Suspension bridges have tall towers connected by large cables that support the bridge deck. The document discusses the history and development of suspension bridges over centuries. It explains the key parts of a modern suspension bridge, including tall towers anchored deeply into the ground, main cables running between the towers and over the top in a parabolic curve, and suspender cables hanging down to connect the main cables to the bridge deck. The main cables are made of steel wires bundled tightly together to transfer loads into tension in the cables and compression in the towers.
Suspension bridges have tall towers connected by large cables that support the bridge deck. The document discusses the history and development of suspension bridges over centuries. It explains the key parts of a modern suspension bridge, including tall towers anchored deeply into the ground, main cables running between the towers and over the top in a parabolic curve, and suspender cables hanging down to connect the main cables to the bridge deck. The main cables are made of steel wires bundled tightly together to transfer loads into tension in the cables and compression in the towers.
Suspension bridges have tall towers connected by large cables that support the bridge deck. The document discusses the history and development of suspension bridges over centuries. It explains the key parts of a modern suspension bridge, including tall towers anchored deeply into the ground, main cables running between the towers and over the top in a parabolic curve, and suspender cables hanging down to connect the main cables to the bridge deck. The main cables are made of steel wires bundled tightly together to transfer loads into tension in the cables and compression in the towers.
Suspension bridges have tall towers connected by large cables that support the bridge deck. The document discusses the history and development of suspension bridges over centuries. It explains the key parts of a modern suspension bridge, including tall towers anchored deeply into the ground, main cables running between the towers and over the top in a parabolic curve, and suspender cables hanging down to connect the main cables to the bridge deck. The main cables are made of steel wires bundled tightly together to transfer loads into tension in the cables and compression in the towers.
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Modern Suspension Bridges
Abstract: Suspension bridges with their tall towers, long spans
and gracefully curving cables are beautiful examples of the work of civil engineers. How do the towers and cables carry the load of the bridge? Can a suspension bridge carry the greater load than a simple beam bridge? This simple project shows you to how to find it and how this will be helpful in real life?. What is the development of the suspension bridge in this project?.
and hundreds of years. One of the oldest suspension bridges still in
use today was built in China about 300 A.D. People still walk across the Anlan Bridge which was built more than 1,700 years later. Its cables were originally made of twisted bamboo grass. These were not replaced with steel cables until 1975. OK, let's put a cross piece across two tall towers and suspend the bridge from that:
Key Words: Introduction, Mechanism& Working Principle, Parts of
Suspension Bridge, How the Suspension Bridge Construction Occurs, Materials Used in Bridge Construction, Advantages & Disadvantages. Introduction: Engineers solve problems. One of the earliest problems humans faced as they began to travel was how to cross a body of water, like a river. Suppose lets have a question, Q: How do you think our oldest ancestors might have solved this problem?
Fig1: Suspending a bridge from a Crosspiece
This looks much better, except the crosspiece is essentially a beam bridge by itself and will sag enormously. Well, as long as we know the thing doing the suspending will sag anyway, why not make it cheaper and lighter by making it into a sagging cable and suspending the bridge from that?
A: Generally their suggestions are such as swimming, in a boat, a
tree log. If the river were deep or full of rocks and rapids, it would be too dangerous to swim or walk across. If the river was very wide, a fallen tree might not reach across. If they needed to cross the river many times, they would want something that could be used over and over by many peopleand that could hold heavy loads in carts or wagons. They would need to build a bridge. One of the things engineersspecifically structural engineers are most noted for is designing and building bridges. Bridges influence the development of cities, environments, and culture. They come in all shapes and sizes. One of the sturdiest, longest, and most elegant of these is the suspension bridge. Today we are going to learn about suspension bridges: what they look like and how they work. Although suspension bridges look as if they were invented with today's technology, they have been used for hundreds
Fig2: Suspending a Bridge with Large Cables
This approach is called a suspension bridge. But, if it were to be built exactly like drawn above, the two towers would try to fold in on each other:
A suspension bridge consists of cables anchored to the
earth at their ends and supported by towers at intermediate points. From these cables a floor or 'deck' is suspended. A suspension bridge creates its load-carrying capability through a balance of opposites: with the cables always in tension and the towers in compression. A suspension bridge suspends the roadway from its huge main cables, which extend from one end of the bridge to the other. Fig3: A Small Problem So, suspension bridges also have an extra set of cables on the outside to help keep the towers from collapsing inwards as shown here:
Fig4: A Better Idea
One of the tricks to building suspension bridges is how large you can make the distance between the two towers. Because of advances in engineering, bridge designers have been able to make that distance larger and larger. The following graph shows how that distance has increased. It came from a great article in the December 1997 Scientific American called Building the Biggest.
Known Suspension Bridge: GOLDEN GATE BRIDGE
The towers enable the main cables to be draped over long
distances. The cables, which are embedded in either solid rock or massive concrete blocks, carry most of the weight of the bridge. Inside the anchorages, the cables are spread over a large area to evenly distribute the load and to prevent the cables from breaking free. A modern suspension bridge can be easily identified by its elongated "M" shape. The Cables that go from the top of the towers down the ground are the backstays. The backstays are connected to the huge rock or concrete piers buried in the ground. The anchorages are also under tension, but since they, like the towers, are held firmly to the earth, the tension they experience is dissipated. Almost all suspension bridges have, in addition to the cables, a supporting truss system beneath the bridge deck (a deck truss). This helps to stiffen the deck and reduce the tendency of the roadway to sway and ripple. The backstays keep the towers from bending in. In addition to long span, the bridge was designed to resist huge earthquakes (8.5) and hurricane force winds (220MPH). Because suspension bridges are light, they can sometimes be damaged by winds that cause them to sway or gallop. Newer suspension bridges use steel plates or super strong steel cables. Cables work by putting the material into tension. Stone and concrete do not work in well in tension; they are too brittle and usually too heavy. A material in tension when its particles are being pulled apart. A suspension bridge has a curved tension member. Suspension bridges use a combination of tension and compression. The cables can only carry tension loads. By stretching across the towers, they pull down and create a compression in towers.
Suspension bridges come in two different designs:
1. The modern suspension bridge and 2. Cable-stayed Bridge. A modern suspension bridge can be easily identified by its elongated "M" shape. The cable-stayed bridge has more of an "A" shape. Instead of requiring two towers and four anchorages, the cables on a cablestayed bridge are run from the roadway up to a single tower where they are secured.
Fig5: Golden Gate Bridge
MECHANISM, WORKING PRINCIPLE OF THE PROJECT:
Fig7: Additional Improvements to the Bridge
The above figure (Fig 7 )shows the additional improvements to the Suspension Bridge. How the Construction Occurs: 1. Figure6: SUSPENSION BRIDGE
Where the towers are founded on underwater piers,
caissons are sunk and any soft bottom is excavated for a foundation. If the bedrock is too deep to be exposed by excavation or the sinking of a caisson, pilings are driven to the bedrock or into overlying hard soil, or a large concrete pad to distribute the weight over less resistant soil may be constructed, first preparing the surface with a bed of compacted gravel. (Such a pad footing can also accommodate the movements of an active fault, and this has been implemented on the foundations of the cablestayed Rio-Antirio bridge. The piers are then extended above water level, where they are capped with pedestal bases for the towers.
2. Where the towers are founded on dry land, deep foundation
excavation or pilings are used. PARTS OF SUSPENSION BRIDGE:
3. From the tower foundation, towers of single or multiple
columns are erected using high-strength reinforced concrete,
stonework, or steel. Concrete is used most frequently in modern
suspension bridge construction due to the high cost of steel. 4. Large devices called saddles, which will carry the main suspension cables, are positioned atop the towers. Typically of cast steel, they can also be manufactured using riveted forms, and are equipped with rollers to allow the main cables to shift under construction and normal loads. 5. Anchorages are constructed, usually in tandem with the towers, to resist the tension of the cables and form as the main anchor system for the entire structure. These are usually anchored in good quality rock, but may consist of massive reinforced concrete deadweights within an excavation. The anchorage structure will have multiple protruding open eyebolts enclosed within a secure space. 6. Temporary suspended walkways, called catwalks, are then erected using a set of guide wires hoisted into place via winches positioned atop the towers. These catwalks follow the curve set by bridge designers for the main cables, in a path mathematically described as a catenary arc. Typical catwalks are usually between eight and ten feet wide, and are constructed using wire grate and wood slats. 7. Gantries are placed upon the catwalks, which will support the main cable spinning reels. Then, cables attached to winches are installed, and in turn, the main cable spinning devices are installed. 8. High strength wire (typically 4 or 6 gauge galvanized steel wire), is pulled in a loop by pulleys on the traveler, with one end affixed at an anchorage. When the traveler reaches the opposite anchorage the loop is placed over an open anchor eyebar. Along the catwalk, workers also pull the cable wires to their desired tension. This continues until a bundle, called a "cable strand" is completed, and temporarily bundled using stainless steel wire. This process is repeated until the final cable strand is completed. Workers then remove the individual wraps on the cable strands (during the spinning process, the shape of the main cable closely resembles a hexagon), and then the entire cable is then compressed by a traveling hydraulic press into a closely packed cylinder and tightly wrapped with additional wire to form the final circular cross section. The wire used in suspension bridge construction is a galvanized steel wire that has been coated with corrosion inhibitors. 9. At specific points along the main cable (each being the exact distance horizontally in relation to the next) devices called "cable bands" are installed to carry steel wire ropes called Suspender cables. Each suspender cable is engineered and cut to precise lengths, and are looped over the cable bands. In some bridges, where the towers are close to or on the shore, the suspender cables may be applied only to the central span. Early suspender cables were fitted with zinc jewels and a set of steel washers, which formed the support for the deck. Modern suspender cables carry a shackle-type fitting. 10. Special lifting hoists attached to the suspenders or from the main cables are used to lift prefabricated sections of bridge deck to the proper level, provided that the local conditions allow the sections to be carried below the bridge by barge or other means. Otherwise, a traveling cantilever derrick may be used to extend the deck one section at a time starting from the towers and working outward. If the addition of the deck structure extends from the towers the finished portions of the deck will pitch upward rather sharply, as there is no downward force in the center of the span. Upon completion of the deck the added load will pull the main cables into an arc mathematically described as a parabola, while the arc of the deck will be as the designer intended usually a gentle upward arc for added
clearance if over a shipping channel, or flat in other cases such as a
span over a canyon. Arched suspension spans also give the structure more rigidity and strength. 11. With completion of the primary structure various details such as lighting, handrails, finish painting and paving are installed or completed. INPUT MATERIALS: [1] Steel Cables [2] Girders [3] Hangers [4] Water [5] Aggregates [6] Concrete [7] Sulphate Resisting Cement [8] Steel Plates [9] Mixers [10] Tremie Pipe [11] Polyethylene Sheet OUTPUT: By using the above materials we can plan, design and construct the suspension bridges. USES: 1) The suspension bridge is mainly used for when want to built a bridge over a long span (i.e for long distances), we cant built actual bridges in a river if the river was so long if that it is uneconomical. For decreasing the amount of construction these modern suspension bridges are developed. 2) Transfer huge amount of load over long span. 3) Communication, trading between the cities also increases. 4) Better to withstand earthquake movements than heavier and more rigid bridges. DISADVANTAGES:
I. Considerable stiffness or aerodynamic profiling may be required
to prevent the bridge deck vibrating under winds.
II. High amount of Cost for Construction
CONCLUSION: Finally this project shows you how the suspension bridges are, how they work, and the additional improvements that we added for the suspension bridge to withstand the loads, and the increment of workability and durability of the suspension bridge. References: http://en.wikipedia.org/wiki/Suspension_bridge http://www.pbs.org/wgbh/nova/bridge/build.html http://static.howstuffworks.com/pdf/ups-suspension-bridge.pdf Conclusion: This project shows you how the Modern Suspension Bridges are,how it works, why it is needed for transportation and the additional improvements to the bridge.
A Short Guide to the Types and Details of Constructing a Suspension Bridge - Including Various Arrangements of Suspension Spans, Methods of Vertical Stiffening and Wire Cables Versus Eyebar Chains