page_title: Extradosed bridge
section_title: History
hierarchical_section_title: Extradosed bridge / History
caption_attribution_description: Deutsch: Ein Teil der Sunnibergbrücke in Klosters-Serneus, Schweiz English: One of the pillars of the Sunniberg-Bridge at Klosters-Serneus in Switzerland
context_page_description: An extradosed bridge employs a structure that combines the main elements of both a prestressed box girder bridge and a cable-stayed bridge. The name comes from the word extrados, the exterior or upper curve of an arch, and refers to how the "stay cables" on an extradosed bridge are not considered as such in the design, but are instead treated as external prestressing tendons deviating upward from the deck. In this concept, they remain part of the main bridge superstructure.
  Compared to a cable-stayed or cantilever-girder bridge of comparable span, an extradosed bridge uses much shorter stay-towers or pylons than the cable-stayed bridge, and a significantly shallower deck/girder structure than used on the girder bridge. This arrangement results in the typical extradosed "look" of a fan of low, shallow-angle stay cables, usually with a pronounced "open window" region extending from the sides of each tower.
  The extradosal bridge form is mostly suited to medium-length spans between 100 m and 250 m, and over fifty such bridges had been constructed around the world as of 2012.
context_section_description: The earliest bridge known to incorporate some of the features of an extradosed design is Bridge in Rzuchów near Leżajsk, constructed in Poland in 1980. Next is the Ganter Bridge, constructed in Switzerland, designed by Christian Menn of Zurich, it preceded by several years the 1988 publication on the design philosophy of such bridges by Jacques Mathivat, who is credited with inventing the extradosed terminology and its design concepts. The Ganter Bridge is a modified prestressed concrete cantilever girder design, where the longitudinal "continuity" tendons are raised significantly above the deck height at the ends of each main span and supported on short towers. These tendons are encased in fin-like blade walls on each side of the towers for protection, a design arrangement now often referred to as a cable-panel bridge.
  Whilst little is known of the origin of Menn's design, Mathivat developed a theoretical basis for such a concept during 1982-1983 while preparing a tender proposal for the Autoroute A64 viaduct across Arret-Darre in France. Mathivat's design replaced the internal tendons normally located in the top of the box girder with "external" tendons running at a shallow angle from the deck surface in one span up over short towers and back to the next span. These he called extradosed tendons, as they connected to the extradose (or upper surface) of the bridge's spanning structure. The shallow angle of these tendons resulted in them transmitting a large compression force component into the bridge deck structure, allowing them to function in a similar manner to conventional "flexural" bridge prestressing. The extradosed tendons were continuous over the towers and were stressed from the deck level, unlike stay cables, which normally terminate at the top of each pylon.
  The first example of a bridge constructed using Mathivat's concepts appears to be the 1993 Ponte dos Socorridos at Camara de Lobos, Portugal, with a main span of 106 m (348 ft). This was quickly followed by the Odawara Blueway Bridge on the Seisho Bypass, Japan, designed by Akio Kasuga and completed in 1994. This bridge has a 122 m (400 ft) main span, a 16.2-m deck width and utilises four 10.7-m tall pylons each supporting two sets of eight exposed extradosal tendons in a modified fan arrangement. These tendons pass over saddles at the top of each pylon, however it is unclear as to whether they form a continuous tendon between the two spans, as the designers' documentation refers to them being anchored outside each saddle to restrain slip. Numerous bridges have subsequently been constructed in Japan to similar designs, the twin, 33 m (108 ft) wide Ibigawa and Kisogawa "Twinkle" bridges, spanning 271.5 m (891 ft) and 275 m (902 ft) across the Ibi and Kiso Rivers respectively, and completed in 2001. Twinkle bridge was the longest extradosed bridge in the world until 2017, when the 1,920 m (6,300 ft) long Arrah-Chhapra Bridge in India became the longest bridge of this type.
  In 1996, a short 54 m (177 ft) span bridge of the extradosal style was constructed to pass the A43 Autoroute across the Maurienne River at Saint-Remy-de-Maurienne, France. This was followed in 1998 by the curved, 140 m (460 ft) multi-span Sunniberg Bridge in Switzerland, also designed by Christian Menn and utilising low, outward-leaning pylons to minimise its visual impact on the surroundings.
  In North America, a small 104 m (341 ft) fin-backed prestressed concrete bridge was built across Barton Creek near Austin, Texas in 1993 to service a private development. This is similar in concept to the original Ganter Bridge, except that the stay cables are encased within triangular blade walls connecting the deck to the towers. The first "true" extradosal design on the continent is the North Arm Bridge at Vancouver, British Columbia, Canada, which spans 180 m (590 ft) and was completed in 2008.
  Since the mid-2000s the style has grown appreciably in popularity with over fifty bridges with extradosal characteristics being recorded as of 2012. They have been constructed in many countries, although 
caption: Sunniberg Bridge, Switzerland
  Main spans 140 m, 1998
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