Friday, July 31, 2009

New York City's Bridges: High Bridge

The High Bridge was originally a stone masonry aqueduct that was completed in 1848. It consisted of fifteen arches that carried two cast iron pipes across the Harlem River Valley at 174th Street. It was designed by John B. Jervis and closely resembled the Puente Trajan in Spain that was built around 110 A.D. A third pipe and a walkway was added in 1864.

By 1920, a channel had been built around Manhattan and the aqueduct was to be removed as an obstacle to navigation. After considerable protests it was decided to replace the five arch spans in the river with a steel arch. However, the resulting structure was not nearly as attractive.

The New York City Water Department transferred the bridge to the park system in 1955. The bridge was closed to pedestrians in 1960 after several incidents of vandalism on the bridge.

A 2006 study found no major structural problems on the bridge but said it would cost $30 million to reopen the walkway. So far, $5 million in funds has been raised.
As usual, much more information is available from NYC Roads.
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Thursday, July 30, 2009

New York City's Bridges: High, Alexander Hamilton, and Washington Bridges

After crossing under eight movable bridges, we reach the northern part of Manhattan where three arch bridges span high above the Harlem River. This is in the Washington Heights area, a ridge that rises to 265 ft above sea level (where Fort Washington stood during the American Revolutionary War).

The first (southernmost) structure is the High Bridge, which has been closed for many years. However, Mayor Bloomberg promised during an Earth Day celebration that he would allocate resources to reopen this pedestrian bridge (and former aqueduct).

The next structure is the Alexander Hamilton Bridge, which is part of the Trans-Manhattan Expressway. This 12-lane expressway carries traffic from the George Washington Bridge over the Hudson River across Manhattan to the Alexander Hamilton Bridge across the Harlem River.

The third (northernmost) structure is the Washington (Heights) Bridge a very old (1888) historic structure that currently carries 181st Street traffic across the Harlem River.

We will look at each of these bridges in more detail over the next few days.
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Wednesday, July 29, 2009

New York City's Bridges: Macombs Dam Bridge

This bridge's name derives from an earlier bridge and dam that Alexander Macomb (a farmer and landowner) built on this site in 1814. The current bridge was designed by Alfred P Boller and it was completed in 1895. The main span is 412 ft long over two 150 ft wide channels. Thus, it is the biggest of Boller's Harlem River swing bridges and it's considered the most attractive of his Gothic Revival designs. Like his other bridges, the Macombs Dam Bridge consists of an oddly-shaped through truss due to the tower above the center pier. It was recently rehabilitated (as shown in photo) with new trusses, a new deck, and a new motor. In fact plans have also begun to retrofit this bridge to resist an earthquake that is likely to occur in the area.

As usual, much more information on this bridge is available from New York City Roads.
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Tuesday, July 28, 2009

New York City's Bridges: 145th Street Bridge

Another Alfred P. Boller swing bridge very much like his Madison Avenue and Macombs Dam Bridges over the Harlem River. The 145th Street Bridge was built between 1901 and 1905 with a 300 ft long swing span. A great deal of information about this bridge is provided online by the City of New York Roads.

On a modern swing bridge, the center span is supported on a piston that is lifted up by hydraulics and then swung around with an arm (there are also locking devices at the ends of the swing span). The machinery that drives these early 20th century swing bridges are similar. As a bridge engineer, I rely on a mechanical engineer to design this machinery, although I suppose there may be some engineers who can design a movable bridge on their own. The operation of these bridges also relies on the Coast Guard who maintain the safety of waterways as well as with municipal authorities who periodically inspect the bridge (and the bridge operator). Thus, a movable bridge is a kind of hybrid which requires close cooperation between many different disciplines.
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Monday, July 27, 2009

New York City's Bridges: Madison Avenue Bridge

I think we're going to get tired of Harlem River swing bridges before we ever reach the Hudson. It's funny that people in Paris can get all their needs met living next to a river crossed by low arch bridges while New Yorkers require a dozen movable bridges across the Harlem River.

The Madison Avenue Bridge was designed by Alfred P. Boller and built in 1910 to replace an earlier swing bridge. It has a Y-shaped ramp on the Manhattan side that carries Madison Avenue and 138th Street traffic to and from the Bronx. The main span is 300 ft long with about 25 ft of clearance over the river. It has four vehicle lanes, two sidewalks, and carries about 50,000 vehicles a day.

Like the other Harlem River swing bridges it has a wide hexagonal fender protecting the center pier. It has gazebos at each corner, one of which has perhaps been enlarged to measure the water level. There is also a building for the operator above the pivot pier. The center span is a truss very similar to the center span of most the swing bridges across the Harlem River.
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Sunday, July 26, 2009

New York City's Bridges: Park Avenue (Metro North) Railroad Bridge

A shipping channel was dug in the 19th century by the US Army Corps of Engineers in the Harlem River and crossed by a succession of fixed and movable bridges. Today, the Harlem River is eight miles long (between the East and Hudson Rivers), it's about 18 ft deep at low tide, and it's about 350 ft wide. Most of the movable bridges cross at a skew, making the main span even longer, and so the piers were built in the river.

The current Park Avenue Bridge is the fourth movable bridge at this site and the first lift bridge. It was built between 1954 and 1956 alongside the older bridge. It carries four railroad tracks and has 25 ft of vertical clearance closed and 135 ft when it's open. The main span is 340 ft long. It was originally owned by the New York, New Haven, and Hartford Railroad and it's currently owned by Metro North.
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Saturday, July 25, 2009

New York City's Bridges: Third Avenue Bridge

Actually, this photo is of the 1898 swing bridge that was replaced in 2004. A new swing bridge was floated into place by a barge to replace the center two spans of the existing bridge.

This part of the Harlem River (between Manhattan and the South Bronx) is crossed by a variety of movable bridges, which make an interesting subset of river crossings. Among the various movable bridges are bascule bridges, like giant teeter-totters. There are swing bridges (like the Third Avenue Bridge) that move the channel spans parallel to the waterway. There are lift bridges (like the Triborough Lift Bridge) that are like elevators that raise the channel spans up to the top of towers. There are several less common movable bridge types, including innovative recent designs for footbridges. Most movable bridges require an operator to safely open and close the bridge, a mechanical engineer to maintain the bridge, and some patience on the part of the public every time a ship wants to pass. Therefore, if a bridge carries many vehicles, engineers will try to build it high enough so it doesn't interfere with river traffic. However, this requires long ramps to raise the deck above the tallest vessel. Since the latest Maersk container ships can be 80 meters above the water, that makes keeping bridges out of their way quite a challenge.
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Friday, July 24, 2009

New York City's Bridges: Willis Avenue Bridge

I'm afraid the next few bridges upstream on the Harlem River are being replaced.

The Willis Avenue Bridge is an interestingly-shaped swing bridge that was built in 1901. It carries traffic from First Avenue in Manhattan to Willis Avenue in the Bronx. Apparently it's getting old and it's also a source of accidents and so the City of New York wanted to replace it. They offered to sell the existing bridge for $1 and even promised to move it for the buyer, but there were no takers. The estimate for the replacement bridge was $417 million but when the bids were opened, the low bid was $617 million, which will make it the most expensive bridge across the Harlem River.
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Thursday, July 23, 2009

New York City's Bridges: Triborough Lift Bridge


This is the Manhattan arm of the Triborough Bridge. Robert Moses wanted it to cross the Harlem River at 103rd Street (a straight shot across Ward's Island into Queens) but a variety of pressures resulted in it being constructed at 125th Street instead. It was built to resemble the George Washington Suspension Bridge across the Hudson River (on the other side of Manhattan) with its tall, steel-laced towers.

Its a three-span bridge with a 310 ft lift span supported on 210 ft high towers and a 770 ft total length. In the closed position the deck has a 55 ft vertical clearance over the Harlem River and in the open position it is 135 ft above the river. The bridge carries six lanes of traffic and two sidewalks. It was originally going to be the world's heaviest lift bridge, but the designer, Othmar Ammann was able to reduce its weight by such means as replacing the concrete deck with asphalt on a steel deck. The Triborough Bridges were opened to traffic in 1936.
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Wednesday, July 22, 2009

New York City's Bridges: Ward's Island Bridge

The Harlem River flows along the east side of Manhattan, north of Ward's Island. At the river's mouth is Ward's Island Bridge (sometimes referred to as the Harlem River Pedestrian Bridge), the only footbridge across the Harlem River. This rather spindly-looking structure was designed by Othmar Ammann in 1939, but because steel wasn't available until after the war, construction didn't begin until 1949.

It's a lift bridge with counterweights to raise the 330 ft long center span to the top of the towers. In fact, the bridge is only used from April to October and the center span is left in the raised position for the rest of the year.
The bridge consists of four ramps carrying pedestrians across FDR Drive on the Manhattan side, three spans across the Harlem River, and a gradual descent onto Ward's Island.

It has a modern, streamlined appearance, but because it is 937 ft long with tall towers and only 12 ft wide, it lacks a dramatic presence and appears flimsy.
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Tuesday, July 21, 2009

New York City's Bridges: Triborough and Hell Gate Bridges (2)

Both the Triborough and the Hell Gate Bridges have architectural details without structural purpose.
The Triborough Suspension Bridge has vertical members between the tower struts and finials at the top of the tower legs that make the bridge resemble a piece of Arts-and-Crafts furniture.

The arch on the Hell Gate Bridge has a reverse curve at the ends to give it a more interesting shape without improving its strength. Moreover, the stone towers at the ends of the arch serve no purpose.
Engineers often feel obliged to dress up their bridges in architectural details that do little or may even detract from their structural form. This is discussed in detail in 'The Tower and the Bridge," by David P. Billington.
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Monday, July 20, 2009

New York City's Bridges: Triborough and Hell Gate Bridges

North of Roosevelt Island, two handsome bridges connect Ward's Island to the Queens across the East River.
The Triborough Suspension Bridge has a 1380 ft long main span. It was designed by Othmar Ammann and completed in 1936. It is part of the 'Y' shaped Triborough Bridge Project which includes a lift bridge over the Harlem River and a truss bridge over the Bronx Kill, a narrow strait separating Randall's Island from the Bronx. This project was originally owned by the City of New York, but it was transfered to the Triborough Bridge and Tunnel Authority in 1933.
North of the Triborough Suspension Bridge is the Hell Gate Arch Bridge, a railroad bridge with a 1017 ft main span. It was designed by Gustav Linderthal and completed in 1917.
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Sunday, July 19, 2009

New York City's Bridges: Queensboro Bridge (2)

A closer look at the Queensboro Bridge on Roosevelt Island. It is a five span truss bridge with long approaches. The center span (over Roosevelt Island) is 630 ft long. The west cantilever span (to Manhattan) is 1182 ft long. The east span (to Queens) is 984 ft long. The side spans are 469 and 459 ft long. The entire bridge including the approaches is 7449 ft long. It is supported on four, 350 ft tall steel towers on stone piers (a tower for the Roosevelt Island Tramway can be seen next to the bridge tower in the photo).

The Queensboro Bridge carries an 80-ft wide double deck roadway, which at one time carried trolleys and trains, but now carries nine traffic lanes and a bicycle path and walkway. It carries about 200,000 vehicles a day but several of the lanes are restricted to automobile traffic. The trolley on the bridge used to stop at Roosevelt Island, but now residents can take the tramway or a subway between Manhattan and Roosevelt Islands.

Maintenance of the bridge was neglected for many years. In the early 1980's a $300 million project was begun to repair the bridge, which was completed on the bridge's centennial. Because of the expense of maintaining this bridge, Mayor Bloomberg tried to transfer ownership to the MTA so that tolls could be collected, but that idea was stopped by Governor Pataki.

The other East River crossings (south of the Queensboro Bridge) were suspension bridges with 1470 ft to 1600 ft main spans. Because Roosevelt Island reduced the span length to the channel width on each side of the island, a cantilever truss bridge with shorter spans could be built. Linderthal (the chief engineer on the project) hired an architect and tried to make the bridge as attractive as possible. It was considered by many to be the height of elegance after it was built. It also greatly expanded the development of Queens. More information on the bridge can be found on a website maintained by Steve Andersen about New York City Roads.
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Saturday, July 18, 2009

New York City's Bridges: Queensboro Bridge

There are no crossings over the East River for the three miles north of the Williamsburg Bridge until we reach the Queensboro Bridge at Roosevelt Island.

This interesting structure was designed by Gustav Linderthal (Commissioner of Bridges for the City of New York) and completed in 1909. It is a double cantilever truss bridge without drop-in spans. The cantilever arms come together at mid-span over the channels on each side of Roosevelt Island.

This bridge had a variety of problems during its construction. A windstorm damaged a span, labor unrest caused delays, and the collapse in 1907 of another cantilever truss structure, the Quebec Bridge stopped construction until the dead and live loads could be reduced on this structure.

Although it is now thought to be a handsome structure, after it was built the bridge's architect, Henry Hornbostel complained, "My God - it's a blacksmith's shop." This complaint that steel bridges are less attractive was common at the beginning of the 20th century and led many cities to prefer reinforced concrete bridges for their river crossings.
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Friday, July 17, 2009

New York City's Bridges: Williamsburg Bridge

Continuing north, the next suspension bridge to cross the East River is the Williamsburg Bridge. When it was built in 1903 it had the longest main span in the world of 490 m (and 106 m tall towers). Although big, it's currently dwarfed by the Akashi Kaikyo Bridge with its 1991 m main span and 300 m towers.

Cities like London, Paris, and Tokyo are lucky to have narrow rivers that can be crossed by arch bridges while cities like Shanghai or New York have wide rivers that are more difficult to cross.

Like the nearby Mahattan Bridge, the Williamsburg Bridge carries bikes, pedestrians, trains, and vehicle lanes on two decks. However, it is much more attractive and presents a more unified appearance. The two-legged towers are built up of laced members that match the appearance of the truss superstructure.
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Thursday, July 16, 2009

New York City's Bridges: Manhattan Bridge

A little north of the Brooklyn Bridge is the Manhattan Bridge. It has a main span length of 1470 ft (448 m), which is a little shorter than the Brooklyn Bridge. It was designed and built by Ralph Modjeski and completed on December 31, 1909.

It has an open top deck with two lanes of vehicle traffic on each side and its bottom deck carries a pedestrian lane, a bicycle lane, four sets of subway tracks, and three reversible lanes.
The photo shows the east side of the Manhattan Bridge surrounded by a gentrified area of Brooklyn. The Manhattan Bridge is not nearly as attractive as the Brooklyn Bridge (in my opinion). Perhaps it looks a little kitschy with its squat steel towers painted a metallic blue. It's a favorite of movie directors and has appeared in many films. In Cloverfield the protagonists are trying to get across the Brooklyn Bridge, which is suddenly attacked by a monster while we see the undisturbed Manhattan Bridge in the background.
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Wednesday, July 15, 2009

New York City's Bridges: Brooklyn Bridge (3)

A view from the top deck of the Brooklyn Bridge. A nice thing about this bridge is that you can drive on it, ride on it, run on it, walk on it, or plop on a park bench and sit on it. As can be seen in the photo, the bridge makes for a relaxed and pleasant environment.

Construction of the Brooklyn Bridge was completed on May 24, 1883. It received major repairs after it's 100th anniversary, but it's currently the only New York City owned bridge to get a 'poor' rating. About half a billion dollars in repairs are scheduled over the next few years, which will hopefully bring the bridge back to a 'satisfactory' rating. However, thousands of heavy vehicles every day may be too much for this structure. A restricted load rating may do more than repairs to keep this bridge around for another 126 years.
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Tuesday, July 14, 2009

New York City's Bridges: Brooklyn Bridge (2)

A view of the Brooklyn Bridge from Brooklyn. A nice thing about this view is the Manhattan skyline is behind the bridge.

John Roebling, a German immigrant, was a romantic, a follower of Hegel, and a tough dad. When the Civil War began, he saw his son sitting at the dinner table and demanded to know why he hadn't joined the army.
Colonel Washington Roebling conducted himself well in the war and then returned to help his father.

In those day, workers labored under the caissons, removing the soil to allow the tower foundations to slowly sink to the correct depth. Pressurized air was used to keep the area under the caisson's dry. When workers returned to the surface, the pressurized gas in their blood vessels exploded, injuring and sometimes killing them. Eventually, they learned to rest in the airlock while the air pressure in their bodies slowly returned to normal. This lesson came too late to help Washington, who was incapacitated by caisson disease and spent the next eleven years watching his wife build the bridge from his bedroom window. Despite his illness, he outlived his wife by many years and even remarried.
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Monday, July 13, 2009

New York City's Bridges: Brooklyn Bridge

I still have more photos of Japan's bridges, but I thought we'd take a break to look at some New York City bridges.
Manhattan Island is separated from New York and New Jersey by the Hudson and the East Rivers. The East River is actually a swiftly moving tidal strait carrying water between New York Bay and Long Island Sound.
Traveling north, the first bridge that crosses the East River (between Manhattan and Brooklyn) is one of the world's most famous structures, the Brooklyn Bridge. Even the most cursory description of this bridge would take many pages. If you are interesting in learning more about this bridge, I would recommend reading The Great Bridge by David McCullough (I also enjoyed David's history of John Adams).
John Roebling was able to advance cable and cable bridge technology during an illustrious career in the United States. He successfully convinced politicians of the economics and feasibility of building a bridge across the East River after the Civil War. Unfortunately, he died of an infection after his foot was crushed by a barge at the start of the bridge's construction. His son took over, but he was soon incapacitated by the bends from working on the closed caisson construction. His wife Emily Roebling took over and spent the next eleven years completing the bridge.
However, it was John Roebling's design that makes this bridge such a pleasure to everyone who sees it. The large granite towers with their majestic gothic arches, the wonderful upper deck where runners and bicyclists fight their daily war, the splendid views of the Manhattan skyline, all make traveling under or across the bridge a rewarding experience.
Note that this bridge is a combination suspension/cable-stayed structure with the diagonal stays clearly seen in this photo.

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Sunday, July 12, 2009

Honshu-Shikoku Bridges: Shin-Onomichi Bridges

On the other end of the Nishi-Seto Expressway are the Onomichi and Shin-Onomichi Bridges. They cross the Onomichi-Suido Strait and connect Honshu to Mukaishima Island.

The Onomichi Bridge (on the right) was built in 1968 and was the first modern cable-stayed bridge in Japan. Ownership transfered to the Honshu Shikoku Expressway in 1988.

Because the Onomichi Bridge had only two lanes, the new Shin-Onomichi Bridge was begun in 1993 and completed in 1999. It has two single-legged towers and it was designed not to disturb the aerodynamic stability of the older bridge. Cranes were positioned at the ends of the deck farthest from each tower to lift the steel box girder segments into place.
Both bridges are strange mixtures of reinforced concrete and structural steel. The older bridge is completely steel except for the bottom of the towers. The new bridge has a steel superstructure supported by reinforced concrete towers.
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Saturday, July 11, 2009

Honshu-Shikoku Bridges: Kurushima Bridge (2)

Bridge building can be a dangerous profession. There were 27 deaths building the Brooklyn Bridge including the death of the designer, John Roebling. There were 16 deaths building the Sydney Harbor Bridge.

The Kurushima Bridge was designed so that some of the back spans (spans 6, 7, and 9) were supported on piers rather than from the suspension cables. These spans were incrementally launched from the anchorages onto temporary steel platforms. A week before we visited the bridge, they were dismantling a platform when it suddenly slipped from it's cables, sending seven workers to their death. After the accident, the platform lowering system was replaced using ground-based cranes.

Unfortunately, it sometimes takes an accident before improvements can be made. A safety commission conducted a study of the accident and made recommendations to improve the safety of this widely used incremental deck launching system.

Although bridge construction remains a dangerous profession (about 60 deaths per 100,000 workers) it is eclipsed by pilots (70 deaths per 100,000 workers), fishermen (71 deaths per 100,000 workers), and loggers (118 deaths per 100,000 workers).
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Friday, July 10, 2009

Honshu-Shikoku Bridges: Kurushima Bridge (1)

The rest of the bridges on the Honshu-Shikoku Expressway were in various stages of construction when I went on my tour in 1998.

Like the previously studied Ohmishima and Tatara Bridges, the Kurushima Bridge is part of the Nishi-Seto Expressway. It is the westernmost bridge and connects Shikoku to Oshima Island across Kurushima Strait in the Inland Sea. I say bridge, but its really three suspension bridges with four anchorages and six towers. In total, it's the world's longest suspension bridge at 4015 m (13173 ft). It's similar in construction to the west spans of the San Francisco-Oakland Bay Bridge, which has four towers and a third anchorage in the middle of the bridge.

Because of occasional rough seas and to protect the waters in the Kurushima Strait, several of the towers have energy absorbing devices to protect them and ships that may possibly collide with the towers. This has become a heated issue, especially after single hull oil tankers collide with bridges. Bridge owners are usually blamed for the resulting oil spill, even when the shipping channel under the bridge is wider than 600 m. In any event, the use of energy absorbing devices is suppose to prevent ship damage, although it is likely that a tanker going at 16.5 knots (the speed of the Exxon Valdez) would be seriously damaged by a stationary object, with or without the use of energy absorbing devices.
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Thursday, July 9, 2009

Honshu-Shikoku Bridges: Tatara Bridge (3)

A last look at the Tatara Bridge. The Honshu-Shikoku Bridge Authority kindly took me on a boat trip in 1998 to look at construction of their expressway. The Tatara Bridge was complete except for some final work on the deck. It was a rainy day and clouds had descended to the tops of the towers.

The main span of the Tatara Bridge is a 890 m steel box girder. The side spans are 270 m and 320 m long and are prestressed concrete box girders at their ends to balance the weight. More information on fabrication of the bridge is provided by Uesugi Hideo and information on the erection of the bridge is provided by Satou Yoshyuki.
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Wednesday, July 8, 2009

Honshu-Shikoku Bridges: Tatara Bridge (2)

Private corporations own, maintain, and collect toll revenue on most of the expressways in Japan. The Hanshin Expressway Corporation owns a dozen expressways in the Kansai region including the Wangan Expressway along Osaka Bay. The Honshu-Shikoku Bridge Expressway Company owns three expressways that connect Honshu to Shikoku. This includes the westernmost Nishi-Seto Expressway (National Highway 317). The expressway is 46.6 km long and includes nine long-span bridges that connect seven islands. We looked at the Ohmishima Bridge on the Nishi-Seto-Expressway two days ago. Just north is the Tatara Bridge, which had the longest main span (890 m) of any cable-stayed bridge when it was built in 1999. We also studied this bridge before (on February 8, 2009).

It crosses over the Tatara Strait between Ikuchijima and Ohmishima Islands. It was originally planned to be a suspension bridge, but advances in cable-stayed technology eventually made this bridge a more economical and environmentally friendly alternative. It took nine years, from August 1990 to May 1999, for the Tatara Bridge to be built.
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Tuesday, July 7, 2009

Osaka Bay Bridges: Shorenji-Gawa Bridge

We left Osaka Bay a few days ago but I want to return to look at an interesting bridge.

The Shorenji-Gawa Bridge (north of the Tempozan Bridge) in Osaka is a three span continuous steel girder bridge on the Wangan Expressway.

It's unusual for a steel girder bridge because it's really long, with a 235 m (772 ft) center span. Steel girder bridges with spans greater than 200 m (650 ft) are extremely rare because they are so deep that the dead load becomes a problem. This bridge required a lot of analysis and many tests to ensure that it could resist the wind and buckling.
The bridge superstructure was constructed in three sections, carried to the mouth of the Shorenji River, and lifted onto the piers with two floating cranes.
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