The first bridges with a structure of load-bearing iron elements were suspension bridges. The idea of a suspended bridge is extremely old; the first known footbridge, using suspension chains, was constructed in China around 65 A.D. However, until the end of the 18th century, very few bridges were constructed from metal. The weight of the chains limited spans to around 20 m, and only the invention of chains made of articulated iron bars, known as eye bars and patented in England in 1817, allowed spans to substantially increase. The first important suspension bridge by the Englishman, Telford, was constructed over the Menai Straits in 1826 and is noteworthy for achieving a record span of 176 m. This bridge is still in service, the original iron chains having been replaced by articulated steel bars in 1938.
Towards the end of the 18th century, in 1779 to be precise, the first cast iron bridge appeared over the Severn at Coalbrookdale in England. Conceived and constructed by a blacksmith named Abraham Darby, the bridge comprises five arches of 30 m span. Other cast iron arch bridges were constructed at the end of the 18th century and the beginning of the 19th century, such as the bridge at Sunderland (Great Britain) with a span of 72 m (1796).
Parallel with these developments suspension bridges progressed with the adoption of cables to replace chains, once and for all. This solution is credited to a Frenchman, Seguin. The first use of cables dates back to 1816, by an Englishman, Rees, while the Swiss, Dufour, undertook systematic testing of cables between 1823 and 1824. In 1823 he completed the first suspension bridge in continental Europe, the St-Antoine-Geneva footbridge for pedestrians, comprising two 40 m spans.
A record for the longest single span, indeed a record that stood for many years, was established inEurope by the suspension bridge at Fribourg (CH) with a span of 265 m. This was constructed by a Frenchman, Joseph Chaley, in 1834 and demolished in 1930. Only one suspension bridge of this era is still in existence in continental Europe: the Pont de la Caille over the ravine des Usses in Savoy, credited to Belin in 1839, spanning 192 m.
At the beginning of the 19th century, practical and robust procedures were developed for the industrial production of rolled plates (1830). These permitted more economical and easier construction of large structures by riveting. An important improvement for the cables was developed by a Frenchman, Arnodin, who perfected the fabrication of double-spiral (alternately wound) steel wire ropes around 1880, which replaced, once and for all, the previous solutions with parallel wires. Cast iron, a relatively brittle material, did not lend itself to the construction of beam bridges. It was only towards the middle of the 19th century that the first examples of such bridges appeared, with the development of wrought iron (which is notably better in tension) for use on an industrial scale. One of the first great beam bridges was the Britannia in Wales, which entered service in 1850. With two main spans of 146 m, this beam bridge had a closed cross section in the form of a rectangular box inside which passed a railway line. It was replaced in 1971 by a bridge with a structure of steel truss arches.
Wrought iron had thereby replaced cast iron for large span arches. The most spectacular example of this form of construction was the Viaduc de Garabit, constructed by the team of Gustav Eiffel in 1884. The total length of 564 m includes a triangulated arch of 165 m span and rise of 52 m. It was erected using the cantilever method, spanning out from the supports. Development of the industrial fabrication of steel followed the invention of the Bessemer converter in 1856 and the Siemens-Martin process in 1864. Due to its mechanical properties, and in particular its improved tensile behaviour, steel went on to entirely replace both cast iron and wrought iron. The era of steel bridges in Europe began with the Firth of Forth, which adopts truss beams, of variable depth and extremely rigid. Constructed between 1881 and 1890, this bridge comprises two central spans of 521 m and two side spans of 207 m each. The central spans comprise two cantilevers, each of 207 m, supporting between them a beam of 107 m span. This system, know simply as “cantilever”, was subsequently adopted for a large number of similar bridges.
The first developments of long span bridges in the United States are credited to John A. Roebling. One of the most notable is the first suspension bridge crossing the deep gorge downstream of the Niagara Falls. Completed in 1855 this bridge had a span of 250 m and was constructed in two stages – firstly for a railway and secondly for horse drawn carriages. It was demolished in 1896. During this period (1877) electric arc welding was discovered. Alongside the ever increasing ability to produce thicker steel plates, this new joining method allowed, later on in the second half of the twentieth century, the fabrication of the solid web beams (plate girders) widely used today. John A. Roebling was also the father of the Brooklyn suspension bridge across the East river in New York, which entered service in 1883. Its span of 487 m set a world record at the time, and was achieved thanks to the first use of steel cables. This bridge was also original in the form of the cables, which combined suspension cables and cable stays in a form known as “hybrid”.
For a long time the United States was known as the country of long span suspension bridges, particularly due to the works of the Swiss engineer, Othmar H. Ammann. He was the first to achieve a span exceeding 1000 m, with the George Washington Bridge, which crosses the Hudson River in New York. This was inaugurated in 1932 with a span of 1067 m and had a second deck added in 1962. The magnificent Golden Gate Bridge was inaugurated five years later with a span of 1280 m. Specific studies of the aerodynamic performance of suspension bridges were undertaken following the collapse of the Tacoma Bridge, which was destroyed in 1940 due to the resonance of its deck in adverse wind conditions. These studies led to the adoption of decks comprising large truss box girders. In addition to their aerodynamic advantages, the use of such boxes facilitated the construction of twin deck bridges using beams between 10 m to 12 m deep, and carrying traffic on the upper and lower flanges of the box girders. The Verrazano-Narrows Bridge at the entrance to New York, also the work of Ammann, was conceived in this way and inaugurated in 1964. This suspension bridge held the world record until 1981 at a span of 1298 m.
That record for longest span was finally beaten in 1981 by the Humber Suspension Bridge in Great Britain. This bridge has a span of 1410 m, and its deck adopted a new form, comprising a box girder with an aerodynamic shape to significantly reduce the effects of wind. However, this modern form of deck has not been used in Japan where large suspension bridges are still constructed using box girder trusses (mainly due to the need to separate railway and road traffic on double decks). Most of the long span suspension bridges in Japan link the islands of Honshu and Shikoku. One of them, the Akashi Kaikyo Bridge, has held the world record for longest span since its inauguration in 1998, with a central span of 1991 m.
In the world of arch bridges, it is worth considering some notable examples, such as the New River Gorge Bridge in the United States, constructed in 1977 with a span of 518 m; the bridge at Bayonne in the United States (1931 and 504 m); and Sydney Harbour Bridge in Australia (1932 and 503 m). Since 2003 the Lupu Bridge in China spanning 550 m has held the record for a steel arch bridge.
Of final note is the spectacular growth in the use of cable stayed bridges since the middle of the 20th century. Developments in materials (high strength steels), methods of calculation by computer, and the capacity of lifting equipment used for erection have all contributed to this trend. As an example, in 1957 the longest span for a cable stayed bridge was 260 m for the Theodor Heuss Bridge in Dusseldorf, Germany. By the end of the 1980s, the longest spans were between 400 and 500 m, which included numerous bridges in Thailand (Rama IX, 450m, 1987), Japan (Yokohama Bay, 460 m, 1989) and Canada (Annacis Island, 465 m, 1986). During the final years of the millennium, the record for longest span was toppled with increasing frequency: reaching 856 m in 1995 with the Pont de Normandie in France, then 890 m in 1999 with the Tatara Bridge in Japan. Now cable stayed bridges are competing in the span range that was previously the exclusive domain of suspension bridges.
Another evolution is the use of multiple span cable stayed bridges. The most notable example of this type of structure is the Viaduc de Millau in France, which was opened in 2004. Conceived by Michel Virlogeux, it comprises eight cable stayed spans, of which six spans reach 342 m [3.2]. In Switzerland a number of noteworthy steel and composite bridges were constructed as part of the development of the freeway (autoroute) network. Examples include the composite bridge over the Veveyse near Vevey (1968), which comprises a 5 m deep steel box girder with spans of 58 m, 129 m and 111 m [3.3]. Additionally, there are the bridges over the Rhone at St Maurice (1986), which are cable stayed composite bridges spanning 100 m. More recently, two important and innovative bridges have been constructed on the Yverdon-Berne section of freeway A1. The Viaduc des Vaux (1999) is a box girder composite bridge with spans of 130 m. It was launched despite its complex S shape geometry plan. The Viaduc de Lully (1995) is a composite bridge that adopts space frame steel trusses. A particularity of this bridge is that the trusses are formed from thick walled tubes welded to each other without the use of gusset plates.
Europe is currently experiencing a kind of renaissance in steel and composite bridges of small to medium span. This puts an end to an era in which the vast majority of this type of structure was constructed using reinforced or prestressed concrete. Part of this change is due to improvements in methods of fabrication, such as automatic welding, and the numerically controlled cutting of plates. It is also due to the development of high strength steels with improved characteristics for welding. Developments in lifting equipment, for both the workshop and on site, now allow prefabrication of elements of considerable weight. The adoption of these larger elements can greatly simplify the work needed on site and thereby significantly reduce the time needed on site.
For these various reasons, composite bridges, and in particular twin beam composite bridges, appear likely to continue to see widespread uptake for several decades in the world of short and medium span bridges. This will be true for both road and railway bridges. Already of note is a significant increase in the use of twin beam composite bridges in Japan since the beginning of the 2000s, and some very nice bridges on the TGV (high speed train) network in France
Extract of the book: Steel Bridges by Michael Jaccard Published by the Presses Polytechniques et universitaires romandes