7/15/2008

Bridges Types (3) : Arch Bridge


An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. A viaduct (a long bridge) may be made from a series of arches, although other more economical structures are typically used today.



Possibly the oldest existing arch bridge is the Mycenaean Arkadiko bridge in Greece from about 1300 BC. The stone corbel arch bridge is still used by the local populace. Although true arches were already known by the Etruscans and ancient Greeks, the Romans were - as with the vault and the dome - the first to fully realize the potential of arches for bridge construction.

The engineer Colin O'Connor lists 330 Roman stone bridges for traffic, 34 timber bridges and 54 aequeduct bridges, a substantial part still standing and even used to carry vehicles.

In more modern times, stone and brick arches continued to be built by many civil engineers, including Thomas Telford, Isambard Kingdom Brunel and John Rennie. A key pioneer was Jean-Rodolphe Perronet, who used much narrower piers, revised calculation methods and exceptionally low span-to-rise ratios. Different materials, such as cast iron, steel and concrete have been increasingly used in the construction of arch bridges.

Although rarely built, the Romans also introduced segmental arch bridges into bridge construction. The 330 m long Limyra bridge in southwestern Turkey features 26 segmental arches with an average span-to-rise ratio of 5.3:1, giving the bridge an unusually flat profile unsurpassed for more than a millennium. Trajan's bridge over the Danube featured open-spandrel segmental arches made of wood (standing on 40 m high concrete piers). This was to be the longest arch bridge for a thousand years both in terms of overall and individual span length.

Roman bridges featured from an early time onwards flood openings in the piers, e.g. in the Pons Fabricius in Rome (62 BC), one of the world's oldest major bridges still standing.


In China, the oldest existing bridge is the Zhaozhou Bridge of 605 AD (although bridges were built since the ancient Zhou Dynasty), which combined a very low span-to-rise ratio of 5.2:1, with the use of spandrel arches (buttressed with iron brackets). The Zhaozhou Bridge is the world's first wholly-stone open-spandrel segmental arch bridge.

Source : wikipedia

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