Extradosed bridge
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 , 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 and, and over fifty such bridges had been constructed around the world as of 2012. Whilst incurring many of the construction costs of both the cable-stayed and girder bridge types, extradosed bridges can deliver material savings to offset much of this penalty. They have frequently been adopted when overall height, navigation clearance, or aesthetic requirements have made the cable-stayed or girder alternatives less feasible.
History
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 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. 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 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, wide Ibigawa and Kisogawa "Twinkle" bridges, spanning and 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 long Arrah-Chhapra Bridge in India became the longest bridge of this type.
In 1996, a short 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, 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 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 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 the significant majority of them are located in Japan and South Korea. The longest-span example remains the 2001 Kisogawa Bridge at.
Design characteristics
Visually, extradosed bridges typically have the appearance of a cable-stayed bridge with very short towers, with cable stays of shallow angle that may not extend along the full length of the deck, and with a more substantial deck superstructure. Developed as a hybrid structure between the classic cable-stay and cantilever-girder bridge types, they can offer cost saving and aesthetic opportunities for medium-length bridges in the to span range.Their hybrid nature can lead to significant additional complexity in their design, as the response of the bridge to applied loads is determined by the interactions between:
- the flexural stiffness of the deck/girder superstructure;
- the axial stiffness of the cable stays;
- the height and longitudinal stiffness of the towers/pylons;
- the lengths of adjacent spans and back-spans;
- the degree of fixity between the superstructure, the towers and the substructure;
- the flexural stiffness of the main support piers.
From a structural perspective, the second extradosal characteristic is the reduced proportion of superstructure live load that is carried by the cables. On cable-stayed bridges, the stays commonly support at least 80% of the loading from vehicular traffic acting on the bridge superstructure, whereas on extradosed bridges, the stay cables typically support only between 20% and 60% of this load. In both cases, the remainder of the load is carried by the longitudinal girder element in spanning-action between the main bridge supports. This characteristic derives from the relative stiffnesses between the cable stays and the girder element. Cable-stay designs typically incorporate flexible deck structures without a stiff girder element, and such systems transfer the majority of any applied deck loads directly into the nearest stay cables. In comparison, extradosal designs utilise a substantially stiffer deck/girder structure, allowing the girder to support a significant proportion of any deck loads, and facilitating the distribution of the remaining load between a larger number of individual stay elements.
onstant dead load, its live load can be highly variable both in time and position, resulting in fluctuations in the stress level experienced by the bridge's structural elements as the live loading varies. The lower proportion of live load carried by the extradosed cables results in a reduced magnitude of stress fluctuations within the cables, down from typically or above for cable-stay bridges to around for extradosed designs. This has a direct benefit in reducing the detrimental effects of fatigue experienced by the stay cables and their end anchorages, and bridge design codes allow extradosed stay cables to operate at a significantly higher design stress level and therefore material efficiency level as a result.
As a result of these characteristics, the "stay cables" on extradosed bridges are not treated as such by the design codes, but are instead considered as external post-tensioning tendons that have been deviated upwards from the deck to the towers to increase the superstructure's load capacity over the main supports. Extradosed bridges frequently extend this approach by making the extradosed tendons continuous over the towers via saddle supports and using anchorages only at the deck connections, significantly simplifying the tensioning operations.
By country
Bolivia
The Triplets are the first three extradosed concrete bridges in Bolivia. The construction of a beltway allowing traffic decongestion in the city of La Paz was completed in 2010. The new elevated road crosses three parallel valleys with signature bridges. These three consecutive bridges have similar features and as a result are called the Triplets. All three-span structures are made of concrete, with maximum span of 372 feet, featuring extradosed pre-stressed concrete. The structures are built using balanced cantilever segmental construction. The elevation of the bridges reaches heights between 130 and 197 ft above the bottom of the valley, which made a cable-stayed bridge option, with pylons higher than 82 ft above the deck, inappropriate for the site. Therefore, it was proposed an extradosed bridge type, which reduces the height of the pylon, and a single plane of stays to allow a more transparent view. The bridges were designed by PEDELTA.Canada
The North Arm Bridge is a transit-only bridge of SkyTrain Canada Line, connecting Vancouver with its suburb of Richmond crossing over the Fraser River. The bridge went into service on August 17, 2009, coinciding with the opening of the Canada Line.The Golden Ears Bridge, crosses the Fraser River between the municipalities of Pitt Meadows / Maple Ridge and Langley. It is the longest extradosed bridge in North America. The bridge opened to traffic on June 16, 2009.
India
India's first extradosed bridge, Nivedita Setu, was completed 2007 by Larsen & Toubro Ltd. for the Second Vivekananda Bridge Toll corporation over river Hooghly, Kolkata. This bridge is long, with a span of.The 3rd Narmada Bridge, which bears a similarity to the Golden Ears Bridge in Vancouver, Canada, was completed March 2017 across Narmada river in Bharuch, Gujarat. It is the first extradosed bridge to be built in state of Gujarat and its span of is the longest in India.
A few months later in June 2017, the Arrah–Chhapra Bridge opened across the Ganges river connecting Arrah and Chhapra in Bhojpur and Saran districts in the state of Bihar. It is the longest multi-span extradosed bridge in the world, with a main bridge length of.
Ireland
Ireland's first extradosed bridge, the Rose Fitzgerald Kennedy Bridge, was built by BAM and Dragados, and opened for traffic in January 2020. It is 894 m long, 21.9 m average width with 9 spans, with a maximum length of span of 230 m that will be the longest span constructed up to now in an extradosed cable-stayed with concrete deck. The bridge spans the River River Barrow south of New Ross and is part of the N25 national primary route. This forum contains many photos and details.Latvia
The Southern Bridge over the Daugava River in Riga, Latvia, is as of 2010 the biggest construction project in Latvia and its capital city, Riga. In work volume it can only be compared to the Island Bridge that was built in the 1970s. Work on the development of the Southern Bridge project started in 2002, when the City Development Department of the Riga City Council developed the design task for the route of the bridge, which would connect Vienības Anenue on the left bank of the Daugava River and the Slāvu Roundabout on the right bank. The Southern Bridge over represents a multispan extradosed structure of 49.5 + 77 + 5 × 110 + 77 + 49.5 metres with six traffic lanes. The total length of the bridge is 803 metres. The width is 34.28 metres. There are six pylons, each at a height 13.33 metres above the roadway pavement. Each pylon has eight pairs of cables.Norway
The first extradosed bridge in Scandinavia is the Harpe Bridge crossing the Norwegian river Gudbrandsdalslågen as part of the highway E6. The bridge was opened for traffic December 17, 2016. It is 324 meters long and carries four lanes of traffic.Pakistan
Pakistan inaugurated its first extradosed bridge for traffic on August 21, 2014. The Earthquake Memorial Bridge was built in four years on the Jhelum River in Muzaffarabad, the capital of Azad Jammu Kashmir region of Pakistan. The bridge is 60 metres above the river and 246 metre long. The cable-stayed extradosed bridge was designed and funded by the Japan International Cooperation Agency at the cost of approximately Rs 1.5 billion. The bridge connects Naluchi and Chattar areas of Muzaffarabad reduced commuting duration by an hour.Poland
The largest extradosed bridge in Europe, one of the largest in the world, was completed in July 2013 and was planned to open to traffic on 26 July over the Vistula River in Kwidzyn, Poland. The total length of the bridge is with the main span of 204 m. The bridge has been commissioned by General Directorate for National Roads and Highways, designed by Transprojekt Gdanski and is built by Budimex and Ferrovial Agroman at a cost of 90 million EUR. In addition to the bridge, three more flyovers with total length of 1028.4 m and two bridges over the rivers Młyńska Struga and Liwa will be formed.Parts of bridge:
- The bridge over the Vistula River in length
- El part
- E2 part
- E3 part
above objects are construction of prestressed concrete box-
- three-span bridge over the river Liwa length 51 m - span 15.7 + 19.6 + 15.7 m
- 3 passes for animals spans the 14.3 m;
- 1-local traffic viaduct - span of 30 m;
The bridge was opened on July 26, 2013.
The widest extradosed bridge in the world is Most autostradowy w Mszanie on A1 autostrada.
Sri Lanka
's Road Development Authority is planning to construct an extra-dosed bridge over Kelani River as part of a project aimed at improving traffic condition around existing New Kelani Bridge. The construction will begin in 2017.Tanzania
New Selander Bridge is the first extradosed bridge in United Republic of Tanzania. The 6.23-kilometre New Selander Bridge will attempt to relieve the traffic bottleneck by connecting the area near Coco Beach and Agakan Hospital in Dar es Salaam with a four-lane bridge on the sea. Construction is scheduled to start in the latter half of the year for completion in 2021. From the total length of 6.23 km, the length of the new bridge is 1.03 km. The main bridge itself is 670m long and is designed as an extradosed bridge with a maximum span of 125m. The road consists of a 4.52 km section where two lanes has been expanded to four lanes and a new 0.68 km section.Thailand
is the first extradosed bridge in Thailand. The 4.3-kilometer Maha Chesadabodindranusorn Bridge links the western side with the eastern part of the Nonthaburi province and a new road connecting with Ratchaphruek Road.Turkey
Çallı Bridge, in Antalya city center, is the first extradosed bridge designed and constructed in Turkey. The long bridge has an main span with side spans sustained by 2 x 4 sets of 4 extradosed cables supported above the wide deck by two pylons canted away from the main span. The 6-lane bridge was opened to traffic for Expo 2016.United States
The first extradosed bridge in the U.S. is the northbound span of the Pearl Harbor Memorial Bridge that carries Interstate 95 over the Quinnipiac River in New Haven, Connecticut, which opened to traffic on June 22, 2012. The southbound span opened on August 19, 2015, making it the fourth extradosed bridge in the U.S.The second and third extradosed bridges in the U.S. are Interstate 35 frontage road spans over the Brazos River in Waco, Texas. Construction began in July 2012 and the bridges were dedicated in July 2014. They are the first extradosed bridges to be constructed in Texas.
The fifth extradosed bridge in the United States is the St. Croix Crossing, which crosses the St. Croix River between Oak Park Heights, Minnesota and St. Joseph, Wisconsin. Construction began on the bridge in 2014 and it was opened to traffic on August 2, 2017. The bridge replaced the older Stillwater Bridge in downtown Stillwater, Minnesota, which was functionally obsolete and deteriorating from its age.