Concrete bridges- today’s modern bridge types you see while travelling. Made of granular materials that is bound together by cement (crushed rock with burnt lime), concrete existed as far back as the period of the Roman Empire and used for infrastructures and buildings, many of which can still be found today when travelling through the regions of southern and eastern Europe once dominated by the likes of Caesar. Concrete was first used for closed spandrel arch bridges, but its expanded usage can be found in the first three decades of the 20th century, when concrete was used for open spandrel arches, Marsh arches, slabs, girders and Luten arches- with the oval shaped arch span.
In Germany, concrete was used for the Autobahn motorways in the 1920s with several concrete slabs resembling square-shaped arches being built along the highway connecting Berlin and Munich. But they were not the only types that were used. In 1938, shortly before the start of World War II, a new concrete bridge type was introduced in the German state of North Rhine-Westphalia: the prestressed, pretensioned concrete girder bridge, known to Germans as the Spannbetonbrücke. The concept was invented by a French engineer, Eugéne Freyssinet (1879- 1962), where tensile steel rods are inserted into the concrete bridge to provide compressive stress as a complement to tensile stress that is normally exerted onto the concrete through live load on the bridge as well as through weather extremities (concrete expanding in warm weather and compressing in cold weather).
The concept was first used on an Autobahn overpass between Beckum and Oelde, located near the cities of Hamm and Münster in eastern North Rhine-Westphalia. There four different girders were assembled in a way that they were placed in a prestressed steel encasing and supported by I-beam suspenders. They were then fasted together and placed over the Autobahn A2, and crossing was open to traffic on 12 November, 1938. Albeit the bridge was 40 meters long, this concept was later used for spans up to three times the length. Gotthard Franz (1904-1991) of the firm Wayss and Freitag oversaw the construction using the Freyssinet concept, together with the French engineer himself, who later built several bridges of this kind, including the Railway Station Bridge in Aue (Saxony) as well as bridges in Hamburg, Kiel and Brunsbuttel (near the Baltic-North Sea Canal). The concept was later used in other countries, including the US, where one can see many of these bridges built from the 1980s onwards crossing ravines and roads today.
The Beckum-Oelde (Hesseler Weg) Overpass served traffic for 74 years until it was relocated to a rest area last year. Because it was declared a national technical landmark (technische Denkmal) in 1991, the demolition of the bridge was not allowed. Today, one can see the historic landmark, hoisted by two modern concrete piers at the rest area in Vellern-Süd. The overpass signaled the beginning of innovation and proliferation of concrete bridges, something that would happen beginning in the 1950s, when the shortage of steel because of its usage in World War combined with the destruction of steel mills in Germany and Europe prompted the creativity of engineers to find ways to build crossings using other materials. Concrete was cheap and using the design of inventors like Freyssinet, the 1950s marked the beginning of the proliferation of concrete bridges, first used to replace structures destroyed in the war, and later used to replaced functionally obsolete bridges made of iron and steel, as seen in the US and Canada. While Freyssinet is not to blame for the invention but more to thank for ushering the era of concrete bridges, we have the honor of introducing the age of modernization, something that we still see today on our city streets and highways.
Author’s note: Nicolas Janberg wrote an article about this bridge, which you can click here. The bridge is one of many listed as candidates for the 2013 Ammann Awards for Bridge of the Year and Best Example of a Preserved Historic Bridge. Thanks to Frank Selke for the use of his photo.