What are Cable-Stayed Bridges?
By Ileana Garnand, Digital Editor
You do not have to be an engineer to be interested in and appreciate the beauty of bridges, especially if you travel across one regularly. There are various types of bridge designs used around the world today, but the cable-stayed bridge has become one of the top choices for structures carrying traffic.
Chances are, you have seen at least a photo of one. Here is a rundown of how cable-stayed bridges work and why they may be preferred over other designs.
What is a Cable-Stayed Bridge?
A cable-stayed bridge is a structural system with a bridge deck supported by stay cables directly attached to towers. It can carry cars, trucks, light rail, cyclists and pedestrians.
Individual cable-stayed bridges may vary in certain designs, including how many cables and towers are used and where they are placed. The cables typically form a fan-like pattern or a series of parallel lines.
They are the preferred choice for a bridge span of approximately 500 to 2,000 feet. At this range, the structures are highly economical and often visually elegant.
Cable-stayed bridges can be longer than cantilever bridges, truss bridges, arch bridges and box girder bridges, but are still typically shorter than suspension bridges.
How Do Cable-Stayed Bridges Work?
The key parts of a cable-stayed bridge use either tension or compression.
The stay cables transfer the structural load to the towers, holding the bridge in place without having to use piers, columns or other supports. The towers then support and transfer the load to the bridge’s foundations.
The entire bridge system is in balance because of compression forces in the towers and deck, paired with tension forces in the stay cables.
How are Cable-Stayed Bridges Different Than Other Bridges?
Cable-stayed bridges can look similar to suspension bridges because both have towers and roadways that hang from cables. However, the two bridge types support the load of the roadway differently. This is due to the way the cables are connected to the towers.
In cable-stayed bridges, the cables are attached to the towers, bearing the load alone. Suspension bridges’ cables ride freely across the towers, sending the load to anchorages at either end.
What are the Pros and Cons of Cable-Stayed Bridges?
Compared to suspension bridges, cable-stayed bridges are faster to build, require less materials and can be constructed from identical pre-cast concrete sections. However, suspension bridges are still the first choice for long bridges because of their design.
This may not always be the case. More cable-stayed bridges are being built with longer spans as developments are made in bridge design and construction. The Russky Bridge in Russia is currently the largest cable-stayed bridge in the world, spanning 3,622 feet.
Cable-stayed bridges are sensitive to deformations during construction and require close monitoring, like all suspended structures. After being built, cable corrosion and weather-induced vibrations are among the main concerns for cable-stayed bridges. The unwanted vibrations can weaken cables and even lead to structural damage.
Where Did Cable-Stayed Bridges Come From?
The first known design of a cable-stayed bridge appears in an Italian book called “Machinae Novae,” written in 1595. However, engineers did not commonly use the design until the mid-20th century.
Sweden’s Strömsund Bridge is considered the first modern cable-stayed bridge, completed in 1956 with a 597-foot main span. Over the following years, this bridge type has seen a dramatic increase in usage around the world.
Some of the first cable-stayed bridges built in the U.S. still stand. The Ed Hendler Bridge, built in 1978 and spanning the Columbia River, is considered a landmark of Washington’s Tri-Cities area. Similarly, the 1987 Sunshine Skyway Bridge in Florida’s Lower Tampa Bay is now recognized as a state icon.
Sources: PBS, Bridge Engineering, STRUCTURE Magazine, Scientific American