harbor, Highway 16 was expanded and realigned from a meandering two-lane country road to a four-lane freeway that stretched from Tacoma to Gorst. As a result, traffic congestion grew enough to where backups began occurring. In 1980, average counts were at 38,973 vehicles per day. In 1990, the figure doubled to 66,573, 6,573 more than its designed daily capacity. Many of the backups on the bridge occurred on the east end as workers from Tacoma headed towards their homes in Gig Harbor, and those backups would stretch as far as Interstate-5 nearly 6 miles (9.7 km) away. The backups were also mentioned in a book published by ironworker Joe Gotchy in 1990, titled "Bridging the Narrows." These backups continued to get worse, and by 2000, the average daily count of traffic on the Tacoma Narrows Bridge was 88,000. This prompted the state legislature to call an advisory vote to build a new span across the Narrows. After a series of protests, both inside and outside of the courtroom, it was made official on October 5, 2002 as groundbreaking occurred for the new bridge.Lasting legacy on bridge design
The failure of the 1940 Tacoma Narrows Bridge and the design of the 1950 Tacoma Narrows Bridge led to a number of firsts in suspension bridge design. The 1950 bridge was the first to be designed and tested in wind tunnels, and was the first suspension bridge designed and built with hydraulic motion dampening devices.Maintenance, and the bridge today
The 1950 Tacoma Narrows Bridge undergoes a rigorous maintenance schedule that is a year-long effort. Maintenance crews often perform replacement of steel parts, and inspect the steel cables and towers at night or at low traffic hours. Painting the bridge is also a drawn-out task. Working only during the summer months, it takes ten years to paint the span. The color of the bridge is officially known as "Narrows Green", a grayish-green hue that was the original color of the ill-fated 1940 span (called Chrome Green in a 1940 newspaper report on the final stages of Gertie's construction).The bridge has also survived several major earthquakes since its completion. The first earthquake occurred during construction on April 13, 1949, and knocked the north cable's 21 short tons (18.7 LT) steel saddle from the east tower. Another strong earthquake struck the region on April 29, 1965. In 1999 a series of moderate earthquakes struck the region, and the most recent earthquake is the 2001 Nisqually Earthquake. Even though the bridge escaped damage in all of those earthquakes, the 1949 earthquake still has a lasting legacy hold on the span. As a result of the north cable saddle's plunge from the east tower, and resulting three-day stay in 135 feet of salt water, it now corrodes more than twice as fast as its counterparts.
On the bridge's 50th anniversary in 2000, a private firm that inspected the span concluded that "it is one of the best for its maintenance and condition" and overall, the Tacoma Narrows Bridge remains one of the best maintained spans in the nation.
Today, the bridge currently serves as the westbound span over the Narrows.