Pontoon bridge; One of the great Military Engineering Trick
A pontoon bridge (or ponton bridge), also known as a floating bridge, 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 they can carry.
Most pontoon bridges are temporary, used in wartime and civil emergencies. Permanent floating bridges are useful for sheltered water-crossings where 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.
Pontoon bridges have been in use since ancient times and have been used to great advantage in many battles throughout history, among them the Battle of Garigliano, the Battle of Oudenarde, the crossing of the Rhine during World War II, and during the Iran–Iraq War Operation Dawn 8.
VIDEO -Russian Army Pontoon Bridge Construction
Pontoon bridges were extensively used by both the armies and civilians throughout the first half of the 20th century and both World Wars. Operation Badr in 1973, which opened the Yom Kippur War between Egypt and Israel, involved the erection of at least 10 pontoon bridges to cross the Suez Canal. In 1995 the 502nd and 38th Engineer Companies of the U.S. Army’s 130th Engineer Brigade, and the 586th Engineer Company from Ft. Benning GA, as part of IFOR assembled a pontoon bridge under adverse weather conditions across the Sava near Županja (between Croatia and Bosnia), with a total length of 2,034 feet (620 m). It was dismantled in 1996.
When designing a pontoon bridge, the civil engineer must take into consideration the 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 (tidal) 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, was only replaced after 21 years.[15] 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 bridge 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 (flotsam) can accumulate on the pontoons, increasing the drag from river current and potentially damaging the bridge. See below for floating pontoon failures and disasters.
