Network arch bridge

Fehmarnsund Bridge

A network arch bridge is a tied arch bridge with hangers that cross over each other several times, giving the appearance of a cable network. The inclined hangers reduce bending moments and transverse forces in the arches and the roadway girders when the roadway is unevenly loaded , so that they can be made slimmer. Compared to a classic arched bridge, up to 20% steel can be saved. Typical network arch bridges consist of two parallel arches with a concrete deck slab between them.

history

The Norwegian civil engineer Per Tveit developed the idea of ​​the network arch bridge in the late 1950s. The first network bridge was built in Steinkjer , Norway 1963–1964 and still exists today.

Static principle

The rigid deck girder of tied arch bridges is supported by the arch via vertical hangers (elastic). This design leads to relatively little deflection when the load is evenly distributed in the longitudinal direction. In contrast, if the load is only half-sided, there is comparatively large deformations because the arch gives way in the longitudinal direction and the roadway girder bends in an S-shape. In addition to the resulting bending moments in the arch and lower chord, the buckling load of the arch is significantly reduced.

The inclined arrangement of the hangers in network arch bridges prevents the arch from dodging in the longitudinal direction in the event of one-sided loading and significantly increases the buckling load of the arch. In the event of a one-sided load, the bow is held by the hangers (elastic) approximately in the direction in which it tries to evade. Due to the inclined hangers with multiple crossings, a network arch bridge behaves in the longitudinal direction similar to a lattice girder , in which the creation of bending moments due to the formation of triangular connections is to be avoided.

The arrangement of the hangers determines the properties of a network arch. It is defined by the number, inclination and spacing of hangers. A simple way to create an efficient structure is to use a radial hanger arrangement that was developed by Benjamin Brunn and Frank Schanack in 2003. With the radial hanger arrangement, the distances between the upper hanger nodes and the angles between the hangers and the arch are kept approximately constant.

By using a hanger net with a steadily increasing incline of the hangers, as suggested by Per Tveit, a comparable efficiency to the radial arrangement with shorter hangers can be achieved. The first hanger in a hanger set is given a certain starting angle that is continuously increased for the following hanger.

Investigations show that with both of the solutions mentioned, with optimal angles of inclination, the maximum forces in the hangers and the stress ranges can be reduced and only slight deviations occur between the maximum forces in the hangers .

Differentiation from Nielsen-Lohse bridges

In Japan, tied arch bridges with crossed hangers are called Nielsen-Lohse bridges . Nielsen stands for the engineer Octavius ​​F. Nielsen, who in 1926 applied for a patent on arches with drawstring and inclined hanging rods. This type of bridge was then implemented around 60 times, mainly in Sweden. There are no cross hanging rods on any of these bridges.

Lohse stands for the German engineer Hermann Lohse (1815-1893), who at the end of the 19th century developed a bow with a drawstring, the drawstring of which is curved in the opposite direction to the arch. The roadway carries a third element that hangs under the arches.

The term Nielsen-Lohse for arches with multiple crossed hangers is therefore imprecise. The model for the Japanese network arch bridges is the Fehmarnsund Bridge , the design of which is based on the network arch.

The correct name for tied arch bridges with inclined hangers is Nielsen Bridge , although bridges with simply crossed hangers are mostly counted among the Nielsen bridges today. Tied arch bridges with multiple crossed hangers are network arch bridges.

Examples

• Steinkjer Bridge , Norway (1963)
• Bolstadstraumen bru , Norway (1963)
• Fehmarnsund Bridge , Germany (1963)
• Network arch bridge in Bechyně , Czech Republic (2004)
• Providence River Bridge , USA (2007)
• Oderbrücke Frankfurt (railway) , Germany (2008)
• Rosenbachtalbrücke Plauen (railway) , Germany (2008)
• Flora bridge Haldensleben (railway) , Germany (2010)
• Brandangersundbrua , Norway (2010)
• Lake Champlain Bridge , USA (2011)
• Amelia Earhart Memorial Bridge , USA (2012)
• De Oversteek , Netherlands (2013)
• Osthafenbrücke , Frankfurt a. M., Germany (2013)
• Troja Bridge , Czech Republic (2014)
• Bugrinsky Bridge , Russia (2014)
• John Greenleaf Whittier Bridge , USA (2018)

Nielsen bridges

• Lot Bridge Castelmoron , France (1934)
• Pont de la Coudette , France (1943)
• Main bridge Niedernberg – Sulzbach , Germany (2001)
• Nordbrücke Marktheidenfeld , Germany (2002)

literature

• Per Tveit: An Introduction to the Network Arch . Trondheim 2006 (English, online [PDF]).

Web links

• Per Tveit, Benjamin Brunn, Frank Schanack: Network-Arch. 2010, accessed on June 22, 2013 (English, information about network arch bridges). 
• Per Tveit: Information on the Network Arch. Retrieved June 22, 2013 (English, information about network arch bridges by Per Tveit). 

Individual evidence

1. ^ B. B. Brunn, F. Schanack F., U. Steimann: Network arches for railway bridges . In: Pere Roca Fabregat (Ed.): Arch Bridges IV - Advances in Assessment, Structural Design and Construction . Center Internacional de Mètodes Numèrics en Enginyeria (CIMNE), Barcelona 2004, ISBN 84-95999-63-3 , p. 671-680 ( PDF file ). PDF file ( Memento of the original from September 13, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
2. ↑ S. Pond, W. Graße: Optimization of the Arrangement of Hanger Network Arch Bridges . In: 6th Japanese German Bridge Symposium . Munich.