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When and where was the first time moveable bridge?

When and where was the first time moveable bridge?


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Transportation of goods on rivers have been important throughout history, all the way back to the earliest civilization in Mesopotamia, the Indus valley, Egypt, China and more (this might not be the best source in the world, but this should hardly be a controversial claim).

But these same civilizations were also building bridges across their rivers (If a source is necessary this will have to do).

For this reason, I always assumed that some kind of moveable bridges across rivers (to allow passage without impeding ship traffic) must have been very common, even in ancient civilizations such as -- to name only a few -- Egypt, Mesopotamia, Achaemenid Persia and at the very least Rome and Han or Tang-china -- and perhaps even medieval Europe; I acknowledge that such mechanisms would need maintenance and crew to operate them, and a great deal of technical skill to build, but in this regard the ancient civilizations such as Rome or Han China don't seem to have been lacking.
To my own great surprise, I have not been able to online find any examples of moveable bridges (meant to allow ships to pass under, thus excluding medieval drawbridges, whose use was purely defensive) older than the Old London bridge and this source does not specify directly that this was the first moveable bridge ever

My question is, therefore, when and where is the first time moveable bridges appear in history.

Edit: after a little more searching I did come across the 1174 Gaungji Bridge, which one source I found (whose reliability I strongly doubt, as it is a tourist website, for which reason I do not consider my question answered satisfyingly) claim to be the first movable bridge in the world.


The most likely early example of a movable bridge (assuming you allow pontoon bridges) allowing a ship to pass either under or through is Xerxes' pontoon bridge from 480 BC and is cited by Herodotus. Between this and the old London bridge completed in 1209, there is little that one can confidently say qualifies.


With Xerxes' Pontoon Bridges (480 BC) the bridge builders left (Hdt. 7.36.2)

a narrow opening to sail through in the line of fifty-oared ships and triremes, that so whoever wanted to could sail by small craft to the Pontus or out of it. After doing this, they stretched the cables from the land, twisting them taut with wooden windlasses; they did not as before keep the two kinds apart, but assigned for each bridge two cables of flax and four of papyrus.

Unfortunately, Herodotus doesn't provide much detail on this. There were, apparently, three openings but how they were 'constructed' is unclear.

This 2005 University of South Africa master's thesis, From the Scamander to Syracuse: Studies in Ancient Logistics (pdf), proposes that ships passed under the bridge thus:

All types of sailing ships of the time had masts which could be easily unstepped. A passing cargo ship would have needed headroom of two metres at the most with its mast unstepped in order to pass under the bridge cables. With that in mind, it is suggested that the simplest solution to the problem would have been for four triremes on each side of each “gap”, that is, 24 altogether, to have been modified by fitting baulks about twenty metres long lengthwise, raised by 25, 50, and 75 centimetres and one metre successively above the deck level, to lift the road over the cables by a gentle slope to about 2 metres above water level which would have been sufficient for a merchant ship to pass underneath.

On the other hand, Otis Ellis Hovey's Movable Bridges (1926) states that parts of the pontoon could be pulled aside to allow ships through:

at three places boats were lashed together and arranged so that they could be swung aside to allow ships to pass through the openings. These appear to have been genuine pontoon draw spans.

With the Romans favouring fixed arch bridges and with evidence from China inconclusive, Hovey then adds

… it is difficult to trace the use of movable structures for several centuries after the beginning of the Christian era.

This brings us to Old London Bridge (cited by the OP and also by Dijkgraaf in a comment). Started by Henry II in 1176 and completed in 1209 during the reign of his youngest son John, it survived 600 years; a

particular feature of Old London Bridge was the drawbridge which was sited near the middle of the bridge.

"Detail from a 1632 oil painting, View of London Bridge, by Claude de Jongh." Note the movable (drawbridge) centre section. Source: Londonist

This allowed tall ships to pass through and the bridge was also notable for the houses and shops on it, though it was not unique in this respect. Interestingly,

Old London Bridge reached its pinnacle of fame in the sixteenth and seventeenth centuries. Tourists came from all over Europe to admire what was considered a wonder of the world.

Perhaps the centre drawbridge was partly a reason the bridge being 'a wonder of the world'; there is certainly scant evidence for other bridges across rivers with a movable section for ships to pass through which dated from the high medieval period.


Very borderline cases

Hovey's Movable Bridges has a section on Ancient Movable Bridges. He covers ancient Egypt, but makes no mention of ships being able to pass under and there does not appear to be any evidence that such bridges existed. At most (citing Edward H. Knight),

the Egyptians built no permanent bridges across the Nile, but were familiar with framing trestle work, and with pontoon draw bridges.

For the 6th century BC Chaldean bridge mentioned here, there is no evidence that it was movable; it may have had a removable section to allow ships to pass, but we can't say for certain.

Hovey also cites Herodotus on Queen Nitocris of Babylon's bridge (circa. 460 BC) across the Euphrates which had "movable platforms". The purpose of these, according to Herodotus, was to prevent robbers crossing the bridge at night.

Finally, Wikipedia's Bascule Bridges article says these date back to ancient times but provides no sources, and nor is there any mention of ships passing through or under.


Question:
when and where is the first time moveable bridges appear in history.

Egypt 2nd Millennium BC, and we also know of one in Chaldea in the Middle East in the 6th Century BC. Then such navigable bridges disappeared until the middle ages. They began becoming popular, even common place after the Industrial Revolution with mass produced steel which was stronger and lighter than iron or stone and with the invention of engines capable of moving such structures.

Movable Bridges Types, Design and History
Moveable bridge is a bridge that can change position (and even shape in some cases) to allow for passage of boats below. This type of bridge has a lower cost of building because it has no high piers and long approaches but its use stops the road traffic when the bridge is open for river traffic.

The oldest know movable bridge was built in the 2nd millennium BC in the ancient Egypt. History also knows for one early movable bridge built in Chaldea in the Middle East in 6th century BC. Since then they were almost forgotten until Middle Ages when they again appeared in Europe. Leonardo da Vinci designed and built designed and built bascule bridges in 15th century. He also made designs and built models of swing and a retractable bridges.

Source:

  • History of Bridges

Interstate Bridge

The Interstate Bridge (also Columbia River Interstate Bridge, I-5 Bridge, Portland-Vancouver Interstate Bridge, Vancouver-Portland Bridge) is a pair of nearly identical steel vertical-lift, "Parker type" through-truss bridges that carry Interstate 5 traffic over the Columbia River between Vancouver, Washington and Portland, Oregon in the United States.

The bridge opened to traffic in 1917 as a single bridge carrying two-way traffic. A second, twin bridge opened in 1958 with each bridge carrying one-way traffic. The original 1917 structure is the northbound bridge. [1] As of 2006, the bridge pair handles around 130,000 vehicles daily. [1] The green structure, which is over 3,500 feet (1,067 m) long, carries traffic over three northbound lanes and three southbound lanes. It was added to the National Register of Historic Places in 1982, as the "Portland–Vancouver Highway Bridge". [3]

Since 2005, proposals for replacing the bridge have been produced and debated. The bridge is considered responsible for traffic congestion of road vehicles and river traffic. Plans for a replacement bridge, known as the Columbia River Crossing (CRC) project, estimated to cost at least $3.4 billion, had come together by 2012 after many delays, but were very controversial, with both strong support and strong opposition. [7] In late June 2013, the CRC project was canceled, after the Washington state legislature declined to authorize funding for the project. [7]

The Interstate Bridge's name is a simple descriptive one based on its location, as a bridge connecting two states. [1] In 1917, the new bridge gave its name to a Portland arterial street. Shortly before the bridge opened, a pair of streets through North Portland that were planned to be treated as the main route to and from the bridge, Maryland Avenue and Patton Avenue, were renamed Interstate Avenue. [8]


George Washington Bridge is dedicated

On October 24, 1931, eight months ahead of schedule, New York governor Franklin D. Roosevelt dedicates the George Washington Bridge over the Hudson River. The 4,760-foot–long suspension bridge, the longest in the world at the time, connected Fort Lee, New Jersey with Washington Heights in New York City. “This will be a highly successful enterprise,” FDR told the assembled crowd at the ceremony. “The great prosperity of the Holland Tunnel and the financial success of other bridges recently opened in this region have proven that not even the hardest times can lessen the tremendous volume of trade and traffic in the greatest of port districts.”

Workers built the six-lane George Washington Bridge in sections. They carried the pieces to the construction site by rail, then hauled them into the river by boat, then hoisted them into place by crane. Though the bridge was gigantic, engineer Othmar Amman had found a way to make it look light and airy: in place of vertical trusses, he used horizontal plate girders in the roadway to keep the bridge steady. Amman used such strong steel that these plate girders could be relatively thin and as a result, the bridge deck was only 12 feet deep. From a distance, it looked as flimsy as a magic carpet. Meanwhile, thanks to Amman’s sophisticated suspension system, that magic carpet seemed to be floating: The bridge hung from cables made of steel wires�,000 miles and 28,100 tons of steel wires, to be exact—that were much more delicate-looking than anything anyone had ever seen.


Historical Development of Bridges

A bridge is a structure which is built over some physical obstacles such as a body of water, valley, or road, and its purpose is to provide crossing over that obstacle. It is built to be strong enough to safely support its own weight as well as the weight of anything that should pass over it. Bridges were and can be built out of different materials and in different designs, depending on its intended function, terrain where the bridge is built, the material used to make it, and the available funds.

The first bridges appeared in nature by themselves. A log could fall across a stream and form a natural bridge or stones could fall into a river from a nearby cliff. When humans started building bridges, they built them in simple form out of cut wooden logs or planks, stones, with a simple support and crossbeam arrangement, sometimes with use of natural fibers woven together to hold materials. One of the oldest arch bridges in existence is Arkadiko Bridge in the Peloponnese, Greece. It dates from 13th century BC.

Ancient Romans were the greatest bridge builders of ancient times. They built arch bridges and aqueducts some of which still stand today. They also used cement which consisted of water, lime, sand, and volcanic rock. Some of their most beautiful bridges were built over ravines while others were built over rivers where no rock or island emerges from the water to carry the piers.

Indians also built bridges, which is documented in their ancient text the Arthashastra which was written between 4th and 3rd century BC. They used plaited bamboo and iron chain as materials.

The Chinese oldest surviving stone bridge is the Zhaozhou Bridge. It was built from 595 to 605 AD during the Sui Dynasty. It is also it the world's oldest stone segmental arch bridge built with open spandrels.

Between 12th and 16th century many bridges were built with houses on them. They were solution for limited accommodation in walled cities and only France had as many as 35.

Inca civilization used rope bridges, a simple type of suspension bridge, in the 16th century. Hans Ulrich, Johannes Grubenmann, and others improved bridge-building in the 18th century. At the same time Hubert Gautier wrote a book on bridge engineering.

The Iron Bridge, built in Coalbrookdale, England in 1779, was one of the engineering marvels of the time because it used cast iron for the first time.

Industrial Revolution in the 19th century brings truss systems of wrought iron (an iron alloy with a very low carbon) but it did not have the tensile strength to carry the large weights. Enters steel, with its higher tensile strength, which replaces the iron and allows for much larger bridges. Gustave Eiffel, with his fresh ideas, was one of the first to use it.

The first welded road bridge in the world was built by welding pioneer Stefan Bryła in 1927.

With Industrial Revolution many different types of bridge appear and became possible because of technological advancements.


Chicago’s movable bridges

Chicago is not just home to many of the world’s earliest skyscrapers—it’s also a city of bridges. How and why did Chicago become home to so many movable bridges?

by Nikki Snodgrass and Jessica Cilella

Every day, Chicagoans head downtown, traveling to and from work, shopping, dining and generally navigating the area. The stunning architecture and skyscrapers give us plenty of reasons to look up, but next time you cross the river along Michigan Avenue, State Street, Wells Street or Wabash Avenue, look down. You&rsquore walking on one of five different types of movable bridges found in Chicago. There&rsquos a total of 37 movable bridges within the city limits.

Early Bridges

The earliest movable bridge in Chicago was a drawbridge at Dearborn Street built in 1834. Constructed of timber, it was similar to bridges found over moats at medieval castles, with large chains lifting it. In the years that followed, there was much trial and error as new styles were designed. A flood in 1849 swept away a number of floating bridges and drawbridges proved to be too narrow to accommodate the influx of people traveling through the rapidly growing city.

The first swing bridge completed in 1856 at Rush Street was an improvement, but the narrowness was still an issue. Swing bridges were set up like a spinner in a board game, which resulted in ships crashing into them, and vehicle collisions on them were common. In 1863, the Rush Street bridge actually collapsed under the weight of a herd of cattle being driven over it, further proving that the bridges were unstable and impractical. One of the few remaining swing bridges can be found east of Cicero Avenue across the Chicago Sanitary and Ship Canal.

A jackknife bridge was introduced in the early 1890s, but the style was not embraced by the city. Two other styles, the vertical lift bridge and the Scherzer rolling lift bridge, were developed in the mid-1890s. Both can still be found in the city. A vertical lift bridge is pulled up and down from counterweights in two tall towers on either side of it. The Scherzer rolling lift bridge is similar to a rocking chair, with large counterweights above the road level to help balance the bridge as it opens and closes.

Ultimately, though, it was the trunnion bascule bridge that became a Chicago staple.

Chicago Style Bascule

The first trunnion bascule bridge in the country opened in 1902 over the north branch of the Chicago River at Cortland Street. Translated from French, &ldquotrunnion&rdquo means &ldquopivot point&rdquo and &ldquobascule&rdquo means &ldquoseesaw.&rdquo Also known as the &ldquoChicago Style,&rdquo the bridge's leaves are suspended on axles (trunnions), with massive concrete counterweights located below the bridge, in the riverbank pit. There are single-leaf bascule bridges, which were constructed where the river was not very wide and often used for trains, and double-leaf bascule bridges, which could be compared to two seesaws across from each other.

What is it that made these bridges so unique to Chicago and so necessary to perfect? In 1830, right around the time of the first movable bridge design, the city&rsquos population was about 4,000. By 1857, when the swing bridge was being introduced, the population had grown to 90,000. Bascule bridges were the most practical for these large and growing numbers of people and remain common today.

Lasting Legacy

After 1910, involvement from the Chicago Plan Commission and architect Edward Bennett improved the bridges&rsquo architectural elements, including bridge houses. These houses represent many major architectural styles, including Art Deco, Beaux-Arts and Modernism.

Some of the bridges that are still utilized in the downtown area are double decker, with vehicle traffic on the bottom level and L trains passing through on the upper level. Last year, two downtown bridges&mdashat Jackson Boulevard and Lake Street&mdashturned 100 years old!

At the beginning and end of each boating season, every downtown bridge is lifted, to allow people to bring their high-masted boats to the lake. This year, the bridge lifts will begin in mid-April. While it is quite a spectacle for some, many find it bothersome as they wait to walk or drive across the river. Those grumbling should take note, however, that the bridges used to lift much more frequently than they do today. In the 19th Century and part of the 20th Century, bridges were lifted or spinned on demand, whenever a boat needed to pass by. Today, they typically only lift on timed schedules.

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U.S.-Soviet spy swap

On February 10, 1962, American spy pilot Francis Gary Powers is released by the Soviets in exchange for Soviet Colonel Rudolf Abel, a senior KGB spy who was caught in the United States five years earlier. The two men were brought to separate sides of the Glienicker Bridge, which connects East and West Berlin across Lake Wannsee. As the spies waited, negotiators talked in the center of the bridge where a white line divided East from West. Finally, Powers and Abel were waved forward and crossed the border into freedom at the same moment𠄸:52 a.m., Berlin time. Just before their transfer, Frederic Pryor𠄺n American student held by East German authorities since August 1961–was released to American authorities at another border checkpoint.

In 1957, Reino Hayhanen, a lieutenant colonel in the KGB, walked into the American embassy in Paris and announced his intention to defect to the West. Hayhanen had proved a poor spy during his five years in the United States and was being recalled to the USSR, where he feared he would be disciplined. In exchange for asylum, he promised CIA agents he could help expose a major Soviet spy network in the United States and identify its director. The CIA turned Hayhanen over to the FBI to investigate the claims.

During the Cold War, Soviet spies worked together in the United States without revealing their names or addresses to each other, a precaution in the event that one was caught or, like Hayhanen, defected. Thus, Hayhanen initially provided the FBI with little useful information. He did, however, remember being taken to a storage room in Brooklyn by his superior, whom he knew as “Mark.” The FBI tracked down the storage room and found it was rented by one Emil R. Goldfus, an artist and photographer who had a studio in Brooklyn Heights.

Emil Goldfus was Rudolf Ivanovich Abel, a brilliant Soviet spy who was fluent in at least five languages and an expert at the technical requirements of espionage. After decorated service as an intelligence operative during World War II, Abel assumed a false identity and entered an East German refugee camp where he successfully applied for the right to immigrate to Canada. In 1948, he slipped across the Canadian border into the United States, where he set about reorganizing the Soviet spy network.

After learning of Hayhanen’s defection, Abel fled to Florida, where he remained underground until June, when he felt it was safe to return to New York. On June 21, 1957, he was arrested in Manhattan’s Latham Hotel. In his studio, FBI investigators found a hollow pencil used for concealing messages, a shaving brush containing microfilm, a code book, and radio transmitting equipment. He was tried in a federal court in Brooklyn and in October was found guilty on three counts of espionage and sentenced to 30 years imprisonment. He was sent to the federal penitentiary in Atlanta, Georgia.

Less than three years later, on May 1, 1960, Francis Gary Powers took off from Peshawar, Pakistan, at the controls of an ultra-sophisticated Lockheed U-2 high-altitude reconnaissance aircraft. Powers, a CIA-employed pilot, was to fly over some 2,000 miles of Soviet territory to Bodo military airfield in Norway, collecting intelligence information en route. Roughly halfway through his journey, he was shot down over Sverdlovsk in the Ural Mountains. Forced to bail out at 15,000 feet, he survived the parachute jump but was promptly arrested by Soviet authorities.

On May 5, Soviet leader Nikita Khrushchev announced that the American spy aircraft had been shot down and two days later revealed that Powers was alive and well and had confessed to being on an intelligence mission for the CIA. On May 7, the United States acknowledged that the U-2 had probably flown over Soviet territory but denied that it had authorized the mission.

On May 16, leaders of the United States, the USSR, Britain, and France met in Paris for a long-awaited summit meeting. The four powers were to discuss tensions in the two Germanys and negotiate new disarmament treaties. However, at the first session, the summit collapsed after President Dwight D. Eisenhower refused to apologize to Khrushchev for the U-2 incident. Khrushchev also canceled an invitation for Eisenhower to visit the USSR.

In August, Powers pleaded guilty to espionage charges in Moscow and was sentenced to 10 years imprisonment–three in prison and seven in a prison colony.

At the end of his 1957 trial, Rudolf Abel escaped the death penalty when his lawyer, James Donovan, convinced the federal judge that Abel might one day be used either as a source of intelligence information or as a hostage to be traded with the Soviets for a captured U.S. agent. In his five years in prison, Abel kept his silence, but the latter prophecy came true in 1962 when he was exchanged for Powers in Berlin. Donovan had played an important role in the negotiations that led to the swap.

Upon returning to the United States, Powers was cleared by the CIA and the Senate of any personal blame for the U-2 incident. In 1970, he published a book, Operation Overflight, about the incident and in 1977 was killed in the crash of a helicopter that he flew as a reporter for a Los Angeles television station.


A bold idea

One of the boldest attempts with a new material was the application of cast iron to bridges (Thomas Tedgold, English engineer and author, 1824)

As industry around the gorge grew, so did the need for a strong and durable bridge to transport goods across the river. In 1773, Thomas Farnolls Pritchard &ndash an architect from Shrewsbury &ndash had a bold idea. Combining engineering expertise and new iron-casting techniques, he proposed the world&rsquos first iron bridge, which would link the parishes of Madley and Benthall over what was one of the busiest rivers in the country.

Pritchard&rsquos designs were approved by Act of Parliament and in 1777 construction began. Overseen by Darby&rsquos grandson Abraham Darby III after Pritchard&rsquos death, it was to be a cast iron single-span bridge of 30 metres, with five main semicircular ribs.

The radical new structure, which formally opened on New Year&rsquos Day 1781, used a total of 378 tons of iron at a cost of around £6,000 &ndash significantly more than the £3,200 first estimated.


Howe Truss Bridge

A howe truss bridge design includes vertical members and diagonals that slope up towards the center. Its diagonals are under compression under balanced loading. It was invented in 1840 by Massachusetts millwright William Howe. Howe truss design proved to be instrumental not only in the development of several notable bridges at the end of an era of fully wooden bridges but also as an inspiration for the creation of other popular designs.


When and where was the first time moveable bridge? - History

"Good progress has been made in the preliminary steps for the construction of the Interstate Highway Bridge over the Columbia River at Portland, Oreg. For carrying out this undertaking bond issues of $1,500,000 on the Oregon side and $500,000 on the Washington side have been provided. The bridge will be divided into four parts -- one over the main channel of the Columbia River, one over the Oregon slough [North Portland Harbor] , one over the Columbia slough [Columbia Slough] , and an embankment over Hayden Island. The main structure will have 12 steel spans and one movable span. The bridge over the Oregon slough will have 12 girder spans, and the bridge over the Columbia slough will have one girder span with steel trestle approaches. The bridge will be designed for highway and interurban railway traffic, and will have a roadway 38 ft. in the clear and one 6 ft. sidewalk. There will be approximately 9,000 tons of structural steel and about 30,000 cu. yds. of concrete in the structure. Waddell & Harrington, Kansas City, MO. are the consulting engineers."

"There was a growing awareness of a definite need for an interstate bridge. The ferry crossing the Columbia River, operated by the Portland Railway Light and Power Company was steadily increasing its business. In 1915 it averaged over 300 vehicles per day and this figure increased by 6 percent the next year. On one summer Sunday over 700 vehicles were ferried across, a crowd which created a long line and prolonged delay." [Freece, D.W., Masters Thesis, 1984, "A history of the street railway systems of Vancouver, Washington, 1889-1926", Portland State University.]

The first Interstate 5 Bridge has a total of 13 Parker-truss style steel spans, with three measuring 275 feet in length and the remaining ten measuring 265 feet in length.

"The bridge over the Columbia River consists of a series of through riveted truss spans with curved top chords three spans 275 ft. long and ten spans 265 ft. long, together with a small deck girder span at the Vancouvr end, making a total length of 3,531 ft. 5 7/8 ins. between end shoes. Provision for navigation on the river is made by a vertical lift span. The central of three 275 ft. spans is arranaged to lift between towers on the other two, so as to afford a channel 250 ft. wide at right angles to the current of the river and 150 ft. high above ordinary high water." [Harrington and Howard, 1918, The Columbia River Interstate Bridge, Final Report.]

On December 30, 1916, the Interstate Bridge was open to foot traffic due to bad weather and ice on the Columbia preventing the ferry from running.

"1000 CROSS BRIDGE / Ice Blocks Ferry and Interstate Span is Used. / Funeral Cortege Passes / Draw Span Is Lowered for Few Hours in Emergency, and Scores Go to or From Vancouver for Novelty, Despite Cold Wind." [Sunday Oregonian, December 31, 1916]

On January 24, 1917, a streetcar made a trial run over the new bridge between Vancouver and Portland. Opening ceremonies were on February 14, 1917, and the bridge opened for the public use on February 15th. Streetcars had regular schedules between Vancouver and Portland, and continued until 1940 when asphalt was poured over the tracks.

Between 1917 and 1929 a toll of 5 cents per car was levied.

The original bridge is today's northbound lanes.

Construction of the second span (today's southbound lanes) began in 1956 and opened in 1958. The new span was given a rise to allow more boats to pass beneath, to cut back on drawbridge openings. When the new span opened the old span closed for refurbishing and it too was given a rise.

A toll once again was put on the bridge in 1960 (20 cents for cars and light trucks) to help pay for the construction of the southbound lanes and the improvement of the northbound lanes. This toll was removed in 1967.

The entire bridge length is 3,550 feet, with a main span length of 531 feet.


Click image to enlarge
Interstate 5 Bridge heading north to Vancouver, Washington. View from Oregon heading north to Washington State. Today's northbound lanes are the original bridge built as a wagon crossing in 1917. Image taken September 24, 2006.

Click image to enlarge
Interstate 5 Bridge crossing the Columbia River. View from Oregon heading north to Washington State. Today's northbound lanes are the original bridge built as a wagon crossing in 1917. Image taken September 24, 2006.

Click image to enlarge
Drawbridge, Interstate 5 Bridge crossing the Columbia River. View from Oregon heading north to Washington State. Today's northbound lanes are the original bridge built as a wagon crossing in 1917. Image taken September 24, 2006.

The Lift .

According to the "Columbian.com" website (2006): " . The bridge's twin lift spans are hoisted by electric motors with a capacity of about 50,000 pounds per span. That is far less than the spans weigh, of course, so the lifting process relies on concrete counterweights weighing 300 tons each. The counterweights hang on cables that run over sheaves, or pulleys, at the top of the north and sound ends of the 190-foot-tall lift spans. Atop the counterweights can be seen stacks of two sizes of concrete blocks, weighing 2,000 pounds and 100 pounds. As the traffic wears away the road surface, the blocks are removed from the counterweights to compensate, thereby keeping the lift span's balance weight within the capability of the lift motors. . "


Click image to enlarge
Bridge lift, Interstate 5 Bridge, Vancouver, Washington. View from Vancouver Landing, located downstream of the bridge. Image taken July 2, 2011.

Effective February 1, 1917, your Commission issued schedule of tolls as follows:


Pont du Gard

Ancient Roman architects created many impressive structures, but one of their most enduring ones was the aqueduct bridge that crosses Gardon River in southern France. As part of the larger Nîmes aqueduct, this 48.8-meter-tall aqueduct bridge with more than 50 arches was instrumental for transporting clear water from springs of Ucetia to the city of Nemausus and its 50 thousand inhabitants. After centuries of use, the lowest tier of the bridge was partially modified to allow transport of people and was augmented by a side bridge with traditional decking in the 18th century. Today, Pont du Gard is regarded as a national treasure of France and one of its most popular tourist destinations.


Watch the video: New DRAWBRIDGE MOD! Heres How To Make It Work (May 2022).