Pontoon bridge
A pontoon bridge, also known as a floating bridge, is a bridge that uses floats or shallow-draft boats to support a continuous deck for pedestrian and vehicle travel. The buoyancy of the supports limits the maximum load that they can carry.
Most pontoon bridges are temporary and used in wartime and civil emergencies. There are permanent pontoon bridges in civilian use that can carry highway traffic; generally, the relatively high potential for collapse and sinking and high continuous maintenance costs makes pontoons unattractive for most civilian construction. Permanent floating bridges are useful for sheltered water crossings if it is not considered economically feasible to suspend a bridge from anchored piers. Such bridges can require a section that is elevated or can be raised or removed to allow waterborne traffic to pass. Notable permanent pontoon bridges include the Evergreen Point Floating Bridge, Hood Canal Bridge, and the Nordhordland Bridge.
Pontoon bridges have been in use since ancient times and have been used to great advantage in many battles throughout history, such as the Battle of Garigliano, the Battle of Oudenarde, the crossing of the Rhine during World War II, the Yom Kippur War, Operation Badr, the Iran–Iraq War's Operation Dawn 8, and most recently in the Russian invasion of Ukraine.
Definition
A pontoon bridge is a collection of specialized, shallow draft boats or floats, connected together to cross a river or canal, with a track or deck attached on top. The water buoyancy supports the boats, limiting the maximum load to the total and point buoyancy of the pontoons or boats. The supporting boats or floats can be open or closed, temporary or permanent in installation, and made of rubber, metal, wood, or concrete. The decking may be temporary or permanent, and constructed out of wood, modular metal, or asphalt or concrete over a metal frame.Etymology
The spelling "ponton" in English dates from at least 1870. The use continued in references found in U.S. patents during the 1890s. It continued to be spelled in that fashion through World War II, when temporary floating bridges were used extensively throughout the European theatre. U.S. combat engineers commonly pronounced the word "ponton" rather than "pontoon" and U.S. military manuals spelled it using a single 'o'. The U.S. military differentiated between the bridge itself and the floats used to provide buoyancy. The original word was derived from Old French ponton, from Latin ponto, from pons.Design
When designing a pontoon bridge, the civil engineer must take into consideration Archimedes' principle: Each pontoon can support a load equal to the mass of the water that it displaces. This load includes the mass of the bridge and the pontoon itself. If the maximum load of a bridge section is exceeded, one or more pontoons become submerged. Flexible connections have to allow for one section of the bridge to be weighted down more heavily than the other parts. The roadway across the pontoons should be relatively light, so as not to limit the carrying capacity of the pontoons.The connection of the bridge to shore requires the design of approaches that are not too steep, protect the bank from erosion and provide for movements of the bridge during changes of the water level.
Floating bridges were historically constructed using wood. Pontoons were formed by simply lashing several barrels together, by rafts of timbers, or by using boats. Each bridge section consisted of one or more pontoons, which were maneuvered into position and then anchored underwater or on land. The pontoons were linked together using wooden stringers called balks. The balks were covered by a series of cross planks called chesses to form the road surface, and the chesses were secured with side guard rails.
A floating bridge can be built in a series of sections, starting from an anchored point on the shore. Modern pontoon bridges usually use pre-fabricated floating structures.
Most pontoon bridges are designed for temporary use, but bridges across water bodies with a constant water level can remain in place much longer. Hobart Bridge, a long pontoon bridge built 1943 in Hobart, Tasmania was only replaced after 21 years. The fourth Galata Bridge that spans the Golden Horn in Istanbul, Turkey was built in 1912 and operated for 80 years.
Provisional and lightweight pontoon bridges are easily damaged. The bridge can be dislodged or inundated when the load limit of the bridge is exceeded. The bridge can be induced to sway or oscillate in a hazardous manner from the swell, from a storm, a flood or a fast moving load. Ice or floating objects can accumulate on the pontoons, increasing the drag from river current and potentially damaging the bridge. See below for floating pontoon failures and disasters.
Historic uses
Ancient China
In ancient China, the Zhou dynasty Chinese text of the Shi Jing records that King Wen of Zhou was the first to create a pontoon bridge in the 11th century BC. However, the historian Joseph Needham has pointed out that in all likely scenarios, the temporary pontoon bridge was invented during the 9th or 8th century BC in China, as this part was perhaps a later addition to the book. Although earlier temporary pontoon bridges had been made in China, the first secure and permanent ones in China came first during the Qin dynasty. The later Song dynasty Chinese statesman Cao Cheng once wrote of early pontoon bridges in China :During the Eastern Han dynasty, the Chinese created a very large pontoon bridge that spanned the width of the Yellow River. There was also the rebellion of Gongsun Shu in 33 AD, where a large pontoon bridge with fortified posts was constructed across the Yangtze River, eventually broken through with ramming ships by official Han troops under Commander Cen Peng. During the late Eastern Han into the Three Kingdoms period, during the Battle of Chibi in 208 AD, the Prime Minister Cao Cao once linked the majority of his fleet together with iron chains, which proved to be a fatal mistake once he was thwarted with a fire attack by Sun Quan's fleet.
The armies of Emperor Taizu of Song had a large pontoon bridge built across the Yangtze River in 974 in order to secure supply lines during the Song dynasty's conquest of the Southern Tang.
On October 22, 1420, Ghiyasu'd-Din Naqqah, the official diarist of the embassy sent by the Timurid ruler of Persia, Mirza Shahrukh, to the Ming dynasty of China during the reign of the Yongle Emperor, recorded his sight and travel over a large floating pontoon bridge at Lanzhou as he crossed the Yellow River on this day. He wrote that it was:
Greco-Roman era
The Greek writer Herodotus in his Histories, records several pontoon bridges. Emperor Caligula built a bridge at Baiae in 37 AD. For Emperor Darius I The Great of Persia, the Greek Mandrocles of Samos once engineered a pontoon bridge that stretched across the Bosporus, linking Asia to Europe, so that Darius could pursue the fleeing Scythians as well as move his army into position in the Balkans to overwhelm Macedon. Other spectacular pontoon bridges were Xerxes' Pontoon Bridges across the Hellespont by Xerxes I in 480 BC to transport his huge army into Europe:According to John Hale's Lords of the Sea, to celebrate the onset of the Sicilian Expedition, the Athenian general, Nicias, paid builders to engineer an extraordinary pontoon bridge composed of gilded and tapestried ships for a festival that drew Athenians and Ionians across the sea to the sanctuary of Apollo on Delos. On the occasion when Nicias was a sponsor, young Athenians paraded across the boats, singing as they walked, to give the armada a spectacular farewell. File:035 Conrad Cichorius, Die Reliefs der Traianssäule, Tafel XXXV.jpg|thumb|A relief of a Roman bridge of boats by Cichorius
The late Roman writer Vegetius, in his work De Re Militari, wrote:
The emperor Caligula is said to have ridden a horse across a pontoon bridge stretching two miles between Baiae and Puteoli while wearing the armour of Alexander the Great to mock a soothsayer who had claimed he had "no more chance of becoming emperor than of riding a horse across the Bay of Baiae". Caligula's construction of the bridge cost a massive sum of money and added to discontent with his rule.
Middle Ages
During the Middle Ages, pontoons were used alongside regular boats to span rivers during campaigns, or to link communities which lacked resources to build permanent bridges. The Hun army of Attila built a bridge across the Nišava during the siege of Naissus in 442 to bring heavy siege towers within range of the city. Sassanid forces crossed the Euphrates on a quickly built pontoon bridge during the siege of Kallinikos in 542. The Ostrogothic Kingdom constructed a fortified bridge across the Tiber during the siege of Rome in 545 to block Byzantine general Belisarius' relief flotillas to the city. The Avar Khaganate forced Syriac-Roman engineers to construct two pontoon bridges across the Sava during the siege of Sirmium in 580 to completely surround the city with their troops and siege works.Emperor Heraclius crossed the Bosporus on horseback on a large pontoon bridge in 638. The army of the Umayyad Caliphate built a pontoon bridge over the Bosporus in 717 during the siege of Constantinople. The Carolingian army of Charlemagne constructed a portable pontoon bridge of anchored boats bound together and used it to cross the Danube during campaigns against the Avar Khaganate in the 790s. Charlemagne's army built two fortified pontoon bridges across the Elbe in 789 during a campaign against the Slavic Veleti. The German army of Otto the Great employed three pontoon bridges, made from pre-fabricated materials, to rapidly cross the Recknitz river at the Battle on the Raxa in 955 and win decisively against the Slavic Obotrites. Tenth-Century German Ottonian capitularies demanded that royal fiscal estates maintain watertight, river-fordable wagons for purposes of war.
The Danish Army of Cnut the Great completed a pontoon bridge across the Helge River during the Battle of Helgeå in 1026. Crusader forces constructed a pontoon bridge across the Orontes to expedite resupply during the siege of Antioch in December 1097. According to the chronicles, the earliest floating bridge across the Dnieper was built in 1115. It was located near Vyshhorod, Kiev. Bohemian troops under the command of Frederick I, Holy Roman Emperor crossed the Adige in 1157 on a pontoon bridge built in advance by the people of Verona on orders of the German Emperor.
The French Royal Army of King Philip II of France constructed a pontoon bridge across the Seine to seize Les Andelys from the English at the siege of Château Gaillard in 1203. During the Fifth Crusade, the Crusaders built two pontoon bridges across the Nile at the siege of Damietta, including one supported by 38 boats. On 27 May 1234, Crusader troops crossed the river Ochtum in Germany on a pontoon bridge during the fight against the Stedingers. Imperial Mongol troops constructed a pontoon bridge at the Battle of Mohi in 1241 to outflank the Hungarian army. The French army of King Louis IX of France crossed the Charente on multiple pontoon bridges during the Battle of Taillebourg on 21 July 1242. Louis IX had a pontoon bridge built across the Nile to provide unimpeded access to troops and supplies in early March 1250 during the Seventh Crusade.
A Florentine army erected a pontoon bridge across the Arno during the siege of Pisa in 1406. The English army of John Talbot, 1st Earl of Shrewsbury crossed the Oise across a pontoon bridge of portable leather vessels in 1441. Ottoman engineers built a pontoon bridge across the Golden Horn during the siege of Constantinople, using over a thousand barrels. The bridge was strong enough to support carts. The Ottoman Army constructed a pontoon bridge during the siege of Rhodes. Venetian pioneers built a floating bridge across the Adige at the Battle of Calliano.