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THE EVOLUTION OF COMPOSITE BRIDGES

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Throughout history, the discovery and use of new construction materials enabled the evolution of the different structural typologies. Bridges are not indifferent to his phenomenon. In fact, current bridges are the result of the evolution over the years. From antique times until well into the 19th century, the stone arch-bridge cohabited with the wooden bridge, being the first one the structural typology willing to endure over time. However, its hegemony as the only way to build long lasting bridges will end with the emergence of cast iron, wrought iron and finally steel. Likewise, mass concrete and later steel embedded in concrete (known as reinforced concrete) will open up new typological and formal possibilities.

It is in the early 20th century when the composite bridge of concrete and steel appears. This is a new form of collaboration between materials, not mixing them as in reinforced concrete, but connecting them to work together. This working method is the logical consequence of their optimized use, both on the resistance side and the construction side. However, the composite bridge doesn’t appear as a solution for resistance or construction, but as an answer to the need of easy to maintain and stiff rolling platforms for metal bridges, which so far had wooden decks. It was in the early 1920s, after tests carried out at Skunk River Bridge (Iowa), when it became clear the joint work between concrete and steel, despite this bridge was not initially designed as a composite bridge. Finally, it is from 1930 on when the composite section extends to the constructions of that period.

In Spain, this new typology will not be introduced until the end of the Civil War. Eduardo Torroja bring innovative ideas for the proposed composite section, as harnessing the self-supporting capacity of the steel part, the concreting in successive stages, and introducing the arc welding, which enabled to make compact junctions suitable to be placed inside the concrete. To solve the load transfer, he suggests metal plates with hooks inside the concrete. Furthermore, he proposes the double composite action in negative bending moment areas (supports), a significant breakthrough for future bridge constructions. Notwithstanding the above, in Spain the construction of bridges after the Civil War was determined by the almost exclusively use of concrete.

The beginning of the modern composite bridges is set on the 1950s, on the basis of the innovative contributions of the German technology. The most noteworthy of these are the widespread use of welds (instead of bolt connectors, rivets or screws) and the use of laminated plates, as a result of the improvement of quality and advances in manufacturing processes, as well as a better knowledge of the behavior of thin-walled metallic structures. The other major change is the shift from statically determinate (isostatic) to indeterminate (hyperstatic) solutions for the deck of the bridge. Perhaps the determining factor in the development of composite bridges is the great progress from the analytical point of view, establishing a theoretical basis as a result of the work of Konrad Seattle, based on the works of Franz Dischinger about the concrete rheological effects.

Specifically in Spain, Julio Martínez Calzón and José Antonio Fernández Ordoñez are leading figures for their technical and construction innovations such as the use of different materials, the application of white concrete and self corrosion-resistant steels, the use of complete precast planks and preconnection prestressing between them to guarantee the deck’s continuity. These can be observed on Juan Bravo Bridge (1970) over Paseo de la Castellana, in Madrid, with a central continuous section of three spans of 29-38-29 metres. Taking into account these new contributions, a new composite bridge trend is developed, marked by the use of composite frames, the improvement in the building process considering stress evolution, the use of double composite action on the supports, and the application of precast planks and semi-resistant planks, among others. The first construction of this type was El Diablo Bridge (1972) over Llobregat River, in Martorell (Barcelona), with a middle span of 100 metres.

FOTO 1

Figure 1. Juan Bravo Bridge (1970) over Paseo de la Castellana

FOTO 2

Figure 2. El Diablo Bridge (1972) over Llobregat River, in Martorell (Barcelona)

Over the years, new typologies and construction techniques appeared, which were more favourable for composite structures, and gradually both reinforced and prestressed concrete hegemony disappear on the new built bridges. The great thrust of civil engineering in our country due to Barcelona Olympic Games and Seville Expo, created the conditions for the generalization of composite structures. In addition, during the last decade our country has designed and built a significant number of exceptional composite bridges of diverse typology.

Nowadays, composite bridges are a real competitive alternative to concrete bridges. Their concept is characterized by the optimal use of the materials, where concrete is kept under compression and structural steel works under tensile stress, the close relationship with the construction process, and the formal possibilities that this typology enables.

Bibliography:

“Puentes, estructuras, actitudes”. Julio Martínez Calzón

“Evolución tipológica y estética de los puentes mixtos en Europa”.  Jorge Bernabéu Larena

“Construir en acero los puentes de luces medias” Francisco Millanes Mato

Gambí Romero, María

Grandal Vivero, Celia

Lumbreras de la Fuente, Valentina

Montero Pérez, Antonio

Universidad Politécnica de Madrid

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