BRIDGES ON THE DANUBE - Introductory Report - Prof. Dr. Miklós Iványi

The river Danube is a unique international waterway flowing 2857 km across Europe. It flows from the heights of the Schwarzwald Massif down to its estuary in the Black Sea delta. In its passage, the river crosses 22 geographical longitudes joining 8 countries: Germany, Austria, Slovakia, Hungary, Yugoslavia, Romania, Bulgaria and Ukraine.

It is largely these factors, together with the importance of the management of its water resources, which historically encouraged civilisations and cultures to develop along the banks of the river.

The River Danube drainage basin includes glacier-covered mountains, mid-mountain chains clad with forests, karst formations devoid of growth, highlands and uplands, table lands, plateaus with deeply carved river valleys, and wide plains and depressions.

The Danube with a total length of 2857 km is listed immediately after the river Volga (length 3740 km), as the second biggest river in Europe. In terms of length it is listed as the 21st biggest river in the world, in terms of drainage area it ranks as 25th with a drainage area of 817000 square km.

The Danube basin extends in a westerly direction from the Black Sea into central and southern Europe. The maximum length of the river basin is 1630 km.

Twelve countries share the Danube catchments, though more than 70 % of the catchment lies within four countries. The smallest, almost insignificant parts of the catchment area are in Switzerland, Albania, Italy and Poland.

The sources of the Danube tributaries adjoin the source of the Rhine tributaries in the west and Northwest, the Weser, Labe, Odra and Visla river basins in the north, the Dnester river basin in the Northeast and the basin of the rivers flowing into the Adriatic and Aegean Sea in the south.

The rich, fertile riparian Danube territories attracted the interest of nations pursuing trade, as well as conquerors and nomads since earliest times. Early in the 8th to 7th century B. C. Phoenicians, Egyptians, and Greeks penetrated the Danube estuary, entering into trade contacts with the local population.

In the 6th century B. C. Persian Monarch Darius the First had tried to occupy the territories adjacent to the lower Danube basin, as did Alexander the Macedonian in 334 B. C. In the first century A. D. the upper Danube formed a part of the Roman Empire. In the years 101-106 the Roman Emperor Traianus defeated the Dacian tribes settled in the lower Danube basin. He had built the Traian's Bridge across the Danube at Turnu Severin in the Iron Gate Gorge, and on the right bank he constructed the Traian's Road, the existence of which is documented by the Tabula Traiana.

To investigate the origin of the name "Donau" (Danube) one has to go back to the Celtic tribes who lived in the upper Danube basin. The word "Danu" is of Celtic origin and signifies "swift, rapid, violent, undisciplined". Emperor Caesar in his work "De Bello Gallico" had named the stream Danubius. Phoenicians and Greeks had explored the river from the estuary upstream but knew only the lower course, known as Istros or Ister.

The name Danubius can be found in the works of Aristoteles, Ovid, Strabo, Pliny the Elder. "Istros" is mentioned in works by Herodotus and Virgil, when referring to the lower Danube, and Histerus is mentioned by Cicero. Other nations migrating along the stream called the river Donau, Dunaj, Duna, Dunav, Dunarea, the name being transformed and modified according to the language of the people.

In the age of the Roman Empire the Danube had an important strategic significance and this had persisted to the present time. Considerable migration of nations took place along the Danube, including the crusaders, and later the river became a strategic waterway and an artery of life influencing the development of European history. At the same time the economic significance of this mighty river had been growing.

The main function of a bridge is to carry traffic over a crossing, which may be a river, a canyon, or another line of traffic. Besides serving its specific purpose safely and economically, a bridge should be designed aesthetically so that to will fit into and often enhance the beauty of its surroundings.

A good bridge layout must take into consideration the geographical and geological conditions of the site. Clearance requirements, erection procedures, and the method of foundation construction will affect the type and span of the superstructure. The designer should consider all these factors during analysis and detailing.

Of the thousands of bridges existing throughout the world, no two bridges are identical. They differ at least in some details. However, they may be classified into a number of main types.

Bridges can be classified either according to the service they perform or according to the structural arrangement they possess. The majority of bridges are either highway or railway bridges. There are also bridges carrying a combination of traffic, such as a highway bridge with streetcars or pedestrian sidewalks, or a railway bridge carrying highway traffic at the same time. Occasionally there are bridges for pedestrians only, or bridges carrying canals and pipelines. Some bridges are moveable, they can be opened either vertically or horizontally so, as to permit river traffic to pass under them.

Classified according to the cross section of the bridge, a deck bridge is one that has its floor resisting on top of all the main load carrying members, so that there is no bracing over the top of the traffic. If the floor is connected to the lower portion of the main load carrying members so that the bracing goes over the traffic, it is called a through bridge. If there is no overhead bracing but the main load carrying members project above the floor level, it is called a semi-through or a pony truss bridge. A double-deck bridge is one, in which there are decks on two different levels, both of which can be through decks, or one can be a through and the other an open deck. For economy in bracing, either the deck or the through type may have a triangular section where the roadway is supported by two inclined frames.

Classified according to the make-up of the main load carrying members, an I-beam bridge has rolled I beams as the main load carrying members. When spans exceed a certain limit, built-up plate girders are used and they are known as plate girder bridges. For still longer spans, truss bridges are usually more economical. Occasionally, the Vierendeel truss with quadrangular framing instead of the usual triangular framing is used. For very long spans, the suspension bridge is found to be economical, with high-tensile-strength steel cables carrying the main loads. Suspension bridges are usually stiffened with girders to obtain rigidity. In all these cases, the number of trusses or cables may vary from two to three or more, depending on the economy of layout. Single truss bridges have been occasionally advocated, though seldom built as yet.

Classified according or the structural layout of the main load carrying members, most of truss, girder, and beam bridges can have the following various arrangements. One common arrangement is the simple span type where the main carrying members span from one support to another, but are discontinuous over the piers. It is sometimes economical to make the spans continuous, so as to reduce the maximum positive moments. Such a layout is slightly more difficult to analyse and may be objectionable if the foundations are likely to settle unevenly, thus producing settlement stresses in the members. Some engineers prefer the cantilever layout to the continuous, possessing favourable moments along its length but not subject to settlement stresses and also easier to analyse. However, a cantilever layout requires special hinge arrangements and is less rigid that a continuous one. Besides, the continuous layout has a higher ultimate load carrying capacity, as indicated by the theory of limit design.

The arch layout is considered to be more aesthetic than the simple spans. The arch itself can be made of girders or trusses as may suit the case.

The most common design is to provide two hinges, one at each support - rendering the arch stresses statically indeterminate to the first degree. But the three-hinge, one-hinge, and hingeless types are sometimes employed. The horizontal component of the arch reaction force may be resisted by the abutments and piers, or by ties along the roadway.

Classified according to the type of connections, the great majority of steel bridges are riveted, although welded and bolted bridges are being designed and constructed more and more.

Taking into account the classification categories mentioned above, the structural system of the main girders of the Danube bridges was summarised in tables, including the traffic conditions as well.

The following categories were drawn in tables:

Truss Girder,
steel Railway Bridges
Highway Bridges
Railway and Highway Bridges
Plate Girder Bridges (steel)
Box Girder Bridges (steel)
Reinforced Concrete Bridges
Arch Bridges
Cable Stayed Bridges (steel, reinforced concrete)
Chain Suspension Bridges
Cable Suspension Bridges Highway Bridges
Pipeline Bridges

The tables do not contain those bridges which are:

· parts of hydropower or navigation systems or dams: YU-R/1 Iron Gate II, YU-R/3 Iron Gate I, A/17 Ybbs-Persenbeug, D/19 Straubing,

· demolished or destroyed ones: YU-R/2 Traian's Bridge, H/9 Kossuth bridge, H-SK/1 Esztergom-Sturovo, "Mária Valéria" bridge),

· the only stone Danube bridge from the Middle Ages: D/27 Regensburg, "Steinerne" bridge.

Tables