Frame and Form

The tubular structure is rarely applied in the design of bridges; is more suited to large roofs in sport or fair pavilions. Today we present an structure difficult to classify that shows an original example of the use of tubular profile in bridge design.

Most probably Jörg Schlaich embodies the archetype of structural designer. He and his team are the masterminds of the Nesenbach Valley Bridge, a hybrid work from the functional point of view, footbridge and roadbridge, and from the structural point of view: integral bridge, ie, jointless and bearingless, and composite deck with tubular metal frame.

This bridge is located on a highway between Stuttgart and the nearby town of Vaihingen. Merge two tunnels that are interrupted when the road crosses the valley of Nesenbach. The distance between the two mouths is 151 m. and during design stage it was decided to join the deck to the support structure of both tunnels, creating a jointless viaduct.

Photo obtained on the website of CIDECT

The main structure of the deck is a truss beam formed in the bottom with steel tubular profiles and at the top by a concrete slab that holds the pavement of the road. The tubular structure is divided into 2 ribs following a triangulation scheme of Warren beam type, but spatial, since in every rib there is a single down tube and two cylindrical profile layouts connecting the tube with the slab (could speak of a tetrahedral beam instead of triangular).

Photo obtained on the website of CIDECT

Bridge piers evoke the figure of a tree. Have also been built with tube profiles;each cell is formed by 4 vertical tubes that are joined at the base and split and bend at the upper part to merge with the truss beam of the deck in 4 different nodes. The nodes between the truss beam and piers are direct, ie,both structures joint without intermediate supports. It is noteworthy that all the nodes of the tubular structure, in piers as in truss beam, are manufactured in cast steel, instead of using the most common procedure for welding a tubular profile against another.

Photo obtained on the website of CIDECT

A truss deck is particularly suitable for bridges with roads at different levels, where the transparency of the triangular structure usually allows you to place a driveway at the top of the truss and another one in the lower. However, en el Nesenbachtalbrücke se ha optado por situar un camino peatonal y ciclista sobre una estructura auxiliar e indipendiente de la celosía principal que está formada por una serie de arcos tubulares que envuelven la carretera y se apoyan en los bordes de la losa.

Photo by AndH obtained from Panoramio

Photo by Cuberg obtained from Panoramio

Apart from supporting the road, the arches give formal continuity to the section of the tunnel and allow the placement of stainless steel panels that act as noise barrier.

Photo by Sven Gerald Nimeier obtained from Panoramio

Meta-Information:

The Nesenbach Valley Bridge on the web of Schlaich, inStructurae (contains 13 photos) and Cidect (There are other examples of bridges with tubular frame).

Instituto de la Construcción Tubular ICT

International Committee for the Development and Study of Tubular Construction CIDECT

Articles about integral bridges (in spanish): Javier Rui-Wamba article in ROP, Javier Torrico (from Fhecor Ingenieros) article .