Cable Stayed Bridges | Cable Stayed Bridge Examples

Cable Stayed Bridges | Cable Stayed Bridge Examples

What is a Cable Stayed Bridge?

A cable-stayed bridge is a structural system with a continuous girder supported by inclined to stay cables from the towers.

From the mechanical point of view, the cable-stayed bridge is a continuous girder bridge supported by elastic supports.

The cable-stayed bridge ranks first for a span range of approximately from 115 to 600 m, which has a longer spanning capacity than that of cantilever bridges, arch bridges, and box caged bridges but shorter than that of a suspension bridge.

The earliest design of cable-stayed Bridge dates back to 1595, which is evident from the book of Machinae Novae. Several cable-stayed bridges were built in the early part of the 19th century. Still, it wasn’t until the 19 fifties that they started becoming prevalent like other bridge type, such as truss bridges, arch bridges, and suspension bridges.  

Several cable-stayed bridges collapsed due to a lack of understanding of such a system, particularly due to inadequate resistance. It wasn’t possible to tension the stay, and they would become slack under various load conditions.

A typical cable state of the bridge, this figure shows the main components of the cable state of the bridge, which is the tower, stayed cables, and Girders.

Basic Concept of Stayed Cable Bridge

The concept of cable-stayed bridges is simple as all the members and cable-stayed bridge mainly work on either tension or compression.

The stayed cable provides intermediate elastic support for carrying the vertical loads, acting on the main geared up to span a longer distance. To carry the load applied on the bridge deck, the cables need to sustain the tensile axial force, resulting in compression force and pulls pylons and girders.

Though there are also some bending moments or other forces in pylons and the main girders generally, their effects are much smaller than that of the axial forces.

It’s well known that actually loaded members are more efficient than flexible members, which contributes to the structural efficiency and economy of a cable-stayed bridge

Classifications and Configuration of Cable-Stayed Bridges.

This type of bridge can be classified based on three considerations.

Stay Cable Arrangements

According to the elongated Cable layout, the cable-stayed bridges can be classified into four types.

Mono Cable System.

The mono design uses a single cable from its towers and is one of the less types  of bridge used and  regularly built

 Fan Cable System 

 In  fan cable design,  all stayed cables connect to or pass over the top of the towers.

Modified Fan Cable System.

 Avoid difficulties in a fan cable system due to the laxation together of cable-stay the modified fan cable system is developed

Harp Cable System 

In the harp cable system, the cables are nearly parallel to each other so that the height of their fixed points on the tower is proportional to the distance around the tower to their positions on the deck.

Lateral Cable Arrangements 

The second consideration is the lateral cable arrangements and the lateral direction the cable system can be arranged as;

1.      One single plane above the centerline.

2.      Two planes, either vertical or inclined at the edges of the girder or 

3.      Three planes connect to the central line on both edges off together.

The Number of Spans or Towers

The third one is the number of spans or towers. The cable-stayed bridge can be designed as a single-span to expands three spans or multiple spans.

However, cable-stayed bridges having either three or two cable status spans are more widely used because the cable stays on the anchor pier and is important for the pylon’s stability.

When a bridge has more than three spans, the main problem is the lack of longitudinal restrained to the top of the intermediate pylons, which cannot be directly anchored to an approach pier.

Large deformations can occur in multiple span cable-stay of bridges under the live load. This problem can be solved in the following ways.

1.      By increasing the stiffness of pylons, as in using the A-frame embraced pylons.

2.      Using additional horizontal cables between tower tops directly transfers any out of balance forces to the anchor stays in the end spans. 

3.      By using additional cables to connect the top of the internal pilots to the adjacent pylons at deck level so that any out of balance forces are resisted by the stiffness of the pylon below deck 

4.      By using additional tie-down peers at span centers 

5.      By adding additional cables at the midspans,

Parts of Cable-Stayed Bridges

Cable-stayed bridges, are composed of cables, pylons, and bridge deck.

Bridge Cables

Cable stays are the key load carrying and transferring members in cable-stayed bridges. The main problems with the early cable-stayed bridges were deficiencies with the Anchorage system steel material and corrosion.

Bridge Pylons

The pylons can be designed as a single column projecting through the deck’s center but sometimes located on one side, such as in curved cable-stayed bridges.

Bridge Deck.

In general, the deck needs to resist both bending moments from the dead weight and live load on the axial force derived from the stay force’s horizontal component.

Therefore, unlike the deck in a suspension bridge, the deck can be designed as different sections or structural forms and cable-stay bridges.

Types of Bridge Decks

There are three types of decks.

1.      Steel deck 

2.      Concrete deck and

3.      Compose a deck.

Steel Deck

The steel deck was used for early cable-stayed bridges due to the high load-carrying capacity to weight ratio and larger span capacity between cable-stayed.

Besides, the reduction and deck weight can result in an economical design for large span bridges.

Concrete Deck Reinforces or Prestressed. 

Concrete decks can be made of precast elements, or they can be cast in a place. The concrete deck is suitable for medium spans because the cost of concrete is relatively low. Still, its weight increases the bridge’s dead load, thus requiring larger dimensions for cables, pylons, piers, and anchors structures.

Composite Deck 

Composite construction of a steel-concrete is a popular structural method. The optimal combination of the two most popular construction materials’ properties is steel and concrete, resulting in both safe and economic structures.

Analysis and Construction of Cable-Stayed Bridges. 

 Analysis of Cable-Stayed Bridge.

 Both static and seismic analysis should be performed on a cable-stayed bridge to analyze modern cable-stayed bridge finite element analysis; analysis is always necessary.

The pylon deck on the cable-stayed bridge will be moderate by a suitable element, and the fishbone model usually used to simulate the whole bridge.

The stayed can be represented with the small inertia on modified modules of elasticity that will model the stay’s Sag behavior. Besides, for considering the force transformation and load redistribution during the erection, stage by stay-based analysis is always necessary.

In addition to the static analysis, the dynamic analysis for determining a stayed Cable Bridge’s dynamic force, such as frequencies and vibration moods, should also be reaffirmed.

Construction of Stayed Cable Bridge

The first stay pylons and deck unit above the piers are erected and fixed to the piers. In the second stage, a new deck segment is erected by free cantilevering from the pylon, either symmetrical in both directions or into the main span. The stayed cables are installed and tension initially to relieve the bending moment in the deck. Stage two is repeated until the deck and middle span are connected.

The final stage before the connection of the deck mid-span cantilever condition should be carefully confirmed.

Pros and Cons of Stayed Cable Bridge

Pros of Stayed Cable Bridge

•  The construction method is a simple cantilever method.
• Typically built for a larger span and
• Simple to design as opposed to the suspension bridge.

Cons of Stayed Cable Bridge

• It may require a pier, or at least a tower on the other side of the site.
• More susceptible to damage by wind forces.
• Although cheaper than suspensions bridge, it can be more expensive for short spans than truss bridge Construction.

Summary Stayed Cable Bridge

 A cable-stayed bridge is very economical and has an elegant appearance due to the relatively small girder depth and has proved to be very competitive against other bridge types.

Besides, with the bridge design and construction development, more and more cable-stayed bridges are being built with longer spans.

Longest Cable Stayed Bridges in the World

Currently, the Russky Bridge in Russia is the largest cable-stayed bridge with walls longest this pan at 1104 m.(3,622 feets)