Views: 222 Author: Astin Publish Time: 2025-02-09 Origin: Site
Content Menu
● Suspension Bridge Components
● Suspension Bridge Design and Analysis
● Advantages of Suspension Bridges
● Disadvantages of Suspension Bridges
● Cable-Stayed Bridges vs. Suspension Bridges
● The Role of a Truss in a Suspension Bridge
● FAQ
>> 1. What is the primary function of a truss in a suspension bridge?
>> 2. How does a truss system contribute to the stability of a suspension bridge?
>> 3. What are the main components of a suspension bridge?
>> 4. How do suspension bridges handle compression and tension forces?
>> 5. What is the difference between a suspension bridge and a cable-stayed bridge?
A suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 1800s. Simple suspension bridges, which lack vertical suspenders, have a long history in many mountainous parts of the world. Suspension bridges are useful because they can be quite long and still work effectively.
The main components of a suspension bridge are:
- Two towers/pillars
- Two suspension cables
- Four suspension cable anchors
- Multiple suspender cables
- The bridge deck
As the name implies, suspension bridges suspend the roadway by cables, ropes, or chains from two tall towers. These towers support the majority of the weight as compression pushes down on the suspension bridge's deck and then travels up the cables, ropes, or chains to transfer compression to the towers. The towers then dissipate the compression directly into the earth. The supporting cables, on the other hand, receive the bridge's tension forces. These cables run horizontally between the two far-flung anchorages. Bridge anchorages are essentially solid rock or massive concrete blocks in which the bridge is grounded. Tensional force passes to the anchorages and into the ground.
In addition to the cables, almost all suspension bridges feature a supporting truss system beneath the bridge deck called a deck truss. This helps to stiffen the deck and reduce the tendency of the roadway to sway and ripple. A deck truss is often placed under the roadway of the bridge to provide additional stability.
The main cables of a suspension bridge will form a catenary when hanging under their own weight only. When supporting the deck, the cables will instead form a parabola, assuming the weight of the cables is small compared to the weight of the deck. One can see the shape from the constant increase of the gradient of the cable with linear (deck) distance, this increase in gradient at each connection with the deck providing a net upward support force. Combined with the relatively simple constraints placed upon the actual deck, that makes the suspension bridge much simpler to design and analyze than a cable-stayed bridge in which the deck is in compression.
Suspension bridges can easily cross distances between 2,000 and 7,000 feet (610 and 2,134 meters), enabling them to span distances beyond the scope of other bridge designs.
Given the complexity of their design and the materials needed to build them, they're often the most costly bridge option as well.
Types of suspension bridges include:
- Simple suspension bridge: the earliest known type of suspension bridge, and usually a footbridge. The deck is flexible and lies on the main cables, which are anchored to the earth.
- Underspanned suspension bridge: an early 19th-century descendant of the simple suspension bridge. The deck is raised on posts above the main cables.
- Stressed ribbon bridge: a modern descendant of the simple suspension bridge. The deck lies on the main cables, but is stiff, not flexible.
- Suspension bridge (more precisely, suspended-deck suspension bridge): the most familiar type. Though technically all the types listed here are suspension bridges, when unqualified with adjectives the term commonly refers to a suspended-deck suspension bridge. This type is suitable for use by heavy vehicles and light rail. The main cables are anchored to the earth. The deck is carried below the main cables by "suspenders" and usually is stiff.
- Self-anchored suspension bridge: a modern descendant of the suspension bridge, combining elements of a cable-stayed bridge. The main cables are anchored to the ends of the decks.
- Taper suspension bridge: a 19th century variant of the suspension bridge where the suspenders pull at an angle to the ground, nearly tangent with the main cable.
A pure suspension bridge is one without additional stay cables and in which the main cables are anchored in the ground. This includes most simple suspension bridges and suspended-deck suspension bridges, and excludes self-anchored suspension bridges.
Cable-stayed bridges and suspension bridges may appear to be similar, but are quite different in principle and in their construction. In suspension bridges, large main cables (normally two) hang between the towers and are anchored at each end to the ground. The main cables, which are free to move on bearings in the towers, bear the load of the bridge deck. Before the deck is installed, the cables are under tension from their own weight. Along the main cables smaller cables or rods connect to the bridge deck, which is lifted in sections. As this is done, the tension in the cables increases, as it does with the live load of traffic crossing the bridge. The tension on the main cables is transferred to the ground at the anchorages and by downwards compression on the towers. In cable-stayed bridges, the towers are the primary load-bearing structures that transmit the bridge loads to the ground. A cantilever approach is often used to support the bridge deck near the towers, but lengths further from them are supported by cables running directly to the towers. By design, all static horizontal forces of the cable-stayed bridge are balanced so that the supporting towers do not tend to tilt or slide and so must only resist horizontal forces from the live loads.
A truss bridge is a bridge whose load-bearing superstructure is composed of a truss, a structure of connected elements, usually forming triangular units. The connected elements, typically straight, may be stressed from tension, compression, or sometimes both in response to dynamic loads. There are several types of truss bridges, including some with simple designs that were among the first bridges designed in the 19th and early 20th centuries. A truss bridge is economical to construct primarily because it uses materials efficiently.
- Kingpost truss: One of the simplest truss styles to implement, the king post consists of two angled supports leaning into a common vertical support.
- Lattice truss (Town's lattice truss): This type of bridge uses a substantial number of lightweight elements, easing the task of construction. Truss elements are usually of wood, iron, or steel.
- Lenticular truss: A lenticular truss bridge includes a lens-shape truss, with trusses between an upper chord functioning as an arch that curves up and then down to end points, and a lower chord (functioning as a suspension cable) that curves down and then up to meet at the same end points. Where the arches extend above and below the roadbed, it is called a lenticular pony truss bridge. The Pauli truss bridge is a specific variant of the lenticular truss, but the terms are not interchangeable.
- Vierendeel truss: The Vierendeel truss, unlike common pin-jointed trusses, imposes significant bending forces upon its members—but this in turn allows the elimination of many diagonal elements. It is a structure where the members are not triangulated but form rectangular openings, and is a frame with fixed joints that are capable of transferring and resisting bending moments. While rare as a bridge type due to higher costs compared to a triangulated truss, it is commonly employed in modern building construction as it allows the resolution of gross shear forces against the frame elements while retaining rectangular openings between columns. This is advantageous both in allowing flexibility in the use of the building space and freedom in selection of the building's outer curtain wall, which affects both interior and exterior styling aspects.
- Waddell truss: Patented 1894 (U.S. patent 529,220); its simplicity eases erection at the site. It was intended to be used as a railroad bridge.
- Warren truss: The Warren truss was patented in 1848 by James Warren and Willoughby Theobald Monzani, and consists of longitudinal members joined only by angled cross-members, forming alternately inverted equilateral triangle-shaped spaces along its length, ensuring that no individual strut, beam, or tie is subject to bending or torsional straining forces, but only to tension or compression. Loads on the diagonals alternate between compression and tension approaching the center, with no vertical elements, while elements near the center must support both tension and compression in response to live loads. This configuration combines strength with economy of materials and can therefore be relatively light. The girders being of equal length, it is ideal for use in prefabricated modular bridges. It is an improvement over the Neville truss which uses a spacing configuration of isosceles triangles.
- Whipple truss: A Whipple truss, named after its inventor Squire Whipple, is usually considered a subclass of the Pratt truss because the diagonal members are designed to work in tension. The main characteristic of a Whipple truss is that the tension members are elongated, usually thin, and at a shallow angle, and cross two or more bays (rectangular sections defined by the vertical members).
- Wichert truss: The Wichert truss is a modified type of continuous truss which is statically determinate and helps avoid some of the other shortcomings of continuous trusses. It was patented in 1930 by Pittsburgh-based civil engineer Edward Martin Wichert (1883–1955). The defining feature of this truss type is a hinged kite-shaped section above each intermediate support. Only about ten Wichert truss bridges were ever built, mostly in Pennsylvania and Maryland. Of these, one of the best known is the Homestead Grays Bridge in Pittsburgh.
In suspension bridges, the truss system, typically a deck truss, is arranged beneath the bridge deck. Its main function is to stiffen the deck and minimize the swaying or rippling of the roadway. This is achieved by distributing loads across the bridge structure and enhancing its overall rigidity.
Different bridge structures are used for different purposes. One of the most common and mathematically interesting bridge types is the suspension bridge.
When constructing a bridge, architects must consider the compression and tension forces that the bridge is going to have to withstand – compression and tension. Consider a long piece of wood resting on two crates. As you put weight onto the middle of the wood, the top part of the wood shortens while the underside of the piece lengthens, making the middle sag and the ends lift up. This is because compression forces are shortening the top part of the wood and tension forces are elongating the underside of the wood.
In summary, a truss in a suspension bridge is a crucial component that adds stability and rigidity to the bridge deck. It works by distributing loads and reducing the tendency of the roadway to sway or ripple, ensuring the bridge's structural integrity and safety. While suspension bridges are known for their long spans and aesthetic appeal, the integration of a truss system is essential for their functionality and durability.
The primary function of a truss in a suspension bridge is to stiffen the deck and reduce the tendency of the roadway to sway and ripple. This is achieved by distributing loads across the bridge structure and enhancing its overall rigidity.
A truss system contributes to the stability of a suspension bridge by distributing loads across the structure and enhancing its overall rigidity. This helps to minimize the swaying or rippling of the roadway, ensuring the bridge's structural integrity and safety.
The main components of a suspension bridge are two towers/pillars, two suspension cables, four suspension cable anchors, multiple suspender cables, and the bridge deck.
Suspension bridges handle compression forces through the towers, which support the majority of the weight as compression pushes down on the bridge's deck and then travels up the cables to transfer compression to the towers. The towers then dissipate the compression directly into the earth. The supporting cables, on the other hand, receive the bridge's tension forces. These cables run horizontally between the two far-flung anchorages, where tensional force passes to the anchorages and into the ground.
In suspension bridges, large main cables hang between the towers and are anchored at each end to the ground. The main cables bear the load of the bridge deck, and smaller cables or rods connect to the bridge deck. In cable-stayed bridges, the towers are the primary load-bearing structures that transmit the bridge loads to the ground. Cables run directly to the towers, and all static horizontal forces are balanced so that the supporting towers do not tend to tilt or slide.
[1] https://en.wikipedia.org/wiki/Truss_bridge
[2] https://en.wikipedia.org/wiki/Types_of_suspension_bridges
[3] https://www.midasoft.com/bridge-library/suspension-bridges-unveiled-where-engineering-meets-elegance
[4] https://en.wikipedia.org/wiki/Suspension_bridge
[5] https://blog.enerpac.com/7-types-of-bridges-every-engineer-should-know-about/
[6] https://mathcentral.uregina.ca/beyond/articles/Architecture/Bridges.html
[7] https://science.howstuffworks.com/engineering/civil/bridge6.htm
[8] https://www.encardio.com/blog/types-of-bridges
[9] https://www.britannica.com/technology/suspension-bridge
