Lattice girder

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Schematic representation
Lattice girder made of wood
Town québécois : Pont Bordeleau
Kew Railway Bridge, wrought iron lattice girder
Cubzac road bridge

A lattice girder consists of a large number of parallel bars that are placed diagonally on top of each other and connected to one another at the crossing points to form a lattice . The upper and lower edges of the girder are usually formed by continuous straps . This construction method can be viewed as a truss with continuous bars. Colloquially, the terms truss and lattice girders are often used synonymously.

This type of lattice girder should not be confused with the lattice girders of lattice girder ceilings or walls that are specially manufactured for this type of construction and approved by the building authorities .

Lattice girders were traditionally mostly made of wood , with light wooden slats and wooden nails as connecting means. The use of wooden slats instead of solid wooden beams offers economic advantages. Today, wooden lattice girders are no longer used due to the labor involved in their manufacture. Alternatively, glulam beams are often used, which can be produced (semi) automatically.

Wooden bridges

In the US, this method of construction was in 1820 and 1835 by the American architect Ithiel Town as Town's lattice truss patented in German as Town shear bar carrier or Town'scher Staff carrier designated. It was used in particular in the USA and Canada for the construction of covered wooden bridges . In Québec , the Ministère de la Colonization du Québec (roughly: Ministry of Agriculture) introduced a more cost-effective further development in 1905 with narrower slats and metallic connections instead of wooden nails. The girders were provided with vertical posts every 8 feet for better stabilization. This variant, known as Town québécois , was built until the 1950s. Numerous bridges using lattice girders are still preserved today.

Iron bridges

With the widespread introduction of wrought iron produced by the puddle process from Great Britain , the principle was transferred to wrought iron lattice girder bridges. This construction method was used from 1847, mainly in the 1860s and occasionally until around 1900. Instead of the slats, flat iron reinforced with angle iron were used. With the introduction of rolled profiles and the improvement of calculation methods, the grids became wider, and the grids were mostly reinforced by posts. The more reliable methods of static calculation of trusses and the development of the market towards commercially available, standardized profile girders ultimately led to the lattice girders being replaced by trusses . No exact delimitation was made, many of the later bridges were referred to as both lattice girder and truss bridges.

Some of the still existing wrought iron lattice girder bridges are:

The construction method was replaced by the introduction of steel girders , which were manufactured industrially in large quantities, which allowed the more cost-effective production of truss bridges .

In the 1953–1954 rebuilt, double-track Urmitzer railway bridge , the construction method was used again for a steel bridge.

Halls

Imperial War Museum, Duxford, with lattice girders under the hall roof

A similar joining principle is based on lattice shell constructions such as the Multihalle in Mannheim. These also consist of light rods that are fixed at the crossing points. Since they are part of a curved lattice shell , the bars are slightly curved in contrast to the usual lattice girder.

Starting in 1866 , an Irish company developed the so-called Belfast truss , a lattice girder with a curved top chord as a support for wide-span hall roofs.

Web links

Commons : Lattice girders  - collection of images, videos and audio files

Individual evidence

  1. ↑ Jean Lefrançois: Les ponts couverts au Québec, héritage précieux. 2004, p. 8
  2. ^ Lattice girder in Lueger: Lexicon of the entire technology
  3. ^ Friedrich Heinzerling: The bridges in iron. Verlag von Otto Spamer, Leipzig 1870, p. 267 ( digitized on Google Books)
  4. ↑ In the List of lattice girder bridges in the United Kingdom in the English Wikipedia a number of other lattice girder bridges are listed.