A cable stayed bridge is a design which has the weight of the bridge deck supported by several cables that run to a single tower or several towers, depending upon the size of the bridge. In most designs, the cables create a pattern that is either fan-like or a series of parallel lines, contrasting from a suspension bridge where the deck is supported by vertical cables.
The design of the cable stayed bridge has been known since at least the 16th century. It has been employed for use since at least the 19th century.
Here are the pros and cons of a cable stayed bridge design to consider.
List of the Pros of a Cable Stayed Bridge
1. It takes less time to build a cable stayed bridge.
One of the advantages of the cable stayed design for a bridge is that it doesn’t require the same degree of anchorages as other bridge designs. The deck for the bridge can be supported with fewer suspension cables as well. For smaller designs, a single tower may be enough to support the entire design. That means the construction time for this bridge design can be significantly less when compared to other modern bridge designs.
2. It is a strong bridge design.
Compared to the traditional suspension bridge design, the cables involved with a cable stayed bridge are capable of handling more pressure. That provides the deck with a greater level of consistency for travel. It keeps its shape better, even under heavy live loads, because the overall design has more rigidity. At the same time, they have a natural level of environmental resistance that permits them to remain a viable option after events, such as an earthquake.
3. It is an affordable design to build.
Most cable stayed bridge designs require fewer raw materials. They require fewer labor hours to complete. That combination means this bridge design option can be up to 30% cheaper than other bridge designs. For that reason, the cable stayed bridge has come back into prominence, since the late 20th century, as it can replace aging bridges that no longer respond positively to ongoing maintenance and support.
4. It can have each span connect to one another to create longer bridges.
The natural design of a cable stayed bridge somewhat limits the distance that it can safely span for consumers. What is unique about this design is that each deck section can connected to one another through a series of pylons and anchors, creating bridges of almost indefinite length. The Jiaxing-Shaoxing Sea Bridge in China is currently the widest and longest cable stayed bridge in the world today. It carries 8 lanes of traffic and is over 10,000 meters in length, extending across Hangzhou Bay. Even the main body of the bridge is over 2,600 meters in length.
5. It allows each cable to support the needs of every other cable.
What makes this design unique is that the cables with the bridge are permanent and temporary supports simultaneously. If more weight needs to be supported in one specific section, the bridge is able to accommodate this need by displacing the weight throughout the cable structures. At the same time, the cables are also used to permanently maintain the deck, permitting the bridge to be safely used in the first place.
6. It offers several different design options.
A cable stayed bridge can be built in a variety of ways, allowing each span to be created in a way that meets the needs of each community. A side-spar design has just one tower and is supported on just one side. A cantilever-spar design offers a single spar on one side of the span. There are multiple-span, extra-dosed, and cradle-system bridge designs all included as options for this type of bridge as well.
List of the Cons of a Cable Stayed Bridge
1. It can be an unstable design in certain environments.
A cable stayed bridge should not be installed in a region that is known to experience high wind speeds on a consistent basis. The rigidity of the bridge gives it more overall durability, though it comes at the cost of flexibility. High wind speeds can cause the bridge to rock back and forth, which can loosen the cables which support the deck. In severe wind events, it is even possible for a cable stayed bridge to completely fail.
2. It has a maximum length.
A cable stayed bridge is a good option for shorter spans that need to be crossed only. The maximum span recommended for this type of bridge design is just 1,000 meters. In comparison, the maximum span length recommendation for a traditional suspension bridge can be nearly twice as long. The Akashi Kaikyo Bridge in Japan, for example, is nearly 2,000 meters in length. The 10 longest suspension bridges in the world are all above 1,300 meters.
3. It can be a bridge design that is difficult to inspect.
The design of a cable stayed bridge places the cable bundle areas in regions that are difficult to access for a physical inspection. Anchorage areas may be fewer with this bridge design, but they are equally difficult to access for routine maintenance and inspection. That means the cost-savings feature of this bridge design is somewhat negated by higher overall ongoing support costs.
4. It can be susceptible to corrosion.
The cables of this bridge design must be specifically built to handle the unique environmental elements of the region where it is installed. That is because the cables are already prone to higher levels of fatigue compared to other bridge designs. Exposure to salt air elements in a coastal region, for example, could reduce the natural lifespan of the bridge and even make using it dangerous during its later years of life.
5. It is only advantageous for short or medium distance needs.
In most communities, the durability and flexibility of a suspension bridge is highly desired. That is why the cable stayed bridge fell out of favor in the early 20th century in the first place. What is bringing this bridge back is that it is suitable as a replacement in short or medium distance spans when a suspension bridge isn’t really practical.
The pros and cons of a cable stayed bridge show us that it is affordable and useful as a design, though it does have some placement limitations.