1. Building an arch bridge is not easy because the structure is completely unstable until the two spans meet in the middle. For years, engineers used a technique called centering. In centering, a wooden form supported both spans until they locked together at the top. A newer method supports the spans using cables anchored to the ground on either side of the bridge.
2. Arch bridges are one of the most popular types of bridges, which came into use over 3000 years ago. Because of their design, stone and wood arch bridges became very popular during the Roman Empire, when architects managed to build over 1000 stone arch bridges in Europe, Asia and North Africa. Many of those bridges remain standing even today. Roman designs were usually made with semicircular arches, although several segmented arch bridges were made during their reign. These segmental arch bridges had one crucial design advantage which separated them from ordinary semicircular bridges – they enabled bridge builders to more arch of the bridge much higher and lower the mass of the entire structure. These changes enabled bridges to much easier survive stresses of floods and strong rivers. During the life of Roman Empire, many wondrous bridges, lengthy aqueducts with multiple arches, and bridges with flood openings on the piers were built. As centuries went on, medieval architects improved the designs of Romans, creating arch bridges with narrower piers, thinner arch barrels, lower span-rise rations. Renaissance architects infused into arch bridges not only sound engineering, but also fashion of their time, creating some of the most beautiful and famous bridges of the modern human civilization. In the last 150 years, iron, steel and concrete enabled creation of much more ambitious arch bridges which can now be seen in every country in the world.
3. The basic principle of an arch bridge is its curved design, which does not push load forces straight down. Instead, they are conveyed along the curve of the arch to the supports on each end. These supports (called abutments) carry the load of entire bridge and are responsible for holding the arch in the precise position unmoving position.
4. Tensional force in arch bridges is virtually negligible. The natural curve of the arch and its ability to dissipate the force outward greatly reduces the effects of tension on the underside of the arch.
5. The arch bridge carries loads primarily by compression, which exerts on the foundation both vertical and horizontal forces. Arch foundations must therefore prevent both vertical settling and horizontal sliding. In spite of the more complicated foundation design, the structure itself normally requires less material than a beam bridge of the same span.
Photo Credit: Robert Montgomery https://flic.kr/p/hKofpC