Orthotropic plate

Manufacture of parts of an orthotropic plate

An orthotropic plate is a component used in bridge construction as a roadway plate , which consists of a structural steel plate that is stiffened on the underside with welded steel profiles in the longitudinal and transverse directions. The orthotropic plate is used as a cover plate for box girder bridges or T-beam bridges in steel construction, as a roadway girder for suspension bridges and cable-stayed bridges as well as for movable bridges . The stiffeners prevent local deflections so that point loads are better distributed in the structure. The orthotropic plate is particularly light compared to other equivalent constructions, but expensive to manufacture and sensitive to errors in the detailed construction. It is also known as a lightweight steel roadway.

Origin of the term

The name is formed from the two technical terms orthogonal and anisotropic from strength theory . A sheet metal plate without stiffening elements would have an isotropic behavior, i.e. it would show the same force-deformation behavior regardless of the direction of load. The stiffening elements give the plate a force-deformation behavior that depends on the direction of load, so that its properties are no longer isotropic, which is called anisotropic in technical language . Since the two stiffeners are at right angles - orthogonal in technical terms - to each other, the plate has an orthogonal-anisotropic behavior or, if the two terms are drawn together, an orthotropic behavior.

history

Bottom view of the box girder of the Deutz bridge , which is provided with an orthotropic deck slab above and overhang

Bottom view of the orthotropic plate of the Mülheim bridge

The first constructions go back to the 1920s. In America, steel plates were used to build movable bridges , which were stiffened with riveted steel girders. In 1938 the American Institute for Steel Construction (AISC) published the first reports on a construction known as the Battle Deck Floor , which is built up similar to a deck on battleships . It consists of a steel cover plate, which is supported by double T-beams.

After the Second World War , in 1948 the German engineer Wilhelm Cornelius , who worked at MAN , received a patent for a road bridge with flat sheet metal , which contained the description of the orthotropic plate. The technology was first used on the Deutz Bridge , which opened in 1948 , whose superstructure consisted of a steel box girder with an orthotropic cover plate. The Mülheim Bridge , which opened in 1951, was the first to use an orthotropic T- beam . The Weser Bridge in Porta Westfalica followed in 1954 as a steel box girder bridge with an orthotropic deck.

The orthotropic plate was lighter than the already known constructions. This saved construction material and weight, and particularly slim bridges with large spans could be built.

In the late 1960s and early 1970s, four steel box girder bridges with orthotropic slabs collapsed during the construction phase: the Koblenz South Bridge , the Prater Bridge , the Cleddau Bridge and the West Gate Bridge . The apparent connection between these collapses led to an overreaction in the professional world and to an extremely critical assessment of these structures, whereby the orthotropic plate was not to blame for the collapses and two of the four collapses were caused by unsuitable procedures during the construction phase. However, it turned out that the construction of bridges with orthotropic plates is demanding and particularly sensitive to errors in construction details. Early designs often used a cover plate that was too thin.

For general applications, the construction with orthotropic deck slabs has been replaced by concrete girder bridges, which can be constructed more cost-effectively because expensive welding work is no longer necessary. In addition, concrete bridges can be built on site without prefabricated parts if required. Orthotropic deck girders are now only used for bridges where weight plays a decisive role, such as moving bridges or long cable-stayed and suspension bridges.

Older bridges with orthotropic slabs are often no longer able to cope with the increased traffic loads and have to be extensively renovated. One possibility for renovation is to apply a new road surface, which distributes the loads better on the orthotropic slab and additionally stiffens it.

Structure and function of the structure

The orthotropic plate consists of the cover plate, the longitudinal ribs welded on underneath and the cross members.

Cover plate

The cover plate can be 10 to 15 mm thick and is covered with a road surface made of mastic asphalt , which is usually about 60 mm thick. The mastic asphalt protects the cover plate from corrosion and distributes the upright forces of vehicle wheels better on the structure. The cover plate acts as a flange for both the longitudinal ribs and the transverse webs . When using an orthotropic plate in a steel T- beam bridge, the cover plate is also an upper chord for the longitudinal girders.

Remnants of the carriageway slab of the old Haseltal bridge with stiffening V-profiles

Longitudinal ribs

The longitudinal ribs usually have a trapezoidal cross-section and are welded onto the underside of the cover plate with two weld seams. They are usually between 6 and 10 mm thick and enclose a cavity with the cover plate, the strength of which is similar to that of a hollow box and makes the orthotropic plate torsionally stiff. The longitudinal ribs sometimes have openings on the underside that allow access to the screws that hold the individual bridge segments together.

Instead of the trapezoidal ribs, other, less suitable profiles were used, mostly with the aim of circumventing patents . The cross-sections used were U-profiles , V-profiles or champagne flute profiles . The latter required four times more welding than the other profiles.

Originally, I, L and T profiles were used in which the cover sheet and the longitudinal rib did not form a closed cavity. These constructions are torsionally softer compared to the construction with closed longitudinal ribs, but could be calculated more easily. In addition, the underside of the cover plate is less well protected against corrosion, since a larger area is exposed to the air compared to orthotropic plates with closed profiles.

Crossbars

In the case of orthotropic panels with open ribs, the cross members are arranged at a distance of 1.5 to 2.5 m, for those with closed ribs at a distance of 3 to 5 m. The cross members are provided with cutouts to allow the ribs to pass. The ribs are welded to the cross members; only in the lower area of ​​the rib is the weld sometimes omitted and the recess there dimensioned so large that the rib is not touched, thereby avoiding constraint stresses between the rib and cross member when the plate is bent in the longitudinal direction.

The transverse webs on the one hand support the cover plate in the transverse direction, but together with the longitudinal ribs also form a grate that increases the strength of the plate.

Applications

Orthotropic deck slabs are also used in bridges where weight plays a very important role, such as moving bridges or long cable-stayed and suspension bridges. Compared to pure concrete structures, orthotropic slabs can save up to a quarter of the weight of such bridges, since both the roadway girders and load-bearing parts are lighter.

Orthotropic slabs can also be used to reinforce existing bridges by replacing the existing concrete deck with an orthotropic slab.

Since the lighter construction has less heat capacity, it cools down faster - due to radiation or wind - and condensation and ice can develop more quickly on its roadway. But it also heats up again more quickly.

Selected examples of bridges with orthotropic deck slabs

Surname	place	country	Year of completion	image	comment
Akashi Kaikyō Bridge	Awaji and Kobe	Japan	1998		Longest suspension bridge in the world
Viaduc de Millau	Millau	France	2004		Cable-stayed bridge with the largest orthotropic girder in the world
Pont Gustave Flaubert	Rouen	France	2008		Lift bridge in the port entrance of Rouen
Golden Gate Bridge	San Francisco	United States	1937 (1986)		Example of a bridge, the existing deck of which was replaced by an orthotropic deck to relieve the construction
Nordhordlandsbrua	Vestland	Norway	1994		Cable-stayed bridge combined with a floating bridge
Mülheimer Bridge	Cologne	Germany	1951		First bridge in Germany with an orthotropic deck
Theodor Heuss Bridge	Dusseldorf	Germany	1957		Bridge of the Düsseldorf bridge family , Germany's first cable-stayed bridge
Second Weser bridge in Porta Westfalica	Porta Westfalica	Germany	1954		First steel box girder bridge with orthotropic deck slab in Europe and, upon completion, the largest fully welded steel superstructure in Europe, demolished in 1995
Europabrücke (Brenner motorway)	near Innsbruck	Austria	1963
St. Alban Bridge	Basel	Switzerland	1955		Demolished in 1973 and replaced by the Black Forest Bridge

literature

• A. Mangus, Sun Shawn, Wai-Fah Chen, Lian Duan: Bridge Engineering Handbook . 1st edition. CRC Press, Boca Raton, Florida 1999, chap. 14: Orthotropic Deck Bridges ( freeit.free.fr [PDF]).
• Karl-Eugen Kurrer : History of Structural Analysis. In search of balance. Ernst and Son, Berlin 2016, ISBN 978-3-433-03134-6 , pp. 606–618.
• Karl-Eugen Kurrer: On the history of the orthotropic bridge deck. In: Progress in Steel and Composite Structures. Edited by B. Gosowski, K. Rykaluk, J. Ziółko. DOLNOŚLĄSKIE WYDAWNICTWO EDUKACYJNE, Wrocław 2011, ISBN 978-83-7125-203-7 , pp. 52-65.
• Karl-Eugen Kurrer: Evolution de la dalle orthotrope in la construction de ponts métalliques. In: L'architrave, le plancher, la plate-forme. Nouvelle histoire de la construction sous la direction de Roberto Gargiani. Presses polytechniques et universitaires romandes Lausanne, Lausanne 2012, ISBN 978-2-880-74893-7 , pp. 686-695.

Web links

Wiktionary: orthotropic plate  - explanations of meanings, word origins, synonyms, translations

Commons : orthotropic disk  - collection of images, videos and audio files

• Repair of orthotropic road slabs. (PDF, 3.9 MB) Federal Highway Research Institute, October 19, 2005, accessed on September 21, 2013 . 
• Gerhard Sedlacek, Michael Paschen: Investigation into the sustainable repair of orthotropic road slabs. (PDF, 2.4 MB) Sedlacek & Partner, accessed on September 21, 2013 . 
• Manual for design, construction, and maintenance of orthotropic steel deck bridges. (PDF, 10.4 MB) Federal Highway Administration , February 2012, accessed September 21, 2013 . 
• Alfred R. Mangus: A Fresh Look at Orthotropic Technology. Federal Highway Administration , 2005, accessed September 21, 2013 . 
• Alfred R. Mangus: Orthotropic Steel Deck Bridges Landmarks of our Infrastructure in California 1965–2009. (PDF) Caltrans, September 21, 2009, accessed on September 21, 2013 . 

Individual evidence

1. ↑ Patent DE847014 : Road bridge with flat sheet metal. Published October 2, 1952 , inventor: Wilhelm Cornelius. ‌
2. ↑ Steel Continuous Girder Bridges. (No longer available online.) NISEE, archived from the original on September 13, 2014 ; accessed on October 6, 2013 . 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.  
3. ^ Leonhardt, Fritz (1909-1999). (No longer available online.) In: great-engineers.de. Brandenburg University of Technology Cottbus , archived from the original on September 22, 2013 ; Retrieved September 13, 2013 . 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.  
4. ^ A. Mangus, Sun Shawn, Wai-Fah Chen, Lian Duan: Bridge Engineering Handbook . 1st edition. CRC Press, Boca Raton Fl 1999, chap. 14: Orthotropic Deck Bridges, p. 38 ( freeit.free.fr [PDF]).
5. ↑ Joachim Scheer: Failure of structures: bridges . John Wiley & Sons, 2000, ISBN 978-3-433-01802-6 ( limited preview in Google Book Search).
6. ↑ Manual for design, construction, and maintenance of orthotropic steel deck bridges. (PDF; 10.4 MB) Federal Highway Administration , February 2012, p. 6 , accessed on September 21, 2013 . 
7. ↑ CONTEC FERROPLAN® system for the renewal and reinforcement of orthotropic steel bridges. Ferroplan, accessed October 5, 2013 . 
8. ↑ Repair of orthotropic road slabs. (PDF; 3.9 MB) Federal Highway Research Institute, October 19, 2005, accessed on September 21, 2013 .