The Bridges of the Future or the Future of Bridges?

Infrastructures are a key factor for economy. Among them, transportation infrastructures are vital for human life and economy. And within the transportation networks, bridges are key elements for connecting people anddelivering goods. For this reason, bridges have been built sincemany centuries ago, in some way, and the advances (and sometimes geographical expansions!!) of ancient cultures all over the world have been related to their ability of constructing permanent bridges. The most representative of this could be the Roman Empire. After many centuries of bridge construction, nowadays we face a long history of experiences that allow us to look to the evolution of bridge engineering along years and, based on that, to try to extrapolate what is the most feasible to come in the next future. The evolution in bridge engineering has been strongly linked to the key advances in the following areas:materials, construction processes, andmodeling. Construction techniques and bridge typologies at the beginning were governed by the mechanical properties and performance of available materials at that time. In fact, when the available materials were stone and masonry (materials that work well in compression but not in tension), the characteristic bridge type was the arch and the construction process, the scaffolding of the complete structure, because the arch action needs the complete structure to develop. For centuries, the arch was the only available bridge type regarding permanent bridges. Of course, suspension and beam configurations were also available but normally with temporary use due to the durability limitations of materials working in tension (vegetal fibers) and bending (timber). Only the appearance in the nineteenth century of new materials as iron and steel, with the ability to resist tensile stresses allowed the birth of permanent suspension and girder bridges. Later on, the combination of a new material, concrete (similar to an artificial stone) and steel, forming reinforced and prestressed concrete made possible for the “new stone” to resist tensile actions and to join segments between them. Something that was not possible with the “old stone”!!. This resulted on an important revolution in the world of bridges. In fact, segmental bridge construction was born, linked to it, and a new group of construction techniques for concrete bridges: balanced cantilever, incremental launching, span-by-span. These new construction processes were also rapidly adopted by the steel bridges. Finally, already in the twentieth century, the use of the computer made affordable the accurate calculation and, therefore, the design and construction of highly redundant bridge types as cable-stayed bridges, and to model very complicate construction sequences. Since then, it seems like bridge engineering related to design and construction of bridges had reached a stationary point and no further relevant advances were envisaged. Bridge history shows us that for any substantial revolution (or let us say a “before” and an “after”) in the field, some relevant fact should occur. There has been a “before” and an “after” in bridge design and construction regarding the come into scene of concrete and steel. Since then, new materials have not appeared. Only recently, fiber reinforced plastics (FRP) were translated into bridge engineering from the aeronautical field. However, these new materials did not lead to relevant changes in bridge typologies or bridge construction schemes, being its main feature, their durability and high strength to weight ratio. There has been also a “before” and an “after” in-bridge construction since the appearance of prestressing. And, finally, there has been