ARCH BRIDGES

Arch Bridge – Types of Arch Bridges

Arch bridge is one of the most popular types of bridges, which came into use over 3000 years ago and remained in height of popularity until industrial revolution and invention of advanced materials enabled architect to create other modern bridge designs. However, even today arc bridges remain in use, and with the help of modern materials, their arches can be build on much larger scales.

The basic principle of arch bridge is its curved design, which does not push load forces straight down, but 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. Conveying of forces across the arch is done via central keystone on the top of the arch. Its weight pushes the surrounding rocks down and outward, making entire structure very rigid and strong.

Because of this design, stone and wood arch bridges become very popular during the Roman Empire, whose architects managed to build over 1000 stone arch bridges in Europe, Asia and North Africa. Many of those bridges remain standing even today, giving us the chance to personally see the wonders of the ancient architecture. 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, they built many wondrous bridges, lengthy aqueducts with multiple arches, bridges with flood openings on the piers, and many others.

As centuries went on, medieval architects improved the designs of Romans, creating arch bridges with narrower piers, thinner arch barrels, lower span-rise rations, pointed arches, and increased spans of arches (increasing to over 70 meters, most famously on the bridge at Trezzo sull’Adda who was in use from 17th to the end of 18th century). 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 (such as Rialto Bridge in Venice). 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.

Types of Arch Bridges

• Corbel arch bridge – Even though Corbel arch does not function in the same way as true arch bridges (they are not conveying forces across the arch), they can be created to look very similar like them. They are made by laying successive layers of masonry or stone with each having successfully larger cantilevers.
• Aqueducts and canal viaducts – To bridge large distances, ancient romans built series of supports which were connected with stone arches. These series of arched structures were butt not only in one layer like ordinary bridge, but with several layers that could reach very impressive heights.
• Deck arch bridge – Common arch bridge in which deck is situated on top of the arch.
• Through arch bridge – Arch Bridge in which deck is not situated completely above the arch, but it travels in one part below it and is suspended to it via cables or tie bards. Famous Sydney Harbour Bridge is the best example of this design.
• Tied arch bridge – Also known as bowstring arch bridge, it incorporates a tie between two opposite ends of the arch.

Tied-arch Bridge Facts,

History and Examples

Tied-arch bridge (also called bowstring-arch or bowstring-girder bridge) is a type of bridge that has an arch rib on each side of the roadway (deck), and one tie beam on each arches, that support deck. Vertical ties connected to the arches support deck from above. It can be considered a bridge between arch bridge and a suspension bridge. They work like arch bridges on one hand, because force of the load on the deck (thrust) is translated as tension to the curved top chord by vertical ties of the deck which try to flatten the arch and to push its tips outward into the abutments. Tips of the arch of this bridge are tied together by a bottom chord. This allows the bridge to be constructed with less robust foundations because force on the abutments is low. Tied-arch bridges can be built on elevated piers or in areas of unstable soil. One more positive attribute of this type of bridge is that it does not depend on horizontal compression forces for its integrity which allows them to be built off-site and then transported into place. But tied-arch bridges are not perfect. They can have poor welds at the connection between the arch rib and the tie girders, and at the connection between the arch and vertical ties. These welds, after some time have to be repaired which is costly, time-consuming and an inconvenience. Construction and design of this bridge is non-redundant which means that if even one of the two tie girders fails the whole structure will collapse without anything to work as safety. As a last problem, tied arch bridges are more expensive to build compared to the other types of bridges of the same length.

Some examples of the tied-arch bridges are:

• The Lowry Avenue Bridge built in 2012 that crosses Mississippi River in Minneapolis, Minnesota. It has 480 m in length and its longest span 137 m. It carries road traffic.
• The Daniel Hoan Memorial Bridge , which was finished in 1977. It spans Milwaukee River in Milwaukee, Wisconsin. It carries road traffic over its length of 3,057.8 m and six lanes.
• The Fort Pitt Bridge was opened in 1959. Its overall length is 368 m while its longest span has 230 m. It was the world’s first computer designed tied-arch bridge and the first double-decked tied-arch bridge.
• The Blackfriars Street Bridge in London, Ontario, Canada was finished in 1875. It still carries motor and pedestrian traffic. Its length is 65.8 m.
• Windsor Railway Bridge in Windsor, Berkshire, England was finished in 1849. It was designed by Isambard Kingdom Brunel. It has three bowstring trusses which create two bays for railway tracks and it is the World’s oldest wrought iron railway bridge still in regular service.
• The Godavari Arch Bridge over the Godavari River in Rajahmundry, India. It was built in 1997 and its total length is 2,745 m. Its longest span has 97.5 m. Bridge carries railway, namely South Central Railway Line of India and can carry trains that go as fast as 250 km/h.
• Lake Champlain Bridge over the Lake Champlain between Crown Point, New York and Chimney Point, Vermont has 670 m of total length and a longest span of 150 m. It was finished in 2011. It carries road traffic.
• GFRP Lleida Pedestrian Bridge in Leida, Spain spans Madrid-Barcelona high-speed rail link. It was built in only three months and was finished in October 2001. Its total length is 38 m.
• The John McLoughlin Bridge spans the Clackamas River between Oregon City and Gladstone, Oregon, United States. Its total length is 219.5 m and it carries four lanes of Oregon Route 99E.