Network arch bridge

A network arch bridge is a tied arch bridge with several times crossing hangers. By arranging a hanger network, the bending moments and shear forces are reduced in arc and track support, so that they can be made very thin and up to 20 % compared to a conventional steel tied arch bridge can be saved. There are often network arches two arches and a clamped therebetween deck slab of concrete.

History

The idea of ​​the network arch bridge designed by the Norwegian engineer Per Tveit at the end of the 1950s. The first network bridge was built in 1963-1964 in Steinkjer, Norway, and is still used today.

Static principle

When tied arch bridges with vertical hangers of arch supports elastic to rigid track support. This design works best with a load uniformly distributed in the longitudinal direction and undergoes only relatively small deflections. On the other hand it comes with half side load at relatively large deformations, because the bow dodges in the longitudinal direction and thereby lose the hangers effect. This results in the bow and bottom chord greater bending moments and a significant reduction of the buckling load of the arc.

The oblique arrangement of the hangers in network arch bridges counteracts the deflection of the arc in the longitudinal direction with unidirectional load and increases the buckling load of the arc significantly. The bow is held with unidirectional load approximately in the direction in which he wants to escape, elastic of the hangers. Because the hangers are attached in acute angle at road carrier, a part of the forces is introduced in the horizontal direction in the track support and offset from it by its axial stiffness. Due to the inclined hangers with multiple intersections, a network arch bridge in the longitudinal direction thus behaves both full load and for half-page load similar to a timber where the majority of pure train and compressive forces occur.

The arrangement of the trailer determines the properties of a network arch. It is defined via hangers number, inclination and distance. An easy way to make an efficient structure, the application of a radial hanger assembly has been developed by Benjamin Brunn and Frank Schanack 2003. In the radial hanger arrangement, the distances of the upper hanger nodes and the angle between hangers and bow are constant.

By using a hanger network with monotonically increasing slope of the trailer, as proposed by Per Tveit, a comparable efficiency can be achieved to a radial arrangement with shorter trailers. The first trailer of a trailer sets then receives a predefined start angle is increased continuously for the next trailer.

Studies show that it comes in both solutions above, provided optimum tilt angle no defaults of hangers. The maximum forces in the hangers and the stress ranges can be reduced and there are only minor differences between the hanger maximum forces.

Demarcation to Nielsen Lohse bridge

In Japan, tied arch bridges are crossed hangers mistakenly called Nielsen - Lohse bridges. Nielsen stands for the engineer Octavius ​​F. Nielsen, who filed a patent on sheets with drawstring and inclined hanger rods in 1926. This bridge type was then about 60 times realized mainly in Sweden. None of these bridges, there are cross-over suspension rods.

Lohse is the German engineer Hermann Lohse (* 1815, † 1893), the end of the 19th century a bow with drawstring developed whose drawstring opposite to the bow is curved. The roadway carries a third element that hangs under the arches.

It will thus be seen that the name Nielsen - Lohse for rod bends with multiple crossed hangers is not correct. In addition, the model of the Japanese network arch bridges is the Fehmarn bridge whose design is based in turn on the network arch.

The correct name of tied arch bridges with inclined and easily crossed hangers is Nielsen - bridge. Tied arch bridges with multiple crossed hangers are network arch bridges. This strict rule is justified because it leads to a more efficient structure.

Examples

• Bolstadstraumenbrücke, Norway ( 1963)
• Fehmarnsundbrücke, Germany (1963 )
• Oderbrücke Frankfurt (railway), Germany (2008)
• Providence River Bridge, USA (opening planned for 2008 )
• Steinkjerbrücke, Norway ( 1963)
• Rose Valley Bridge Plauen (railway), Germany (2008)
• Flora Haldensleben Bridge (railway), Germany (2010)
• Network arch bridge in Bechyně, Czech Republic ( 2004) ( wingspan: 41 m )

Nielsen bridges

• Main Bridge Niederberghaus -Sulzbach, Germany (2001)
• North Bridge Marktheidenfeld, Germany (2002)