Ship deflector
A ship deflector is a device that is intended to prevent ships, especially ocean-going vessels, from colliding with bridge piers , or at least to mitigate it so that the bridge does not collapse.
prehistory
For centuries, the stone arch bridges and especially the many wooden bridges were brought to collapse almost exclusively by floods, storms and ice drifts. Since the beginning of the industrial revolution , there have been numerous collapses because the material has not yet met the requirements, the new techniques have not yet been mastered or the bridges have been overloaded.
Collisions between ships, which led to the collapse of mostly individual bridge sections, did not occur increasingly until the 1940s, but received little attention as just one of numerous other causes of collapse. The collision of a tanker with the General Rafael Urdaneta Bridge in Lake Maracaibo in Venezuela in 1964 and the collapse of the Tasman Bridge in Hobart , Tasmania , Australia in 1975 caused by an iron ore freighter were accepted as unavoidable accidents.
It was not until 1980, when the Almöbron in Sweden was brought down in quick succession by a 27,890 DWT freighter and a section of the Sunshine Skyway Bridge in Florida by a similarly sized freighter, that discussions began on how such accidents could be prevented.
Classification of protective devices
Various options were considered and sometimes used, which can be grouped as follows:
Main opening without pillars
The main opening of the bridge will be built so large that the pillars are out of reach of the ships. For example, the Almöbron was replaced by the Tjörnbron , whose pylons were placed high on the opposite banks. This assumes that the greater range can still be bridged at a reasonable cost. The same goal was achieved at the George Washington Bridge by pushing the left bank of the Hudson River so far that the eastern pylon is also dry.
Protection island
In rare cases, a natural island can be used as the foundation for the pillar, as is the case with the Forth Bridge . An artificial protection island can be created if there is a sufficiently solid subsurface and the reduced drainage cross-section is not a problem. There are examples of artificial protection islands at the Puente de las Américas via the entrance to the Panama Canal , at the Laviolette Bridge in Trois-Rivières across the Saint Lawrence River or at the Verrazzano-Narrows Bridge via the port entrance of New York City , whose pylons are surrounded by large walls of heaped boulders.
Ship deflector
Caissons or dolphins
At a distance of 50 to 80 m in front of the bridge piers, round sheet piling boxes are often arranged, which are filled with stones and closed with a reinforced concrete cover. They require a good subsurface and not too great a depth of water. They are intended to absorb the energy of an impact primarily through their mass, and secondarily through their deformation. The pylons of the Sunshine Skyway Bridge over Tampa Bay near Saint Petersburg , Florida, which was newly built to replace the collapsed bridge , are not only protected by islands made of heaped boulders, but also by dolphins with a diameter of 20 m. At the main culverts of the Rio-Niterói Bridge , dolphins were installed on both sides of the pillars , which support each other in the event of an impact via cross connections past the pillars.
Protection systems from piles
Protection systems with individual piles or pile groups ( dolphins ) are also used, also in the form of protective walls, which are formed from a large number of piles close to one another or from sheet pile walls. The foundations of the Astoria Bridge over the Columbia River in Oregon , USA, are surrounded by honeycomb sheet pile structures at a distance of 4 to 6 m. They are supposed to absorb the energy of an impact through their deformation. At the Rosario-Victoria Bridge over the Río Paraná in Argentina, large ship deflector structures were erected at a clearance of 17.5 m in front of the pylons and the following seven piers of the ramp bridge on the river side. They consist of several steel pipes up to 60 m long and 2 m thick, which are filled with reinforced concrete and inserted into the ground at a distance of 5 m. The heads of the pillars are articulated to a very rigid reinforced concrete platform.
Floating systems
Floating systems consist of large, mostly triangular floating bodies, which are anchored a long way from the pillars. They can also be used in great water depths and, with appropriate anchoring, even in poor subsoil conditions. They should slow down a lost ship so far that it is no longer a danger. So you should absorb or at least mitigate the energy of the ship impact with small forces over long distances. Their disadvantage is that they can be run over by very large ships. Examples of floating systems can be found at the Puente General Manuel Belgrano (Puente Chaco – Corrientes) and at the Complejo Zárate - Brazo Largo , both across the Río Paraná in Argentina, and at the Francis Scott Key Bridge in Baltimore , Maryland , USA.
Individual evidence
- ↑ See list of bridge collapses
- ↑ a b Options for protecting bridge piers against ship impact . In: Reiner Saul, Siegfried Hopf, Karl Humpf, Armia Patsch, Adelheid Bacher: Innovative protection against ship impact for the Rosario-Victoria bridge over the Parana (Argentina) . Stahlbau, 72nd year 2003, issue 7, p. 469/473
- ↑ The examples given can be clearly seen in Google Earth. The coordinates relate to one of the pillars or the ship deflector.
- ↑ The English word dolphin was synonymous with dalbe , but is now also used in German as a technical term for such caissons.
- ↑ Adelheid Bacher, Reiner Saul, Karl Humpf, Armin Patsch: Nonlinear calculations of composite steel piles on the ship deflector structures of the Rosario – Victoria bridge in Argentina (PDF, 293 kB)