1.5.1 Masonry Bridges

Apart from the earliest records of bridges, the first appears to be 600 BCE, engineering bridge history may be considered to have been initiated by the Romans. The Romans were the introducers of science in arch construction providing many examples of magnificent masonry bridges and aqueducts such as the ‘Pont du Gard’ in France and ‘Puente de Alcantara’ (Figure 1.18) over the river Tagus, Spain, from the second century [4]. The former is an aqueduct with a total length of 275 m, a maximum depth of 49 m and spans 22 m. The last is a masonry bridge as well, but with spans reaching 28 m and piles reaching 47 m high, appointed the most significant achievement of Roman engineering. Roman bridges are based on the concept of semi‐circular arches, transferring the thrust to piers, and large piers require about one‐third of the spans in multiple arch bridges. The Romans also introduced lime mortar and pozollanic cement for realizing voussoir arches, contributing to increasing span lengths and durability.

Up until the end of the eighteenth century, bridges were built with masonry or wood. Some beautiful examples built along the centuries may still be appreciated, such as Santa Trinita Bridge in Florence (Figure 1.19) built with masonry in the sixteenth century and designed by the architect Bartolomeo Ammanati. While the classical Roman Bridges were made with circular arches, the elegance of Santa Trinita Bridge is due to three flattened elliptic arches, which are the oldest in the world. At the beginning of the twentieth century, in 1905 to be precise, the span record for masonry bridges was reached with the construction of the Plauen Bridge [1, 3], in Germany, which has a main span of 90 m.

1.5.2 Timber Bridges

In the eighteenth century, some remarkable wood bridges were built. In Switzerland, due to a long tradition of wood construction builders, remarkable structures were built, like the Shaffhouse Bridge, designed in 1775 by Grubleman, with two continuous spans of 52 and 59 m. In the USA, one of the most famous wood bridges was built in 1812, over the river Schuylkill with a main span of 104 m, unfortunately destroyed by a fire some years after its construction. Most old timber bridges have disappeared along history; an exception, presently the oldest wooden bridge to our knowledge, is the Kappellbruke (Chapel Bridge) erected originally in 1333 over Lake Lucerne, Switzerland (Figure 1.20). This footbridge was also destroyed by a fire in 1993 and completely rebuilt, standing now as a world heritage site.

1.5.3 Metal Bridges

With the Industrial Revolution of the nineteenth century, metal structures became more and more competitive and, finally, iron and steel started to be used as bridge materials. From this time on, metal truss bridges and suspension bridges were adopted with increasing span lengths.

The first metallic bridge built in the world may be considered to be the Coalbrookdale Bridge [4] with a span of 30 m, designed by Abraham Darby III, a cast iron structure built in Great Britain in 1779. But development had to wait until the end of the nineteenth century, when the prices for steel production has dropped down, to realize the first main steel bridges. One of the most decisive contributions for the development of metal bridges was from Thomas Telford in the nineteenth century. Telford was an English engineer with a large number of relevant projects, always taking aesthetics as a key issue for his work, in parallel with the development of new structural and construction schemes. Craigelachie Bridge, in Scotland, shown in Figure 1.21, is an excellent example of the aesthetical relevance of Telford's design work. In 1826, a famous eye bar wrought iron chain suspension bridge (Figure 1.22), with a main span of 176 m, also from Thomas Telford, was completed in the UK over the Menai Strait, achieving the world record for span length. The iron chain was replaced in 1938 by pin steel bars, allowing the bridge to remain in service up until now. The construction of long span beam bridges is considered to have been initiated with the first box girder bridge in wrought iron, the Britannia Bridge in Wales, UK, built in 1850 by Robert Stephenson (Figure 1.23). The Britannia Bridge, with two main spans of 146 m, had a rectangular cross section with a railroad inside. After a fire in 1970, this famous bridge was modified in 1971 by inserting a truss arch underneath and carrying road and rail traffic, but seriously affecting the architecture of the bridge. The type of box girder solution adopted for the Britannia Bridge was not retained due to the development of truss arch bridges at the end of the nineteenth century.

Reductions in steel prices allowed the increased development of steel arch bridges, or more precisely, wrought iron, with particular reference to long span bridges in the USA. The most famous one was the San Luis Bridge, over the Mississippi, concluded in 1874 with three arches of 152 + 157 + 152 m, and in Europe with several famous arch bridges from the Gustave Eiffel Society. The first relevant Eiffel's bridges were the Maria Pia Bridge in Oporto, Portugal [5], in 1877, and the Viaduc du Gabarit, in France, in 1884. The former (Figure 1.24) 563 m long and with a main span of 160 m, has a truss arch for the railway deck of only 6 m. Particular reference should be made to the erection scheme of the arch using cantilever construction. The Viaduct du Gabarit has a main span arch of 165 m, 52 m rise and a total length of 564 m. This arch was also erected by cantilever as per the Maria Pia Bridge. In 1885, the Belgium engineer Théophile Seyrig, who had worked with Eiffel, designed the Luiz I Bridge [6], also in Oporto and very close to the Maria Pia Bridge. The Luiz I Bridge, an arch bridge, was the largest span in the world at its time – 174.5 m (Figure 1.25a). This bridge with two road decks has a two hinged arch at the base, in spite of its appearance, due to the need of inserting the lower deck. The bridge is located in a classified UNESCO World Heritage Site. A great deal of strengthening of the bridge was done in 2005 (Figure 1.25b), including its arch, truss girder and piers, with an entire replacement of the upper deck with a new steel deck, adapting it for the Metro of Oporto trains (Figure 1.26). The reduction in dead weight of the existing deck, which included concrete and brick elements inserted many years after the original deck, was achieved. The reductions in deck dead load allowed a significant reduction in the strengthening of the arch required for the new functional conditions and required strengthening of the bridge. The design of the upgrading of the bridge was made without affecting its appearance as required by the design and build conditions of the bid.

With the development of industrial production of steel, after the introduction by Henry Bessemer in 1856 of its patent, the Bessemer Converter, transforming cast iron in to the much better steel material, in terms of tensile resistance and ductility, allowed the building of long span trusses in the United States and Europe. The first long span European bridge was the Firth of Forth Bridge (Figure 1.27) built between 1881 and 1890, with two main spans of 521 m and two side spans of 207 m. The two main spans were made with two cantilevers of 207 m supporting a central part made of truss beam 107 m in length. The development of these types of bridges was not unfortunately made without the occurrence of some historical accidents, such as the one occurring in the railway bridge over the river Tay, Scotland, in 1879 and the accident during the erection of the Quebec Bridge, Canada, in 1907. The Quebec Bridge with spans of 549 m was concluded only after a second accident during construction in 1917.

1.5.4 Reinforced and Prestressed Concrete Bridges

The lack of sufficient tensile resistance makes concrete inadequate as a bridge structural material. However, concrete offers the advantage of being a plastic material in the sense that it is poured like fluid in a mould before it hardens, allowing a variety of shapes for beams and piers that could not be achieved in a simple way with steel materials and steel profiles. Some arch bridges with relevant spans, using mass concrete, were made at beginning of the twentieth century, such as the Willeneuve – Sur‐Lot Bridge, in 1919, with an arch span of 97 m, by Eugéne Freyssinet. François Hennebique was one of the first to understand the role of steel reinforcement in concrete to create a suitable bridge material. In 1911, he ‘made’ (Hennebique was more a builder than a designer) the Risorgimento Bridge in Rome, achieving a 100 m span, but the development of reinforced concrete bridges occurred with the work of the great Swiss engineer Robert Maillart who was the first to explore the potentialities of reinforced concrete to build magnificent arch bridges. He explored the concept of relative stiffness between the arch and the deck structure, introducing the concept of Maillart's arch, an arch without bending stiffness, achieved by reducing the stiffness in such a way that the arch follows the pressure line working only under normal forces. However, its thickness is enough to resist to arch buckling. The arch works in this case as the opposite of a cable in a suspension bridge. Among the bridges based on Maillart's arch concept, the longest arch span, 43 m, was the one of the Tshiel Bridge built in 1925. Robert Maillart explored a variety of arch structures from built‐in arches to three‐hinged arches, such as those he adopted for his classical bridge, the Salginatobel Bridge, in Switzerland (Figure 1.28), built in 1930 with a 90 m span. In 1901, Maillart was also the first to adopt a concrete box section for arches, in the Zuoz Bridge with a 30 m span structure. At the beginning, concrete arch bridges were always associated with large wood scaffolding structures, some of them initially developed by R. Coray, built by cantilever construction from each side until the closure at the mid‐section was reached. One may even say the most relevant wood bridges in the world were the scaffolding of concrete arch bridges. A detailed discussion on the historical development of scaffolding structures is presented in the excellent book by Troyano [4].

The concept of multiple arch bridges in reinforced concrete was adopted by Eugéne Freyssinet in 1930, in Plougastel Bridge. This bridge, over the river Elorn in France, is made with three arches of a 186 m span each, following the concepts of previously built multiple arch metal bridges. Many years before, in 1910, Freyssinet designed a beautiful multiple three arch bridge with very flat arches and a rise‐span ratio of only 1/14.7. The arches, each with a 77.5 m span, were initially built as three hinged arches but a few months after completion Freyssinet detected alarming increased deflections at the mid‐span sections due to creep effects in the concrete. He decided to recover the initial shape of the bridge by inserting jacks at the mid span hinge sections and to eliminate these hinges. The beauty of the bridge was the result of the flatness of the arches but also due to the triangulated system adopted to transfer the loads from the deck to the arches. Unfortunately, this bridge was destroyed during the Second World War.

The span lengths of concrete arch bridges were increasing, and one of the largest spans is still the 390 m long arch of the Krk Bridge (Figure 1.29), completed in 1979 in the former Yugoslavia.

Since the end of nineteenth century, the idea of prestressing was always present as a potential scheme to induce initial compressive stresses in concrete and therefore to improve its lack of resistance under tensile stresses. However, it was only in 1928 that Freyssinet decided to concentrate all his activities to explore the potentialities of prestressing for concrete structures. The difficult experience he had with time dependent deformations of concrete in the Veudre Bridge has shown the influence in concrete. Freyssinet understood the need to adopt high strength steel for prestressing and he develop specific systems to anchor prestressing wires or steel bars.

The first long span bridge made in prestressed concrete was the Luzancy Bridge (Figure 1.30) in France, over the river Marne, with a span of 55 m and concluded in 1946. The bridge has been entirely precast in prestressed segmental construction and erected by mechanical devices without any scaffolding. The development of prestressed concrete bridges was very fast in the second half of the twentieth century. Apart from the use of prestressing for prescasting beams, developed in France after the pioneering works of Freyssinet, a special reference should be made to the German contributions in the reconstruction of many bridges after the Second World War. Most of the progress in this field was due to the development of new construction schemes based on the potentialities brought by the prestressing technique in concrete bridges. To achieve large spans avoiding any scaffolding, the idea of cantilever construction of concrete bridges was developed in Germany by Finsterwalder. In 1950, he designed the Balduintein Bridge over the Lahn River with a span of 62 m. It should be noted the cantilever system, a construction scheme adopted since 1874 for steel bridges, was adopted by the first time in concrete bridges for the construction of the bridge over the river Peixe, completed in 1931 in Brazil, with a main span of 68.5 m. The balanced cantilever scheme, in which the bridge is built by cast in‐place segmental construction for each side of each pier allowing for large spans to be reached using simple and small steel equipment, opened a new field in bridge construction technology. The spans quickly increased passing from more than 100 m to reach the main spans of 250 m in several road bridges nowadays. The longest span in full prestressed concrete built by cantilever construction is 301 m in the Stolmasundet Bridge [7], concluded in Norway in 1998. This bridge adopted lightweight concrete in the middle section of the main span to reduce dead weight. Other relevant long span road bridges are the Gateway Bridge in Australia, built in 1985, and the Varodd Bridge in Norway, both with 260 m main spans. In railway bridges, the longest span is the São João Bridge [8], in Oporto, Portugal, a design due to Edgar Cardoso, with a span of 250 m, completed in 1991 (Figure 1.31).

Precasted segmental construction was also a relevant contribution to the development of prestressed concrete bridges, either made by balanced cantilever or with moving scaffoldings to erect the segments. The first bridge with this construction technology was made in 1966 for the Oleron Bridge in France, a long bridge (2900 m) connecting the continent to the island of Oleron, with typical spans of 79 m.

1.5.5 Cable Supported Bridges

Suspension bridges were adopted in the early days of bridge history, namely in pedestrian bridges with natural fibres for the cables. The suspension system was made by a chain of eye bars in cast and wrought iron, already previously referred to with respect to the Menai suspension bridge. But it was the early wire suspension system, adopting wrought iron and strand spinning technology due to John Roebling [9], which gave rise to a new generation of suspension bridges. In 1883, the Brooklyn Bridge, designed by Roebling with a span of 487 m and built in New York, was the first steel wire suspension bridge in the world. At the beginning of the twentieth century, a variety of long span suspension bridges were built in USA. In 1931, George Washington Bridge, designed by the Swiss O. Ammann over the Hudson River in New York, used parallel wire strands rather than rope strand cables and reached a span longer than 1000 m for the first time. This bridge, with a 1067 m main span, doubled the longest existing span but retained this record for only six years when the famous Golden Gate Bridge [9], San Francisco, designed by Joseph Strauss, concluded with a main span of 1280 m.

Contrary to the robustness appearance of the existing suspension bridges at that time, the Tacoma Narrows Bridge was built in 1940, in the state of Washington, with a much slender deck than the typical ones adopted at the time. The main difference was the slender plate girder deck adopted for its superstructure. After a few months in service, the bridge collapsed because of aerodynamic instability under wind action with a much lower wind speed than the one adopted in its design. Aerodynamic phenomena were known at the time by aeronautical engineers but not by bridge engineers. The bridge was rebuilt with a deep stiffening truss deck in 1950. Many of the existing suspension bridges at the time had been strengthened and all new ones built since the Tacoma Bridge accident have been subjected to detailed aerodynamic studies.

While the US suspension bridge concepts have kept the rigid truss superstructure, the European evolution, mainly due to English engineers, tends towards the use of streamline bridge decks for aerodynamic stability. The Severn Bridge, concluded in 1966, with a main span of 988 m, was the first achievement, eliminating the need to adopt the deep stiffening truss decks. The Tagus River Bridge was opened to traffic in 1966 using a typical rigid truss girder designed by Steinman, New York. The design considered, according to the bid specifications, the possibility of a railroad addition at the lower chord level. With a 1013 m main span, it was, at the time, the longest span in Europe. Thirty years later, the railroad addition was implemented with a completely different concept for this stage than initially foreseen. The trains crossing the bridge nowadays are about 2.5 times heavier than the ones initially foreseen. In the original design, the additional loads due to the railroad were foreseen to be supported by a set stay cables; when the project was implemented, a second cable was added and one new hanger between each of two existing ones was inserted.

In 1981, the Humber Bridge was concluded in the UK. With the longest 1410 m main span at the time, a streamline box girder deck was used as was for the Severn Bridge, but adopting a triangular suspension system for the hangers. It kept the span world record for years until the Great Belt Bridge, 1624 m, and the Akashi Kaikyō, 1991 m, were built in 1998; referred to in Section.

In the second half of the twentieth century, a new generation of cable supported bridges was developed: cable‐stayed bridges. The Strömsund Bridge, concluded in Sweden in 1955, was one of the first cable‐stayed bridges, followed some years later by the three bridges in Dusseldorf, Germany; the North Bridge (260 m span) with two towers and the Knie and Oberkassel Bridges each with a single tower and spans of 320 m and 258 m, respectively [1]. All three Dusseldorf bridges, over the Rhine River, adopted steel decks suspended by stay cables with a harp arrangement and spaced about 30 m at the deck level. Following these bridges, a variety of longitudinal configurations and deck cross sections have been implemented for this bridge typology. However, the most important innovation was the introduction of closed spaced stay cables at the deck level (5–10 m in concrete bridge decks and about 12–20 m in steel decks), allowing the deck to work as a beam on elastic foundations with small bending moments.

At the end of the 1980s in the twentieth century, maximum spans increased, in particular with Annacis Bridge in Vancouver, Canada [10], with a main span of 465 m with a steel‐concrete composite deck. A large step was achieved with the construction of the Normandy Bridge, in France in 1995, following a concept design from Michel Virlogeux [11]. With a main span of 856 m, this bridge adopted a steel box girder deck in the central part (624 m) of the main span continued to the towers and lateral spans with a prestressed concrete box girder deck. The 1000 m span length for cable‐stayed bridges was first reached by two bridges. The first, the Stonecutters’ Bridge concluded in 2009 in Hong Kong, with a 1018 m steel main span, and short 299 m lateral concrete spans [12]. This bridge introduced the option of splitting the deck cross section in to two separate boxes for aerodynamic stability.

The longest span length for cable‐stayed bridges is presently the second, the Russky Bridge, built across the Eastern Bosphorus strait in Vladivostok in 2012, adopting a single box girder deck with a main span of 1104 m and lateral stay cable suspension, as in all other very long cable‐stayed bridges [13].

The increased development of cable supported bridges, either suspension bridges or cable‐stayed bridges, will continue in the coming years. Suspended spans above 3000 m, like the one considered in the design of the Messina Bridge [14], may be achieved in the near future.

Even if span length is often taken as key parameter to evaluate historical bridge evolution, one should take into consideration that many other aspects and solutions had decisive contributions to the development of bridge design throughout history. Even considering only cable supported bridges, a variety of bridge innovative solutions may be referred to as:

• The three‐dimensional arrangement of stay cables – the Lérez River Bridge, Spain [4];
• The multiple cable‐stayed bridges – Millau Viaduct, France [15], and Rion‐Antirion Bridge, Greece [16];
• The combination of suspended and cable‐stayed solutions – the Third Bosphorus Bridge, Turkey [17].¹