Special Bridges

Suspension bridges are used for the biggest span widths. The economic application area applies to span widths between 300m and 1500m. In some cases, smaller bridges with span widths of approx. 100m can be constructed.

The structure consists of two supporting towers with main carrying cables attached on both sides. Extremely solid connection cables are mounted on the carrying cables and these hold the deck and the underlying main supports. Tensile forces act on the cables, which must not only absorb the entire traffic and intrinsic loads of the supporting structure, but also the dynamic wind load, which is particularly relevant for suspension bridges. The pressure loads produced in this way are dissipated via the towers into the foundations.

Span width: 100m – 2000m
Deck width: up to 36m

Cable-stayed bridges consist of a long main support which is suspended from a tower with inclined reinforcing cables. The average span width of cable-stayed bridges is generally between 100m and 400m, but can in special cases be up to 500m.

The method used to fasten the inclined cables to the top of the tower comes from suspension bridge engineering, where the inclined cables lie in a tower saddle (fan-shaped arrangement), so that each of the inclined cables anchored in the main span runs over the tower and is then anchored in the following span. Alternatively, inclined cables can also be fastened across the height of the tower so that the cables run parallel to each other (harp-shaped arrangement).

As with suspension bridges, guarding against wind-based vibration is extremely important. A stable structure can be achieved by an aerodynamically favourable design of the bridge cross-section and the cables.

The towers can be designed in numerous ways (e.g. A-towers, Y-towers, central tower, two towers), depending on the foundation characteristics.

Span width: 100 – 500m
Deck width: up to 36m

Plate-girder and box-girder bridges from Waagner-Biro can be used flexibly as they adapt to numerous span widths and shapes. They offer economic solutions for compound structures, where a steel girder sheath is combined with a reinforced steel deck. In plate-girder bridges, the flanges are welded to the web plates. In box-girders, the strut panels forming the box girder floor replace the bottom flanges.  Steel bridge support structures are frequently designed as orthotropic deck panels, i.e. the deck rests on longitudinal girders or trapezoidal ribs and transverse girders.

Steel bridges with double or multiple web plate girders or sheet steel girders are used for span widths of up to approx. 250m. Girders with variable flange heights ("coved girders") are usual for span widths over 100m.

Particularly economic solutions are possible with compound structures where the deck panel is made of reinforced concrete (eventually pre-tensioned). These concrete panels are connected to the steel main girder using connecting dowels so that a unified support structure is created, combining the advantages of the concrete (price-effective deck) with the advantages of the steel (good controllability, durability and reinforcement ability).  This solution is used both for full plate girders and for box girders.

Span width: 30 – 250m
Deck width: up to 36m

Arched bridges are characterised by their elegant shape and visible support function. Depending on the requirements of the location, the deck can be suspended on hangers or positioned on supporting columns over the arches. The arch bridge already played an important role in the pioneering years of Waagner-Biro. Depending on the surrounding land, bridges are built with arches above the deck ("suspended deck") or with arches where the deck is above the arches and supported by them ("standing deck").

Arched bridges are economic in span widths from 100m to 300m (e.g. the Trisanna Bridge in Tirol, the arched bridge for the St. Pölten freight train bypass in Lower Austria), but smaller structures can also be created (e.g. city park bridge, footbridge) in special cases.

Span width: 80 – 300m
Deck width: up to 36m

Bridges whose main supports are formed as truss girder structures have the advantage of relatively lower weights for both the overall structure and the individual components (truss beams). Waagner Biro has extensive experience in such constructions. These bridges are built for span widths of up to 250m and can be used for roads, railways and other purposes.

Truss girder bridges can be bolted together or fully welded. Waagner-Biro has long experience of trough truss girder bridges (truss girders on both sides above the deck) and suspended truss girders (deck on upper flange, truss girders below the deck).

Span width: 80 – 300m
Deck width: up to 36m

Pipeline bridges, in the form of suspension bridges, are used when oil and gas lines, conveying belts, water pipes and drainage channels have to pass over large rivers or valleys. Waagner-Biro already developed in the 60's a unique supporting system for improved stabilisation of pipe bridges using Y-shaped towers with three cables spatially inclined to each other.

The system is characterised by two inclined – V-shape arranged - support walls, supplemented by an upwardly arched central pre-stressed cable running along the pipe line. An important element of the structure is the central node. It connects the support and pre-stressed cables in the centre of the bridge and therefore contributes greatly to the deformation stiffness under fractional loads – normally a weak point in such suspension bridge systems. This structure is therefore also suitable for pedestrian traffic.

The slim and yet compact appearance of the support structure is characterised by the two Y-towers. Many such support structures with span widths over 300 m have been built by Waagner-Biro.

Span width: 100 – 500 m