There are several ways to create a bridge, either for pedestrians, vehicles, or trains. PFEIFER Structures specializes in three types of bridges: cable-stayed bridges, suspension bridges, and tied arch bridges. All three types of bridges are based on steel structure(s) and cables. However, there are significant differences in how the bridge bears the load, how much material is used, how the steel structures and cables are connected, and the bridge’s aesthetic.
Cable-stayed bridges are differentiated from other bridge structures by how the cables connect directly from the bridge deck to towers or pillars. Cables and tension rod systems will connect from the bridge to the towers or pillars directly, with the towers or pillars bearing the structure’s load. Cables use tension to help keep the bridge deck stable and in place. Croatian-Venetian inventor Fausto Veranzio first designed Cable-stayed bridges in 1595. The earliest cable-stayed bridge built was the Dryburgh Abbey Bridge in Scotland, built in 1817.
- Advantages of a Cable-Stayed Bridge
- Faster construction time compared to other bridge types.
- More rigid than suspension bridges.
- Flexible design.
- Disadvantages of a Cable-Stayed Bridge
- Only suitable for short to medium distances (Shorter span than suspension bridges).
- Cables can be prone to corrosion and high levels of fatigue.
- Not suitable for extreme climate conditions or earthquake-prone areas.
Suspension bridges are differentiated from other bridge structures by how the cables vertical suspender cables, which then connect to the towers or pillars. A vertical suspender cable(s) will connect to the towers or pillars and to the ground, bearing the load of the structure. Cables and tension rod systems will then connect from the load-bearing cable(s) to the bridge deck. Tibetan bridge-builder Thangtong Gyalpo first designed the suspension bridge in the 1400s. Gyalpo built the first suspension bridges in 1433.
- Advantages of a Suspension Bridge
- Best bridge type for creating the longest spans with minimum piers.
- Regarded by many as aesthetically pleasing – suspension bridges are amongst the most famous landmarks of New York City and London, two cities with many iconic landmarks.
- Waterway or roadway beneath the bridge can be left open while the bridge is under construction.
- The design allows for deck sections to be replaced.
- Disadvantages of a Suspension Bridge
- A combination of vertical pressures and extreme side wind speeds can lead to a failure of the span.
- High winds can cause a suspension bridge to start vibrating.
- They can struggle to support focused heavy weights (e.g., trains).
- Some suspension bridges require extensive foundation work if the ground is soft.
Tied Arch Bridges
Tied arch bridges are differentiated from other bridge structures by the arch(es) that spans over the bridge. Cable and tension rod systems connect the bridge deck to the arch(es). Tied arch bridges use the tension of their vertical cables, together with the compression of the arch, to support the load and keep the bridge stable. The downward pressure from the arch structure to the bridge’s deck is translated into tension by the vertical ties. The first tied arch bridge was the Windsor Railway Bridge in Windsor, England, in 1849.
- Advantages of a Tied-Arch Bridge
- Very strong.
- Less force on abutments.
- It can be built off-site and transported into place.
- Disadvantages of a Tied-Arch Bridge
- Regular maintenance is required to ensure the stability of the hangers and arch.
- The size of each span is limited as compared with suspension bridges
- Arches are typically more expensive to build than towers or pillars of other types of bridges of the same length.