Network Arch Bridge
Encyclopedia
A Network Arch Bridge is a tied arch bridge
with inclined hangers that cross each other at least twice.
(Czech Republic) was opened to road traffic in 2004 and has a span of 41 metres.
: Only axial compressive and tensile forces.
Bending moments and shear forces are very small in network arches.
The hanger arrangement is the heart of every network arch and constitutes the main difference to tied arches with vertical hangers. It is defined by the number of hangers, hanger inclination and hanger distance. An easy possibility to achieve an efficient structure is the application of the radial hanger arrangement, which was developed by Benjamin Brunn and Frank Schanack in 2003. In the radial hanger arrangement the distances between the upper hanger nodes and the angle between hangers and arch remain constant. In order to avoid too long hangers this angle may be increased towards the bridge ends.
Usually, transverse bending in the deck is bigger than bending in longitudinal direction. Therefore, a concrete deck that spans between the arches is a good solution for
bridges with arch distances that are not too large. The concrete deck has longitudinal prestressing tendons in the arch planes.
Nielsen stands for the engineer Octavius F. Nielsen who applied for a patent on arches with tie and inclined hanger rods in 1926. This bridge type was then built about 60 times,
primarily in Sweden. None of these bridges had crossed hangers.
Lohse stands for the German engineer Hermann Lohse (1815–1893) who developed a tied arch at late 19th century,
whose tie is conversely curved to the arch. The bridge deck is supported by a
third structural element hanging underneath.
Thus, it can be recognised that the name Nielse-Lohse is not correct for tied arches with inclined hanger crossing each other multiple times.
Furthermore, the archetype of the Japanese network arches is the Fehmarnsund Bridge
, Germany, which itself is based on the network arch idea.
The correct name of tied arch bridges with inclined hangers that cross each other at most once is Nielsen bridge. Tied arches with hangers with multiple intersections are network arch bridges.
This strict rule is justified, because it leads to a more efficient structure.
Tied arch bridge
A tied-arch bridge is an arch bridge in which the outward-directed horizontal forces of the arch, or top chord, are borne as tension by the bottom chord , rather than by the ground or the bridge foundations...
with inclined hangers that cross each other at least twice.
Example
The network arch bridge in BechyněBechyne
Bechyně , is a town in the South Bohemian Region of the Czech Republic. It is located on the Lužnice River 20 km southwest of Tábor and has a population of 5,695 ....
(Czech Republic) was opened to road traffic in 2004 and has a span of 41 metres.
Structure
The inclined hangers with multiple intersections make the network arch bridge act like a trussTruss
In architecture and structural engineering, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in...
: Only axial compressive and tensile forces.
Bending moments and shear forces are very small in network arches.
The hanger arrangement is the heart of every network arch and constitutes the main difference to tied arches with vertical hangers. It is defined by the number of hangers, hanger inclination and hanger distance. An easy possibility to achieve an efficient structure is the application of the radial hanger arrangement, which was developed by Benjamin Brunn and Frank Schanack in 2003. In the radial hanger arrangement the distances between the upper hanger nodes and the angle between hangers and arch remain constant. In order to avoid too long hangers this angle may be increased towards the bridge ends.
History
The network arch idea was developed by the Norwegian engineer Per Tveit in the end of the 1950s.Advantages
Because arch and tie are mainly subject to axial forces, their cross sections can be very small.Usually, transverse bending in the deck is bigger than bending in longitudinal direction. Therefore, a concrete deck that spans between the arches is a good solution for
bridges with arch distances that are not too large. The concrete deck has longitudinal prestressing tendons in the arch planes.
Difference to Nielsen-Lohse-Bridges
In Japan, tied arch bridges with crossing hangers are wrongly called Nielsen-Lohse bridge.Nielsen stands for the engineer Octavius F. Nielsen who applied for a patent on arches with tie and inclined hanger rods in 1926. This bridge type was then built about 60 times,
primarily in Sweden. None of these bridges had crossed hangers.
Lohse stands for the German engineer Hermann Lohse (1815–1893) who developed a tied arch at late 19th century,
whose tie is conversely curved to the arch. The bridge deck is supported by a
third structural element hanging underneath.
Thus, it can be recognised that the name Nielse-Lohse is not correct for tied arches with inclined hanger crossing each other multiple times.
Furthermore, the archetype of the Japanese network arches is the Fehmarnsund Bridge
Fehmarn Sound bridge
The Fehmarn Sound Bridge connects the German island of Fehmarn in the Baltic Sea with the German mainland near Großenbrode.-Description:The long road and rail suspended deck arch bridge together with associated earthworks crosses the wide Fehmarn Sound. Construction began in 1958 and the bridge...
, Germany, which itself is based on the network arch idea.
The correct name of tied arch bridges with inclined hangers that cross each other at most once is Nielsen bridge. Tied arches with hangers with multiple intersections are network arch bridges.
This strict rule is justified, because it leads to a more efficient structure.
More examples
- Bolstadstraumen Bridge, Norway (1963)
- Fehmarnsund Bridge, Germany (1963)
- The replacement for the Lake Champlain Bridge USA, will be a modified network tied arch. The bridge opened in November 7, 2011.
- Providence River Bridge, USA (2008)
- Steinkjer Bridge, Norway (1963)
- Blennerhassett Island BridgeBlennerhassett Island BridgeBlennerhassett Island Bridge opened to traffic June 13, 2008. The bridge is a Network Arch Bridge constructed at a cost of $120 million over the Ohio River between Belpre, Ohio and Parkersburg, West Virginia. Construction of the bridge was completed by the Walsh Construction Company of Chicago.The...
, USA (2008) - John Greenleaf Whittier Memorial Bridge, USA (2015) Under Design by MassDOT expected to open in 2016. Construction starts 2013.
External links
- http://www.network-arch.com (Information on network arch bridges)
- http://home.uia.no/pert/ (Information on network arch bridges by Per Tveit)
- http://www.pineapplestudios.com/IWAYSite (Information on the construction of Providence River Bridge)