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THE USAGE OF BRIDGES

A bridge is designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic. An aqueduct is a bridge that carries water, resembling a viaduct, which is a bridge that connects points of equal height. A road-rail bridge carries both road and rail traffic.

Bridges are subject to unplanned uses as well. The areas underneath some bridges have become makeshift shelters and homes to homeless people, and the undersides of bridges all around the world are spots of prevalent graffiti. Some bridges attract people attempting suicide, and become known as suicide bridges.

To create a beautiful image, some bridges are built much taller than necessary. This type, often found in east-Asian style gardens, is called a ‘Moon bridge’, evoking a rising full moon. Other garden bridges may cross only a dry bed of stream washed pebbles, intended only to convey an impression of a stream. Often in palaces a bridge will be built over an artificial waterway as symbolic of a passage to an important place or state of mind. A set of five bridges cross a sinuous waterway in an important courtyard of the Forbidden City in Beijing, the People's Republic of China. The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants.

Some bridges carry special installations such as the tower of Nový Most bridge in Bratislava which carries a restaurant. Other suspension bridge towers carry transmission antennas. A bridge can carry overhead power lines as does the Storstrøm Bridge. In railway network, an over-bridge is a bridge crossing over the course of the railway. In contrast, an under-bridge allows passage under the line.

 

THE EXAMPLES OF ANCIENT ARCHITECTURAL STRUCTURES

(THE LIST OF ANCIENT ARCHITECTURAL RECORDS)

The list of ancient architectural records consists of record-making architectural achievements of the Greco-Roman world from 800 BC to 600 AD.

Bridges

• The highest bridge over the water or ground was the single-arched Pont d'Apl which carried irrigation water for Aosta across a deep Alpine gorge. The height of its deck over the torrent below measures 66 m.
• The largest pointed arch bridge by span was the Karamagara Bridge in Cappadocia with a clear span of 17 m. Constructed in the 5th or 6th century AD across a tributary of the Euphrates, the now submerged structure is one if the earliest known examples of pointed architecture in late antiquity, and may even be the oldest surviving pointed arch bridge.
• The largest rivers to be spanned by solid bridges were the Danube and the Rhine, the two largest European rivers west of the Eurasian Steppe. The lower Danube was crossed at least at two different crossing points (Drobeta-Turnu Severin, Corabia), while the middle and lower Rhine at four (Mainz, Neuwied, Koblenz, Cologne). For rivers with strong currents and to allow swift army movements, pontoon bridges were also routinely employed. Going from the distinct lack of records of solid bridges spanning larger rivers elsewhere, the Roman feat appears to be unsurpassed anywhere in the world until well into the 19th century.
• The longest bridge, and one of the longest of all time, was Constantine's Bridge with an overall length of 2437 m, 1137 m of which crossed the Danube's riverbed.
• The second longest bridge was the monumental Trajan's Bridge which was situated further upstream from Constantine's. It was a record-holder in various categories, such as the largest bridge by span and the longest segmental arch bridge. Erected 104–105 AD by the engineer Apollodorus of Damascus for facilitating the advance of Roman troops in the Dacian Wars, it featured twenty-one spans covering a total distance of between 1070 and 1100 m. These twenty-one wooden arches spanned 50 m each from centreline to centreline. Its wooden superstructure was supported by twenty concrete piers.
• The longest existing Roman bridge is the sixty-two span Puente Romano at Mèrida, Spain (today 790 m).
• The total length of all aqueduct arch bridges of the Aqua Marcia to Rome, constructed from 144 to 140 BC, amounts to 10 km.
• Pont Serme in southern France reached a length of 1500 m, but may be better classified as an arcaded viaduct.
• The Bridge at Limyra in modern-day Turkey, consisting of twenty-six flat brick arches, features the greatest lengths of all extant masonry structures in this category (360 m).
• The tallest bridge was the Pont du Gard, which carried water across the Gard river to Nоmes, southern France. The 270 m long aqueduct bridge was constructed in three tiers which measure successively 20.5 m, 19.5 m and 7.4 m, adding up to a total height of 47.4 m above the water-level. When crossing deeper valleys, Roman hydraulic engineers, for reasons of relative economics, preferred inverted siphons over bridges; this is evident in the Lyon aqueduct where seven out of nine siphons exceed the 45 m mark, reaching depths up to 123 m. The tallest road bridges were the monumental Alcбntara Bridge, Spain (ca. 42 m), and the bridge at Narni (30 m).

• The widest bridge was the Pergamon Bridge in Pergamon, Turkey. The structure served as a substruction for a large court in front of the Serapis Temple, allowing the waters of the Selinus river to pass unrestricted underneath. Measuring 193 m in width, the dimensions of the extant bridge are such that it is frequently mistaken for a tunnel, although the whole structure was actually erected above ground. A similar design was also executed in the Nysa Bridge which straddled the local stream on a length of 100 m, supporting a forecourt of the city theatre. By comparison, the width of a normal, free standing Roman bridge did not exceed 10 m.

Load capacity plus ratio of clear span against rise, arch rib and pier thickness:

• The bridge with the greatest load capacity – as far as can be determined from the limited research – was the Alcàntara Bridge the largest arch of which can support a load of 52 t, followed by the Ponte de Pedra (30 t), Puente Bibei (24 t) and Puente de Ponte do Lima (24 t) (all in Hispania). According to modern calculations, the Limyra Bridge, Asia Minor, can support a 30 t vehicle on one arch plus a load of 500 kp/mІ on the remaining surface of the arch. The load limit of Roman arch bridges was thus far in excess of the live loads imposed by ancient traffic.
• The bridge with the flattest arches was the Trajan's Bridge, with a span-to-rise ratio of about 7 to 1. It also held several other important architectural records (see below). A number of fully-stone segmental arch bridges, scattered throughout the empire, featured ratios of between 6.4 and 3.0, such as the relatively unknown Bridge at Limyra, the Ponte San Lorenzo and the Alcontar Bridge. By comparison, the Florentine Ponte Vecchio, one of the earliest segmental arch bridges in the Middle Ages, features a ratio of 5.3 to 1.
• The bridge with the most slender arch was the Pont-Saint-Martin in the Alpine Aosta Valley. A favourable ratio of arch rib thickness to span is regarded as the single most important parameter in the design of stone arches. The arch rib of the Pont-Saint-Martin is only 1.03 m thick what translates to a ratio of 1/34 respectively 1/30 depending on whether one assumes 35.64 m or 31.4 m to be the value for its clear span. A statistical analysis of extant Roman bridges shows that ancient bridge builders preferred a ratio for rib thickness to span of 1/10 for smaller bridges, while they reduced this to as low as 1/20 for larger spans in order to relieve the arch from its own weight.
• The bridge with the most slender piers was the three-span Ponte San Lorenzo in Padua, Italy. A favourable ratio between pier thickness and span is considered a particularly important parameter in bridge building, since wide openings reduce stream velocities which tend to undermine the foundations and cause collapse. The approximately 1.70 m thick piers of the Ponte San Lorenzo are as slender as one-eighth of the span. In some Roman bridges, the ratio still reached one-fifth, but a common pier thickness was around one third of the span. Having been completed sometime between 47 and 30 BC, the San Lorenzo Bridge also represents one of the earliest segmental arch bridges in the world with a span to rise ratio of 3.7 to 1.

Columns

List of Roman victory columns

• The tallest Corinthian columns, a style which was particularly popular in Roman monumental construction, adorned the Temple of Jupiter at Baalbek, reaching a height of 19.82 m including base and capital; their shafts measure 16.64 m high. The next two tallest are those of the Temple of Mars Ultor in Rome and of the Athenian Olympieion which are 17.74 m (14.76 m) respectively 16.83 m (14.00 m) high. These are followed by a group of three virtually identical high Corinthian orders in Rome: the Hadrianeum, the Temple of Apollo Sosianus and the Temple of Castor and Pollux, all of which are in the order of 14.80 m (12.40 m) height. All these colonnades, though, are eclipsed by the single Pompey's Pillar which is 26.85 m high with its base and capital (20.46 m without).
• The tallest victory column was the Column of Marcus Aurelius, Rome, with the height of its top above ground being 39.72 m. It thus exceeds its model, Trajan's Column, by 4.65 m, chiefly due to its higher pedestal. In antiquity, the imperial capitals of Rome and Constantinople saw the erection of many more triumphal columns, some of which, like the demolished Column of Justinian, may well have exceeded these heights.

Dams

• The dam at Cornalvo, Spain, is one of the tallest Roman dams still in use (28 m).
• The largest arch dam was the Glanum Dam in the French Provence. Since its remains were almost completely obliterated by a 19th century dam on the same spot, its reconstruction relies on prior documentation, according to which the Roman dam was 12 m high, 3.9 m wide and 18 m long at the crest. Being the earliest known arch dam, it remained unique in antiquity and beyond (aside from the Dara Dam whose dimensions are unknown).
• The largest arch-gravity dam was the Kasserine Dam in Tunisia, arguably the biggest Roman dam in North Africa with 150 m length by 10 m height by 7.3 m width. However, despite its curved nature, it is uncertain whether the 2nd century AD dam structurally acted by arching action and not solely by its sheer weight; in this case it would be classified as a gravity dam and considerably smaller structures in Turkey or the Spanish Puy Foradado Dam would move up in this category.
• The largest bridge dam was the Band-e Kaisar which was erected by a Roman workforce on Sassanid territory in the 3rd century AD. The approximately 500 m long structure, a novel combination of overflow dam and arcaded bridge, crossed Iran's most effluent river on more than forty arches. The most eastern Roman civil engineering structure ever built, its dual-purpose design exerted a profound influence on Iranian dam building.
• The largest multiple arch buttress dam was the Esparragalejo Dam in Spain, whose 320 m long wall was supported on its air face by buttresses and concave-shaped arches. Dated to the 1st century AD, the structure represents the first and, as it appears, only known dam of its type in ancient times, although portions of the Portuguese Muro Dam were similarly shaped.
• The longest buttress dam was the 632+ m long Consuegra Dam (3rd–4th century AD) in central Spain which is still fairly well preserved. Instead of an earth embankment, its only 1.3 m thick retaining wall was supported on the downstream side by buttresses in regular intervals of 5 to 10 m. In Spain, a large number of ancient buttress dams are concentrated, representing nearly one-third of the total found there.
• The longest gravity dam, and longest dam overall, impounds the Lake of Homs in Syria. Built in 284 AD by emperor Diocletian for irrigation, the 2000 m long and 7 m high masonry dam consists of a concrete core protected by basalt ashlar. The lake, 6 miles long by 2.5 miles wide, is the biggest Roman reservoir in the Near East and possibly the largest artificial lake constructed up to that time. Enlarged in the 1930s, it is still a landmark of Homs which it continues to supply with water. Further notable dams in this category include the little-studied 900 m long Wadi Caam II dam at Leptis Magna and the Spanish dams at Alcantarilla and at Consuegra.
• The tallest dam belonged to the Subiaco Dams at the central Italian town of the same name. Constructed by Nero (54–68 AD) as an adjunct to his villa on the Aniene river, the three reservoirs were highly unusual in their time for serving recreational rather than utilitarian purposes. The biggest dam of the group is estimated to have reached a height of 50 m. It remained unsurpassed in the world until its accidental destruction in 1305 by two monks who fatally removed cover stones from the top. Also quite tall structures were Almonacid de la Cuba Dam (34 m), Cornalvo Dam (28 m) and Proserpina Dam (21.6 m), all of which are located in Spain and still of substantially Roman fabric.

Domes

• The largest dome in the world for more than 1700 years was the Pantheon in Rome. Its concrete dome spans an interior space of 43.45 m, which corresponds exactly to its height from floor to top. Its apex concludes with a 8.95 m wide oculus. The structure remained unsurpassed until 1881 and stills holds the title of the largest unreinforced solid concrete dome in the world. The Pantheon has exercised an immense influence on Western dome construction to this day.
• The largest dome out of clay hollowware ever constructed is the Caldarium of the Baths of Caracalla in Rome. The now ruined dome, completed in 216 AD, had an inner diameter of 35.08 m. For reduction of weight its shell was constructed of amphora joined together, a quite new method then which could do without time-consuming wooden centring.
• The largest half-domes were found in the Baths of Trajan in Rome, completed in 109 AD.
• The largest stone dome was the Western Thermae in Gerasa, Jordan, constructed around 150/175 AD. The 15m wide dome of the bath complex was also one of the earliest of its kind with a square ground plan.