From the very beginning, Professor Leonhardt and his firm have been attracted by the design of bridges.  Today, about 45% of the firm’s billings correspond to the design, checking and on-site supervision of bridges, and nothing else has contributed so much to the firm’s worldwide reputation.

      The aim of Professor Leonhardt and his collaborators has always been to design aesthetically pleasing bridges, and the experience of more than 40 years of professional work on this subject is documented in this book with the text in both German and English:

      Leonhardt, F.: Brücken, Ästhetik und Gestalting - Bridges, Aesthetics and Design, Deutsche Verlags-Anstalt, Stuttgart, 1982.  (In the U.S.: The MIT Press, 28 Carlton Street, Cambridge, Mass 02142)

      Due to his Professorship in Concrete Structures and his book on Prestressed Concrete, Professor Leonhardt is sometimes considered primarily a designer in concrete.  However, from the beginning, he and his firm have designed numerous steel bridges of all types.

• Continuous Girder Bridges
• Arch Bridges
• Suspension Bridges

      To study the concrete bridges of Leonhardt, Andrä and Partners is to study the history, the present and the future of prestressed concrete bridges.
      The first bridge of this type, designed in 1949, had a span of only 30 meters.  The first large bridge, the bridge over the Neckar Canal at Heilbronn, with a main span of 96 meters, was designed in 1950.  Recently, the design for the largest prestressed concrete railway bridge in the world (mainspan 135 meters) was completed.

• Continuous Girder Bridges
• Frame Bridges
• Arch Bridges

      Stayed bridges were built as early as the 17th and 18th centuries.  As at that time neither precise calculation methods nor adequate tension members were available, some bridges collapsed and the system disappeared for about two centuries.
      After their reappearance in the mid-1950’s, cable-stayed bridges almost completely replaced the competing systems, suspension bridges and arch bridges.  Compared with ground-anchored suspension bridges, they are stiffer and require less material, especially for cable and abutments.  Compared with self-anchored suspension bridges and arch bridges, their erection is much easier.
      Along with the progress in computer analysis, the structural system developed from few cables to multi-cable arrangements, offering advantages in construction, in the complete structure, and in maintenance.
      Whereas in early cable-stayed bridges the deck and towers were of steel, today towers are normally of concrete.  The decks of highway bridges up to 700 meters span and of railway bridges up to 500 meters span can also advantageously be built in concrete.
      Leonhardt, Andrä and Partners took a very active part in the development of cable-stayed bridges from the beginning by practical design, theoretical studies, and improvement of cables.  Design have been made for bridges with steel, composite and concrete decks, and for spans ranging from a modest 60 meters to 1800 meters.
      The following are the most important general publications written by members of Leonhardt, Andrä and Partners related to this development:

1. Leonhardt, F., and Zellner, W.:  “Cable-Stayed Bridges, Report on Latest Developments,”  Canadian Structural Engineering Conference Proceedings, 1970.
2. Leonhardt, F., and Zellner, W.:  “Comparative Investigations between Suspension Bridges and Cable-Stayed Bridges for Spans Exceeding 600 meters,”  IABSE-Publications, Vol. 32-I/1972, Zürich, pp 127-165.
3. Leonhardt, F., Andrä, W., and Zellner, W.:  “Entwicklung von weitgespannten Schrägkabelbrücken (Development of Longspan Cable-Stayed Bridges),”  in Beyer, E., and Lang, K.:  Verkehrsbauten.  Beton-Verlag, Düsseldorf, 1974, pp 77-95.
4. Leonhardt, F.:  “Latest Developments of Cable-Stayed Bridges for Long Spans,”  Bygningsstatiske Meddelelser 45 (1974), No. 4, Lingby, Denmark, pp 89-143.
5. Leonhardt, F., and Zellner, W.:  “Cable-Stayed Bridges,”  IABSE Surveys S-13/1980, Zürich, pp 21-48.
6. Zellner, W., and Svensson, H.:  “Zur Entwicklung der Schrägkabelbrücken aus Beton (On the Development of Cable-Stayed Concrete Bridges).”  Spannbetonbau in der Bundesrepublik Deutschland 1978-1982.  Deutscher Beton-Verein e.V., s.p.23 FIP 9th Congress, Stockholm, 1982, pp 81-95.

• Cable-Stayed Bridges with Steel Deck
• Cable-Stayed Bridges with Composite Deck
• Cable-Stayed Bridges with Concrete Deck

• General
• Examples

• Movable Bridges across Shipping Lanes
• Pedestrian Bridges

      With the ever increasing number of bridges, improved designs and construction methods are necessary in order to reduce maintenance costs.  Also, well designed and well constructed bridges are endangered due to:

• air pollution, mainly by CO₂ and SO₂.
• de-icing salt spray.
• traffic impact at expansion joints.
• extreme temperature changes.
• collision by vehicles passing underneath the bridges, especially by ships as they have grown in size and number.
• earthquakes.

      Leonhardt, Andrä and Partners started very early to analyze the causes and to suggest remedies for these damages.  The following is a short selection of the many references devoted to this topic:

1. Leonhardt, F,. Kolbe, G. and Peter, J.:  “Temperaturunterschiede gefährden Spannbetonbrücken (Temperature Gradients Jeopardize Prestressed Concrete Bridges),”  Beton- und Stahlbetonbau 60 (1965), pp 157-163.
2. Leonhardt, F., and Lippoth, W.:  “Folgerungen aus Schäden an Spannbetonbrücken (Consequences of Damage on Prestressed Concrete Bridges),”  Beton- und Stahlbetonbau 65 (1970), pp 231-244.
3. Leonhardt, F.:  “Rissebeschränkung (Crack Limitation),”  Beton- und Stahlbetonbau 71 (1976), pp 14-20.
4. Leonhardt, F.:  “Risschäden an Betonbrücken - Ursachen und Abhilfe (Damage due to Cracks in Concrete Bridges - Causes and Remedies).”  Beton- und Stahlbetonbau 74 (1979), pp 36-44.
5. Zellner, W. and Saul, R.:  “Über Erfahrungen beim Umbau und Sanieren von Brücken (On Experience Gathered in the Remodeling and Restoration of Bridges),”  To appear soon in ‘Die Bautechnik’.
6. Saul, R. and Stevenson, H.:  “On the Theory of Ship Collision against Bridge Piers,”  IABSE Proceedings P-51/1982, pp 29-38.
7. Saul, R. and Stevenson, H.:  “Means of Reducing the Consequences of Ship Collision with Bridges and Offshore Structures,”  Introductory Paper to Theme D ‘Evaluation of Consequences of Collisions’, IABSE International Colloquium on Ship Collision with Bridges and Offshore Structures.  Copenhagen, Denmark, May 30-June 2, 1983.
8. Leonhardt, F.:  “Improving the Seismic Safety of Prestressed Concrete Bridges,”  Journal of the Prestressed Concrete Institute.  Vol. 17 (1972).  No. 6.