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PDF | Structural design requires a full understanding and knowledge of all the components comprising the structure. A suspension bridge is a. PDF | The sound modeling of any mechanical system requires careful experimental For complex structures such as suspension bridges, the. Introduction. When Norway's Hardanger suspension bridge opens next month it will have the. 10th longest main span in the world. It will, however, be unique.


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Seminar report On CABLE SUSPENSION BRIDGE To be submitted in Partial Fulfilment of the requirement for the Degree of Bachelor of. How can we increase the stiffness of a cable? in other words how can we reduce de vertical deflection of a cable caused by a point load?. PDF | 5+ minutes read | In this project, the structural analysis of suspension bridge is conducted using the computer program named as (CSi Bridge).

To browse Academia. Skip to main content. You're using an out-of-date version of Internet Explorer. Log In Sign Up. The Construction of a Suspension Bridge. Baris Evran.

Pdf suspension bridge

It has a rigid deck which lays on suspension cables which are in turn embedded in the deck. Deck follows a catenary arc between supports and is stressed in traction, which This bridge is usually made of concrete reinforced by steel tensioned cables and can carry vehicle traffic. Concrete plates are premade and placed to form the initial structure.

Sandbags are place upon the tiles to prestress cables that hold the tiles and gaps between the tiles are filled with concrete. When the concrete dries, sandbags are removed and cables compress, stiffening the bridge and making it more durable. This method of building appeared in mith century and was designed by Austrian engineer Josef Langer in American engineer Charles Bender patented this method in United States in Earliest bridges built with this method in United States were Three Sisters Bridges of Pittsburgh, built between and Suspension cables cannot be anchored until the deck is finished with this design so a false-work is used to hold them until then.

As depicted in Figure 1, in cable stayed bridges straight cables transfer deck loads directly to the pylon Walther et al. But as shown in Figure 2, in suspension bridges, there are main cables suspension cables that carry vertical cables. These vertical cables behave as restraints for the deck and transfer deck loads to the main cables. Figure 1: Cable Stay Bridge Credit by: Wikipedia Figure 2: Suspension Bridge Credit by: Wikipedia Usually main spans of suspension bridges are longer than cable stay bridges; therefore, decks of the suspension bridges have less stiffness in comparison with cable stay bridges.

As a result, suspension bridges have more vibration concerns. In addition, design and construction of suspension bridges are more complicated rather than cable stay bridges; and that's the reason why most of the failures of the cable bridges happened in suspension bridges.

Components of a Suspension Bridge Construction of various parts- A suspension bridge should consist of the components shown on the diagram, other elements are added for aesthetic purposes and design. The deck on a suspension bridge is also referred to as a roadway, where vehicles are allowed to pass to and from points A and B.

They can carry motorists, pedestrians, rail traffic etc. They are made out of steel reinforced concrete and each deck is of a large span. Steel Cables: The decking or the roadway is suspended by steel cables. They can be as thick as a tall male human, and are made up of many smaller steel cables; steel is used instead of iron because it is an alloy, which makes it superior in tension and compression and it is stronger. The smaller cables are fastened to one another forming one huge cable enough to hold up to , tonnes.

The suspenders connect the decking to the steel cables and help shape the bridge. Without the suspenders, the roadway would sway out of control; they help reinforce the decking even more as well as having steel cables.

The heavy weight of the steel cables are transferred onto the towers that help the bridge stay standing; the weight that is now supported by the towers is focused onto the ground, reinforcing the tower feet into the ground and keeping the bridge upright. Anchorage Block: These weigh more than the amount of cables that is holding up the deck; this is because it has to withstand a huge proportion of the roadway. Not only this, but it must be strong enough to endure the amount of road traffic and vehicles crossing the bridge at any time.

They are often made out of concrete as it is extremely heavy and strong. They appear at both ends of the bridge and preserve the tension from the steel cables. Foundation of Tower: The foundations are pushed far below the soil to keep the towers from tilting and to make sure that they are vertical and strong enough to withstand the weight from the cables.

Depending on the softness of the soil, depends on how far down the foundations go; if the soil is soft, then the foundation would be pushed further down. Not only this, but it helps stiffen the decking which reduces the probability of it swaying vertically just like it did in the Tacoma Narrows Bridge example.

Raw Materials Many of the components of a suspension bridge are made of steel. The girders used to make the deck rigid are one example. Steel is also used for the saddles, or open channels, on which the cables rest atop a suspension bridge's towers.

When steel is drawn stretched into wires, its strength increases; consequently, a relatively flexible bundle of steel wires is stronger than a solid steel bar of the same diameter. This is the reason steel cable is used to support suspension bridges. On some suspension bridges, the steel wires forming the cables have been galvanized coated with zinc.

The towers of most suspension bridges are made of steel, although a few have been built of steel- reinforced concrete.

The Manufacturing Process Construction of a suspension bridge involves sequential construction of the three Tower constructions that will stand in water begin with caissons a steel and concrete cylinder that acts as a circular dam that are lowered to the ground beneath the water, emptied of water, and filled with concrete in preparation for the actual towers.

Some bridges are designed so that their towers are built on dry land, which makes construction easier. If a tower will stand in water, its construction begins with lowering a caisson a steel and concrete cylinder that acts as a circular damn to the ground beneath the water; removing the water from the caisson's interior allows workers to excavate a foundation without actually working in water.

When the excavation is complete, a concrete tower foundation is formed and poured. As an example, consider the Akashi Kaikyo Bridge. Each of its two steel towers consists of two columns.

Each column is composed of 30 vertical blocks or layers , each of which is 33 ft 10 m Anchorages—structures that support the bridge's cables—are massive concrete blocks securely attached to strong rock formations. When the towers and anchorages have been completed, a pilot line must be strung along the cable's eventual path, from one anchorage across the towers to the other anchorage. A crane positioned between the columns lifted three sections into place on each column, completing a layer.

After completing a block on each column, the"bootstrapping" crane was jacked up to the next level, where it lifted the sections of the next layer into place. At appropriate intervals, diagonal bracing was added between the columns. They are massive concrete blocks securely attached to strong rock formations.

During construction of the anchorages, strong eyebars steel bars with a circular hole at one end are embedded in the concrete. Mounted in front of the anchorage is a spray saddle, which will support the cable at the point where its individual wire bundles see Step 5 fan out—each wire bundle will be secured to one of the anchorage's eyebars.

(PDF) The Construction of a Suspension Bridge | Baris Evran - musicmarkup.info

Various methods can been used to position the pilot line. Today, a helicopter might be used. Or the line might be taken across the expanse by boat and then lifted into position. When the pilot line is in place, a catwalk is constructed for the bridge's entire length, about 3 ft 1 m below the pilot line, so workers can attend to the cable formation. The free end of the wire is looped around a strand shoe a steel channel anchored to an eyebar. Between the This wheel carries the wire across the bridge's path, and the wire is looped around a strand shoe at the other anchorage; the wheel then returns to the first anchorage, laying another strand in place.

The process is repeated until a bundle of the desired number of wire strands is formed this varies from about strands to more than During the spinning, workers standing on the catwalk make sure the wire unwinds smoothly, freeing any kinks. As spools are exhausted, the end of the wire is spliced to the wire from a new spool, forming a continuous strand.

When the bundle is thick enough, tape or wire straps are applied at intervals Once the vertical cables are attached to the main support cable, the deck structure must be built in both directions from the support towers at the correct rate in order to keep the forces on the towers balanced at all times. A moving crane lifts deck sections into place, where workers attach them to previously placed sections and to the vertical cables that hang from the main suspension cables.

The wire coming off the spool is cut and secured to the anchorage.

Then the process begins again for the next bundle. The number of bundles needed for a complete cable varies; on the Golden Gate Bridge it is 61, and on the Akashi Kaikyo Bridge it is When the proper number have been spun, a special arrangement of radially positioned jacks is used to compress the bundles into a compact cable, and steel wire is wrapped around it.

Steel clamps are mounted around the cable at predetermined intervals to serve as anchoring points for the vertical cables that will connect the decking to the support cable. The structure must be built in both directions from the support towers at the correct rate in order to keep the forces on the towers balanced at all times.

In one technique, a moving crane that rolls atop the main suspension cable lifts deck sections into place, where workers attach them to previously placed sections and to the vertical cables that hang from the main suspension cables, Alternatively, the crane may rest directly on the deck and move forward as each section is placed.

Painting the steel surfaces and installing electric lines for lighting are examples of other finishing steps. In addition, ongoing maintenance procedures begin. For example, a permanent staff of 17 ironworkers and 38 painters continue to work daily on the Golden Gate Bridge, replacing corroding rivets and other steel components and touching up the paint that protects the bridge. Most deck designs are made from open trusses that allow wind to pass through. It is important to build the deck aerodynamically or else it will twist and could snap.

One of Tacoma Narrows Bridge. The truss work of the deck was too flexible and it snapped in strong winds. The Building Steps 1. First huge concrete caissons are sunk into the bedrock to provide a solid base for the towers. Next the towers are constructed on top of the caissons. Giant anchor points are created on both ends of the bridge to keep tension in the cables.

Then the main cables are strung across the span of the bridge. A temporary walkway is constructed beneath the main cables so that construction can begin on the road deck. Suspender cables are put into place as the road deck is built to provide strength. When the road deck is finished, a layer of concrete is poured over the steel, followed by a layer of asphalt. These cables are capable of withstanding tension but offer no resistance to compression. These types of bridges work in a completely different way to the arch bridge.

Compression The force of compression pushes down on the suspension bridge's deck, but because it is a suspended roadway, the cables transfer the compression to the towers, which dissipate the compression directly into the earth where they are firmly entrenched. Tension The supporting cables, running between the two anchorages, are the lucky recipients of the tension forces.

The cables are literally stretched from the weight of the bridge and its traffic as they run from anchorage to anchorage. 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.

They come in two different designs: The cable-stayed bridge does not require two towers and four anchorages as does the suspension bridge. Instead, the cables are run from the roadway up to a single tower where they are secured.

On the Severn Bridge, the two main cables act a bit like a washing line. The tension in a washing line supports the weight of the clothes that are pegged to it. In the same way, the tension in the main cables supports the weight of the deck and traffic.

The bridge deck is hung from the main cables using wire hangers rather than clothes pegs. And because the main cables are held up by the towers, the weight of the whole bridge is carried down through the towers, on to the underlying foundations. If you put something heavy on a washing line, it will sag at that point. With a suspension bridge, the road is supported by a stiffening girder, which spreads out the weight of the traffic, so avoiding excessive sag under an exceptional load.

If you hang something on a washing line away from the centre, the point will not only sag but it will also move towards the nearest end try it! Similarly, as a heavy load travels over a suspension bridge, it will not only dip downwards at the point of the load, it will also move longitudinally towards the nearest tower. If you stand on the walkway of the Severn Bridge, you can feel it moving as the traffic travels over it.

If you stand by one of the towers and watch the expansion joint, you can sometimes see the whole bridge moving as the weight of the traffic travels across. We should not worry that the bridge moves. It is meant to do this. This is how it absorbs the weight of the traffic and transfers it into the main cables. Diagram showing the main loads in a suspension bridge The tension in the main cables carries the whole weight of the bridge deck and the traffic.

This tension is resisted by the anchorages at each end, just as the tension in a washing line is resisted by whatever it is tied to at each end. And because the main cables are held up by the towers, the weight of the whole bridge is transferred through the towers to the ground. Why do bridges collapse? Bridges don't fail very often, but when they do, the results are spectacular and unforgettable.

Once you've seen the footage of the Tacoma Narrows bridge resonating in a gale bucking back and forth before the deck breaks up and crashes to the river below, you'll never forget it. Imagine how terrifying it would have been if you'd been on the bridge at the time!

Bridges always collapse for exactly the same reason: A force becomes too great for one of the components in the bridge maybe something as simple as a single rivet or tie-bar , which immediately fails. That means the load on the bridge suddenly has to be shared by fewer components, so any one of them might also be pushed beyond its limit. Sooner or later, another component fails, then another—and so the bridge collapses in a kind of domino effect of failing materials. This is the remains of the IW Mississippi River bridge a steel-trussed arch bridge that used to carry a very busy highway over the river.

It collapsed unexpectedly in , killing 13 people and injuring more. A report into the disaster found that a metal plate had ripped along a line of rivets, causing a catastrophic failure.

Ironically, the bridge was carrying a massive extra load of construction equipment for repairs and reinforcement at the time.

Riddled with fatigue cracks and corrosion, it had been deemed "structurally deficient" as far back as There are two different ways in which a bridge component can fail catastrophically: First, and simplest, it might be too weak to cope with a sudden transient load.

If a bridge is designed to carry no more than cars, but heavy trucks drive onto it instead, that creates a dangerous, transient load. The load on the deck firstly travels into the deck. From the deck the load will travel through the suspenders and into the main cable.

The load in the cable will then travel to the top of each of the two towers, through the saddle and down the towers into the ground. So as you can see the construction process of a suspension bridge is the reverse of the load path. In principal the stages are straight forward but later you will see some risk and construction problems involved in the construction of suspension bridges. Construction Problems There are two different types of construction problem.

The first type would be something such as a bridge being unsuccessful and collapsing after it has been built. Secondly you have the problems that arise from the construction process and the effect it has on people and the environment. A prime example of a construction problem would be the Tacoma Narrows Bridge. This was a bridge that when completed in was the third longest suspension bridge in the world. It was designed to withstand winds of mph but when it collapsed there was a wind of just 42 mph.

After the bridge was opened it was soon noticed that the bridge moved not only from side to side but up and down which led to additional cables and hydraulic buffers being fitted to try and stabilize the bridge.

Pdf suspension bridge

Unfortunately these attempts failed and four months after opening the bridge collapsed as pictured. Some people have put the collapse down to resonance but one thing that was learnt from the collapse is that now all new bridges have scale models tested in wind tunnels to make sure they can withstand winds. The second type of construction problems are those that arise when the work is being carried out, these can be anything from disrupting the local residents and the environment or not having a power source in place to operate machinery.

Certain projects that are carried out could be in rural areas. This means that there may not be any utilities in place such as electricity to run offices and lighting and any other basic facilities that will be required for the job and therefore it may mean generators would need to be put into place first. Secondly you may find that people and the environment are affected. The environmental aspects are mentioned later in this report.

However an example of how people could be affected is by the way in which materials are transported to the site. When constructing a suspension bridge over a river an alternative method to transporting materials over land would be to use the river to transport larger components to the site.

So as you can see some construction problems that occur can be thought through before they take place such as the transportation of materials and the use of utilities on site. However some problems are encountered along the way with a far greater impact than anyone would have expected, for example the wind affecting the Tacoma Narrows Bridge. Even after strengthening the bridge the problem was not resolved which ultimately lead to its collapse.

Safety Aspects Bridge safety is a very important factor in bridge design, construction, maintenance and repair. They inspect their bridges fully and carry out any repairs that may be required.

Some examples of the types of work that they carry out include repainting steel work that is exposed to the elements as well as repairing joints such as saddles mentioned earlier in the report.

State and local governments assess different bridges and then if they feel that work is needed on those bridges they apply for funds to carry the work out.

It is the only suspension bridge across the non-tidal Thames. Here, the chains are made from flat wrought iron plates, eight inches mm wide by an inch and a half 38mm thick, rivetted together.

Wire-cable The first wire-cable suspension bridge was the Spider Bridge at Falls of Schuylkill , a modest and temporary footbridge built following the collapse of James Finley's nearby Chain Bridge at Falls of Schuylkill The footbridge's span was m, although its deck was only 0. Development of wire-cable suspension bridges dates to the temporary simple suspension bridge at Annonay built by Marc Seguin and his brothers in It spanned only 18 m.

The first permanent wire cable suspension bridge was Guillaume Henri Dufour Saint Antoine Bridge in Geneva of , with two 40 m spans. Designed by Charles Ellet, Jr and completed in , it had a span of m. Ellet's Niagara Falls Suspension Bridge —48 was abandoned before completion. It was used as scaffolding for John A. Roebling double decker railroad and carriage bridge The Otto Beit Bridge —39 was the first modern suspension bridge outside the United States built with parallel wire cables.

Types of Suspension Bridges Suspension bridges are bridges whose deck is held in place by suspender cable which hang vertically from suspension cables. But they are not all the same. They use different techniques and materials to achieve the same thing — span distances that could not be crossed differently. It is also known as a rope bridge, swing bridge, suspended bridge, hanging bridge and catenary bridge and is the oldest variant of the suspended bridge.

The deck of this bridge follows is arched downwards and upwards and has additional ropes at a higher level which form the handrail. It is a pedestrian bridge and cannot carry modern roads and railroads. It has towers and, from them, cables that hold up the road deck. These cables transfer the weight of the deck, by tension, to the towers and then to the ground by cables whose ends are anchored.

This type can carry heavy vehicles and light rail. The first designs of this type of bridge appeared in 16th century but they were not built until 18th century when more materials appeared which allowed for this type of bridge to be made. Longest suspension bridges of today are of this design. It is a very rare design in practice because its deck is not too stable. Hammersmith Bridge has parts of the roadway built in this manner. It has a rigid deck which lays on suspension cables which are in turn embedded in the deck.

Deck follows a catenary arc between supports and is stressed in traction, which This bridge is usually made of concrete reinforced by steel tensioned cables and can carry vehicle traffic.

Concrete plates are premade and placed to form the initial structure. Sandbags are place upon the tiles to prestress cables that hold the tiles and gaps between the tiles are filled with concrete. When the concrete dries, sandbags are removed and cables compress, stiffening the bridge and making it more durable. This method of building appeared in mith century and was designed by Austrian engineer Josef Langer in American engineer Charles Bender patented this method in United States in Earliest bridges built with this method in United States were Three Sisters Bridges of Pittsburgh, built between and Suspension cables cannot be anchored until the deck is finished with this design so a false-work is used to hold them until then.

As depicted in Figure 1, in cable stayed bridges straight cables transfer deck loads directly to the pylon Walther et al. But as shown in Figure 2, in suspension bridges, there are main cables suspension cables that carry vertical cables. These vertical cables behave as restraints for the deck and transfer deck loads to the main cables.

Figure 1: Cable Stay Bridge Credit by: Wikipedia Figure 2: Suspension Bridge Credit by: Wikipedia Usually main spans of suspension bridges are longer than cable stay bridges; therefore, decks of the suspension bridges have less stiffness in comparison with cable stay bridges. As a result, suspension bridges have more vibration concerns. In addition, design and construction of suspension bridges are more complicated rather than cable stay bridges; and that's the reason why most of the failures of the cable bridges happened in suspension bridges.

Components of a Suspension Bridge Construction of various parts- A suspension bridge should consist of the components shown on the diagram, other elements are added for aesthetic purposes and design. The deck on a suspension bridge is also referred to as a roadway, where vehicles are allowed to pass to and from points A and B.

Suspension-Bridge.pdf - Harazaki I Suzuki S Okukawa...

They can carry motorists, pedestrians, rail traffic etc. They are made out of steel reinforced concrete and each deck is of a large span. Steel Cables: The decking or the roadway is suspended by steel cables. They can be as thick as a tall male human, and are made up of many smaller steel cables; steel is used instead of iron because it is an alloy, which makes it superior in tension and compression and it is stronger.

The smaller cables are fastened to one another forming one huge cable enough to hold up to , tonnes. The suspenders connect the decking to the steel cables and help shape the bridge.

Without the suspenders, the roadway would sway out of control; they help reinforce the decking even more as well as having steel cables. The heavy weight of the steel cables are transferred onto the towers that help the bridge stay standing; the weight that is now supported by the towers is focused onto the ground, reinforcing the tower feet into the ground and keeping the bridge upright.

Anchorage Block: These weigh more than the amount of cables that is holding up the deck; this is because it has to withstand a huge proportion of the roadway. Not only this, but it must be strong enough to endure the amount of road traffic and vehicles crossing the bridge at any time.

They are often made out of concrete as it is extremely heavy and strong. They appear at both ends of the bridge and preserve the tension from the steel cables. Foundation of Tower: The foundations are pushed far below the soil to keep the towers from tilting and to make sure that they are vertical and strong enough to withstand the weight from the cables.

Depending on the softness of the soil, depends on how far down the foundations go; if the soil is soft, then the foundation would be pushed further down.

ppt on suspension bridges

Not only this, but it helps stiffen the decking which reduces the probability of it swaying vertically just like it did in the Tacoma Narrows Bridge example. Raw Materials Many of the components of a suspension bridge are made of steel. The girders used to make the deck rigid are one example. Steel is also used for the saddles, or open channels, on which the cables rest atop a suspension bridge's towers.

When steel is drawn stretched into wires, its strength increases; consequently, a relatively flexible bundle of steel wires is stronger than a solid steel bar of the same diameter. This is the reason steel cable is used to support suspension bridges. On some suspension bridges, the steel wires forming the cables have been galvanized coated with zinc.

The towers of most suspension bridges are made of steel, although a few have been built of steel- reinforced concrete. The Manufacturing Process Construction of a suspension bridge involves sequential construction of the three Tower constructions that will stand in water begin with caissons a steel and concrete cylinder that acts as a circular dam that are lowered to the ground beneath the water, emptied of water, and filled with concrete in preparation for the actual towers.

Some bridges are designed so that their towers are built on dry land, which makes construction easier. If a tower will stand in water, its construction begins with lowering a caisson a steel and concrete cylinder that acts as a circular damn to the ground beneath the water; removing the water from the caisson's interior allows workers to excavate a foundation without actually working in water.

When the excavation is complete, a concrete tower foundation is formed and poured. As an example, consider the Akashi Kaikyo Bridge. Each of its two steel towers consists of two columns. Each column is composed of 30 vertical blocks or layers , each of which is 33 ft 10 m Anchorages—structures that support the bridge's cables—are massive concrete blocks securely attached to strong rock formations. When the towers and anchorages have been completed, a pilot line must be strung along the cable's eventual path, from one anchorage across the towers to the other anchorage.

A crane positioned between the columns lifted three sections into place on each column, completing a layer. After completing a block on each column, the"bootstrapping" crane was jacked up to the next level, where it lifted the sections of the next layer into place.

At appropriate intervals, diagonal bracing was added between the columns. They are massive concrete blocks securely attached to strong rock formations. During construction of the anchorages, strong eyebars steel bars with a circular hole at one end are embedded in the concrete.

Mounted in front of the anchorage is a spray saddle, which will support the cable at the point where its individual wire bundles see Step 5 fan out—each wire bundle will be secured to one of the anchorage's eyebars.

Various methods can been used to position the pilot line. Today, a helicopter might be used. Or the line might be taken across the expanse by boat and then lifted into position. When the pilot line is in place, a catwalk is constructed for the bridge's entire length, about 3 ft 1 m below the pilot line, so workers can attend to the cable formation.

The free end of the wire is looped around a strand shoe a steel channel anchored to an eyebar. Between the This wheel carries the wire across the bridge's path, and the wire is looped around a strand shoe at the other anchorage; the wheel then returns to the first anchorage, laying another strand in place.

The process is repeated until a bundle of the desired number of wire strands is formed this varies from about strands to more than During the spinning, workers standing on the catwalk make sure the wire unwinds smoothly, freeing any kinks. As spools are exhausted, the end of the wire is spliced to the wire from a new spool, forming a continuous strand. When the bundle is thick enough, tape or wire straps are applied at intervals Once the vertical cables are attached to the main support cable, the deck structure must be built in both directions from the support towers at the correct rate in order to keep the forces on the towers balanced at all times.

A moving crane lifts deck sections into place, where workers attach them to previously placed sections and to the vertical cables that hang from the main suspension cables.

The wire coming off the spool is cut and secured to the anchorage. Then the process begins again for the next bundle. The number of bundles needed for a complete cable varies; on the Golden Gate Bridge it is 61, and on the Akashi Kaikyo Bridge it is When the proper number have been spun, a special arrangement of radially positioned jacks is used to compress the bundles into a compact cable, and steel wire is wrapped around it.

Steel clamps are mounted around the cable at predetermined intervals to serve as anchoring points for the vertical cables that will connect the decking to the support cable.

The structure must be built in both directions from the support towers at the correct rate in order to keep the forces on the towers balanced at all times. In one technique, a moving crane that rolls atop the main suspension cable lifts deck sections into place, where workers attach them to previously placed sections and to the vertical cables that hang from the main suspension cables, Alternatively, the crane may rest directly on the deck and move forward as each section is placed.

Painting the steel surfaces and installing electric lines for lighting are examples of other finishing steps. In addition, ongoing maintenance procedures begin. For example, a permanent staff of 17 ironworkers and 38 painters continue to work daily on the Golden Gate Bridge, replacing corroding rivets and other steel components and touching up the paint that protects the bridge. Most deck designs are made from open trusses that allow wind to pass through.

It is important to build the deck aerodynamically or else it will twist and could snap. One of Tacoma Narrows Bridge. The truss work of the deck was too flexible and it snapped in strong winds.

The Building Steps 1. First huge concrete caissons are sunk into the bedrock to provide a solid base for the towers. Next the towers are constructed on top of the caissons.

Giant anchor points are created on both ends of the bridge to keep tension in the cables. Then the main cables are strung across the span of the bridge. A temporary walkway is constructed beneath the main cables so that construction can begin on the road deck. Suspender cables are put into place as the road deck is built to provide strength. When the road deck is finished, a layer of concrete is poured over the steel, followed by a layer of asphalt.

These cables are capable of withstanding tension but offer no resistance to compression. These types of bridges work in a completely different way to the arch bridge.

Compression The force of compression pushes down on the suspension bridge's deck, but because it is a suspended roadway, the cables transfer the compression to the towers, which dissipate the compression directly into the earth where they are firmly entrenched. Tension The supporting cables, running between the two anchorages, are the lucky recipients of the tension forces. The cables are literally stretched from the weight of the bridge and its traffic as they run from anchorage to anchorage.

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. They come in two different designs: The cable-stayed bridge does not require two towers and four anchorages as does the suspension bridge. Instead, the cables are run from the roadway up to a single tower where they are secured.

On the Severn Bridge, the two main cables act a bit like a washing line. The tension in a washing line supports the weight of the clothes that are pegged to it.

Suspension Bridge Seminar PPT with PDF Report

In the same way, the tension in the main cables supports the weight of the deck and traffic. The bridge deck is hung from the main cables using wire hangers rather than clothes pegs. And because the main cables are held up by the towers, the weight of the whole bridge is carried down through the towers, on to the underlying foundations.

If you put something heavy on a washing line, it will sag at that point. With a suspension bridge, the road is supported by a stiffening girder, which spreads out the weight of the traffic, so avoiding excessive sag under an exceptional load. If you hang something on a washing line away from the centre, the point will not only sag but it will also move towards the nearest end try it!