MODERN SUSPENSION BRIDGES
Modern suspension bridges are a very fascinating topic and a vast subject to discuss. In this dissertation, the primary objective will be to get a better understanding about suspension bridges in general. Firstly, the reader can get to know about the history of suspension bridges, the development over the years, which are clearly explained. Also, general understandings of common bridges are described too. In addition, the several different types of suspension bridges in particular are described in detail, along with the types of suspension cables which are very important to the suspension bridges built nowadays. Bridge designing is an important aspect too. This too is explained in detail in relation to the factors, and comparisons of classical design techniques with modern ones. Furthermore, structural analysis of the suspension bridges of the modern era is described later on, with modern construction techniques shown in a sequential form. Finally, a case study about the Akashi Kaikyo Bridge is looked into in detail. It is based on most of the topics discussed and compares some of the methods explained before in the previous chapters.
Suspension bridges are most probably the most extraordinary form of bridges made by mankind today. They are mainly noted for the long spans and dynamic beauty. Suspension bridges have a steel cables supported by high towers. A roadway hangs through the help of the steel cables. In addition, suspension bridges have a minimum of two main cables. They extend from one end to the other end of the bridge. Attached to the main cables are suspended cables, which hang and have the other end attached to the roadway.
Some people often confuse suspension bridges with cable-stayed bridges. One of the main differences between them is that in suspension bridges, the cables are not directly connected to the towers and they aren't connected to the bridge either. There's a hole on the top of the tower, where the cables go through.
Modern suspension bridges have probably the longest spans among other bridges in today's world. Very large distances are being able to cross with the help of these glorious man-made wonders. Moreover, mankind is capable of crossing deep waters, cannons, gorges, owing to these structures. Also, in areas where construction of supporting piers is difficult, suspension bridges can come in handy. They are ideal for covering busy waterways. The need for multiple towers is also done away with because the towers can be located faraway at a distance. The Akashi-kaikyo bridge, located in Japan boasts of being the longest suspension bridge in the world, which has a over mile long span, which is very long compared to others which have around 4000 ft. Massive bridges such as the one mentioned above, have very wide cables, which weigh around thousand pounds per foot. Thus, the cables are spun in place. The suspension bridge designing is not a very complicated process. If the methods are followed properly the goal can be achieved. However, construction of suspension bridges can differ from each bridge, because of the environment conditions. It is a known fact that suspension bridges are bridges made from leading technology today, yet very few are aware that there were old forms of suspension bridges during the past centuries.
Not to mention the beauty and remarkable structure they are, which are beyond doubt eye pleasing sites, and more often than not they are land marks for certain countries. Some famous suspension bridges in the world include New York's Brooklyn Bridge and San Francisco's iconic Golden Gate Bridge and the longest of them, Japan's Akashi Kaikyo Suspension Bridge.
History of Suspension Bridges
The origins of the suspension bridge go back a long way in history. Primitive suspension bridges, or simple crossing devices, were the fore bears to today's modern suspension bridge structures. Suspension bridges were constructed with iron chain cables over two thousand years ago in China and a similar record has been left in India. The iron suspension bridge, assumed to have originated in the South East Asia, appeared in Europe in the 16th century and was later developed in the 18th century. Although wrought iron chain was used as the main cables in the middle of the 18th century, a rapid expansion of the center span length took place in the latter half of the 19th century triggered by the invention of steel. Today, the suspension bridge is a most suitable type for very long span bridges and actually represents more than 20 or more of all the longest span bridges across the world.
The begining of the Modern Suspension Bridge
The modern suspension bridge originated in the 18th century when the developement of the bridge structure and the production of iron started on a full scale basis. As time passed, bridges started developing features with truss stiffening girders which gave more rigidity to distribute the load through the hanger ropes and thus prevents excessive deformation of the cable. In the first half of the 20th century in the United States, the progress of the center span length was seen. The AS method or aerial spinning method was used for constructing parallel wire cables was invented. The technology was used all over the country and the use of steel wires also came into being. The Brooklyn Bridge which is hailed as the first modern suspension bridge, was constructed across New Yorks East river over a period of 14 years. Remarkable suspension bridges were being made across Europe even though their center span lengths were quite short. In th UK, the construction of some suspension bridges revolutionized suspension bridge technology. Moreover, there were further developement in Asia around the ‘70s. In Japan, research for the construction of the Honshu-Shikoku bridges was begun by the civil engineers society. There were many completed bridges which used many technology developed methods. In Hong Kong China, a combined railway and raod way bridge with a centre span of 1377m, was completed in 1997. The construction of long-span suspension bridges of 1000 m is currnetly considered a remarkable achievement. Besides these suspension bridges, the planning of additional long-span bridges came into being. 
BRIDGES - A General Insight
Bridges can be defined in short as structures which carry people and vehicles across mostly natural impediments. In early day's people travelled by foot or some used carts, as the roads were connected from villages to towns. However, even though people managed to cross rivers or openings without many difficulties, when it came to carrying heavy loads, mainly with horse ridden vehicles, and also when the landscape was unsafe, a solution needed to be done. This is when permanent bridges played a very important role in transportation systems across the world. 
Bridges in the past were built from wood, stones and fibers and other local materials. Nowadays most bridges contain concrete, steel and wood frame works with roadways made up of concrete as well. Several different types of shapes and materials of bridges are used in order to compensate with the type of traffic as well as Mother Nature, i.e. talking of wind floods, etc. 
Bridges are never identical. There are various types of bridges made by mankind. Arch bridges, truss bridges, cantilever bridges, cable-stayed bridges, and suspension bridges to name a few. These are mostly combination of different kinds of bridges. In addition, many bridges are withstood by at least two supports, placed in the ground. They are known as abutments. There are additional supports called piers, which are set on the middle of the bridge. A span of a bridge is crucial in a bridges outcome. It is referred to as the distance between two piers, two abutments or a pier and an abutment. Shorter span bridges have only abutments, while longer span or multi-span bridges have piers as well for support. 
How Bridges Work
When looking at how a bridge needs to be, in order to fulfil its purpose, one can say it is all connected to physics. Bridges work by going against the gravitational force. It has to support its weight and the load of people or vehicles. Thus it needs to be made strong enough to withstand the pull of gravity. For example when we hold a piece of tissue on our hands, and then put a heavy book or any object on top of the tissue, the book will definitely break got through the tissue. This proves that the tissue needs more strength to hold the weight of the book. The same principle is applied to bridges as well. 
When going detail into the behaviour of bridges and how it works, it's clearly evident that bridges more often than not work on two main forces, tension and compression. These forces need to be balanced in order to make the bridge stable. An example to this can be shown by placing a flexible object between two fingers, say the thumb and index finger. It can be clearly seen that one side would be longer and bent outwards, while the other side is shorter and bent inwards. The conclusion is that the lengthen side is under going tension while the shorten side is under going compression. Again the same principle is applied to bridges as well. 
When analyzing different materials, one can say that the strength of all of them will be different. Steel, concrete, stone wood are some materials used to make bridges. Steel is stronger than wood, and is very flexible as well. Thus it can take more tension and compression when compared other materials. Moreover, stone could take in lots of compression but, when under tension it can crack. All these need to be considered when designing a bridge, and not to mention the fact that these bridge materials depend on the site requirements as well, like length and terrain etc. Thus the amount of stress these materials could resist and type of material should be analyzed appropriately. 
TYPES OF SUSPENSION BRIDGES
Suspension bridges are categorized into parts such as, types of suspenders, types of cable anchoring, continuity of stiffening girders, and number of spans. When relating to number of spans, they are further narrowed down to into single-span, two-span, or three span suspension bridges with two towers, and multi-span suspension bridges which have three or more towers, as shown in the figure above. Out of these types, the three-span suspension bridges are the frequently used ones. In multi span suspension bridges, due to the load conditions the horizontal displacement of the tower tops tend to increase, thus ways to control such situations may happen to be compulsory. Suspension bridge design can be organized into two different criteria, the elongated ‘M' shape suspension bridge, and the lesser known ‘A' shape, similar to cable-stayed design. A majority of suspension bridges have a supporting truss system below the deck of the bridge, apart from the cables. The advantage of this is that, it reduces the tendency of the road from swaying and also makes the deck stiffer. Some types of suspension bridges that follow these designs are listed below.
* Simple suspension bridges
Simple suspension bridges are bridge types, used in early days, formed from native material, and ropes in certain areas of South America. Due to the limited time of the resources, these rope bridges need to be renewed in time. Rope components, however, are made by families as contributions to helping the society. 
· Self-anchored suspension bridges
In self-anchored suspension bridges, the main cables attach to the ends of the road deck, unlike other types of suspension bridges, in which the main cables attach to the ground through massive anchorages. Tension and compression forces are experienced. The compression being equal to the horizontal component and tension equal to the vertical, and it si balanced from the road decks own weight. The effect of this design shows that the suspension bridges do not apply any horizontal forces towards the ground. The foundations of the bridge need to only support the bridge's weight. Thus, self anchored suspension bridges are more appropriate for construction of elevated piers, and areas where the soil is unstable, which makes the anchorages difficult to build. 
· Suspended-Deck Suspension Bridges
Suspended-deck suspension bridge, as the name suggests, the cables are suspended linking the towers, as an alternative for the deck trailing the downward arc of the main load-bearingcables, and verticalsuspender cableshold the weight of the deck beneath, upon which traffic crosses. They are modern bridges which are capable of carryingvehiclesandlight rail. The setting up of this sort, allows the deck to be in the same position or to the arc slightly upward for further clearance. 
* Un-Stiffened Suspension Bridges
These types of bridges comprise of floors, excluding stiffening girders (trusses), that suspend from cables. Therefore bridges of this sort are more appropriate where the live load, and wind load would not cause a major deformation among the cables. Examples of live load, which are very light, are footbridges. Also, bridges with a huge dead load yet no considerable live load can be considered as examples. 
* Stiffened Suspension Bridges
The cables are very flexible, in stiffened suspension bridges, which are hardened or stiffened by suspended girders (trusses). Owing to the live loads, these types of bridges reduce local changes in roadway slope. The beams of the floor structure are framed into stiffening girders and hangers going through to the cables, hold up these girders.
* Multi-span Suspension Bridges
Multi-span bridges, as the name suggests, are simply the grouping of two or more adjoining suspension bridges, which share the same anchorage. Furthermore, the bridge's towers are attached by a cable to help the unbalanced live loads from restraining movements of the tower tops. 
Suspension Bridge Cables
Modern Bridge cables are made from several strands of wire, unlike early days, where the main suspension cables were made from chains or linked bars. The cables used now, helps to increase the redundancy. This means that, when there is a one bad link or eye-bar, it can cause failure of the whole bridge. But even though a few strands out of hundreds show a defect, there isn't a great issue. ‘The malfunction of a sole eyebar was the reason of the breaking down of theSilver Bridgeon theOhio River.' Furthermore, as number of spans increase, engineers find it not feasible to carry larger chains into positions, however wire strand cables could be organized in great amount above ground level. To get into more detail about suspension bridge cables, there are a few types mentioned below, with diagrams.
1. Parallel Wire Cables - Cables that are invented of huge amount of singular wires, which are parallel to each other are consigned to parallel wire cables. There is no twisting of wires or cables. Individual wires are ‘spun' by setting up on the bridge and compacted together later on, which eventually forms a round cross-section. Mammoth structures for instance the Golden Gate Bridge and George Washington bridge are common examples of where these types of cables are used.  (3)
2. Parallel Strand Cables, Closed Construction - These types of cables are related to numerous pre-fabricated galvanised bridge strands. The cables are parallel and have contact with each other. Fillers like aluminium or wood are employed to make the cables to a spherical cross section. Then the entire cable is covered with wire for more safety.  (4)
3. Parallel Strand Cables, Open Construction - These cables have everything common with the previously mentioned ones, except for that, they are all laid parallel but they aren't in contact with each other. The strands over here are prefabricated galvanized strands, which are arranged in a rectangular shape.  (5)
4. Parallel Rope Cables, Open Construction—they are exactly similar to Parallel Strand Cables, excluding the fact that in place of Bridge Strand Galvanized Bridge Rope is used.  (6)
5. Single Rope or Single Strand Cables--These are used for small structures. 
MODERN SUSPENSION BRIDGES
Today suspension bridges are dominating the bridge construction industry, due to the reason of being mega projects and the toil of millions of workers across the globe. Therefore to in order to begin the mammoth project, many aspects need to be taken into consideration. A detailed explanation of the steps taken in planning, designing and constructing suspension bridges in general is explained below.
1. Raw Materials
The composition of suspension bridges usually contains many steel components. Some examples are the girders or trusses, and then it's made use in the saddles, where the cables are placed on top of suspension bridge towers. In addition, it's also used to be drawn into wires, as for the same diameter, a flexible bundle of steel wire has a higher strength when compared to a solid steel bar. When analyzing the advantages of the reason for using steel for making the girders is because it makes the deck more firm. When stretching into wires, it increases the tensile strength, which is the main reason why, steel cables are used to sustain the bridges. In Some suspension bridges, galvanization (zinc coating) of the steel wires that form cables occur. Furthermore, the majority suspension bridge towers are built of steel as well. Nevertheless, some have been built on reinforced concrete. Concrete is another form of raw material where its mainly used to make the deck or road way. 
There are many aspects that are required to be taken into account when designing a suspension bridge. Thus every suspension bridge needs to be designed separately. Firstly, the geology of the location gives an establishment for the towers and anchorages, avoiding areas which are prone to earthquakes. Secondly, when digging waters, the nature and depth of the water being bridged can affect the physical design of the bridge and also the choice of materials such as protective steel coatings. Freshwaters and current strengths are some examples. Moreover, when in negotiable waters, it's necessary to guard the towers from having collisions with ships. This can be done by building an island at the base. Also, when designing very long suspension bridges, the curvature of the earth needs to be taken into consideration. The towers of the New York Verrazano Narrows Bridges, for instance, are tall and stand apart, and are have a distance of 4.5 cm separate gap on top when compared to the bottom. 
3. DESIGN FACTORS
There are various factors to take into consideration when scheming a suspension bridge. Namely, the sag ratio, , the back stay slope, the camber and the cradle and flare and the design load. The figure below shows the suspension bridge design factors, and a detail explanation following. 
The length of the suspension bridge and stability is controlled by the sag. The sag ratio can vary from 5.0 to 16.6 percent. It is calculated by dividing the sag from the span length. A low sag ratio of the main cables means, the bridge is more vertically stabilized but it makes the cable stress quite high and anchorages need to be strong. A high sag ratio means the stress among the cables are very little and it thus lets the anchorages to be placed near the tower. 
It is defined as the vertical distance joining the top of the beam floor at the mid span and straight line perpendicularly drawn within the tower tops. When a suspension bridge is loaded, camber helps the deflection of the bridge. Camber should be equal to around 0.67 percent of the span length. 
The vertical difference ratio connecting the deadman and support tower of the main cable until the elevation difference among the deadman and the tower is known as the Backstay slope. The backstay angle and the main cable can be equal. If that is the case, then the stress would be the same on either sides of the tower. The ratio of backstay slope is normally 1:2.5 . 
CRADLE AND FLARE
Cradle and flare mainly involve in helping to steady a suspension bridge. The lateral distance from a straight line drawn between the support points of the towers to the midpoint of one of the main cables to is called cradle. The lateral distance from the anchorage to the cable support on the tower is called flare. Normally the cradle is equal to 1.25 % of half-span length. The flare is approximately between 2 and 3 % of the horizontal backstay length. 
There are many observations to look for, when designing loads for suspension bridges. The natural conditions of the construction site, the importance of a bridge, span length, and its function (vehicular or railway traffic). The dead load should be determined accurately when designing suspension bridges, as its one of the key forces on the main components on the of the bridge. Moreover, another important issue for long-span suspension bridges is protecting structural safety against strong winds and earthquakes. Taking wind into consideration, the vibrational and aerodynamic characteristics is very important. In the situation of earthquake, estimating the evaluation of energy and earthquake magnitude are crucial for bridges in regions prone to important events. In addition, design loads comprise of fabrication errors, and erection of members, possible movement of the supports and changes in temperature. 
4. ANALYTICAL METHODS
* Classical Methods
* Modern Design Methods
The classical methods can be classified into two sections, the elastic theory and the deflection theory. Both the theories are in-plane analyses for the global suspension bridge system. The entire suspension bridge is assumed a continuous body and the hanger ropes are closely spaced.
Both of these analytical methods assume:
* The cable is completely flexible.
* The stiffening girder is horizontal and straight.
* The geometric moment of inertia is constant.
* The dead load of the stiffening girder and the cables is uniform.
* The coordinates of the cable are parabolic.
* All dead loads are taken into cables.
The difference between the theories is whether cable deflection resulting from live load is considered. 
Modern Design Methods
Finite Deformation Method: With the development of the computer in recent years, the finite displacement method on framed structures has to be used as a more accurate analytical method. This method is used for plane analysis or space frame analysis of the entire suspension bridge structure. The frame analysis according to the finite displacement theory is performed by obtaining the relation between the force and the displacement at the ends of each element of the entire structural system. In this analytical method, the actual behaviour of the bridge such as elongation of the hanger ropes, which is disregarded in the deflection theory, can be considered. The suspension bridges with inclined hanger ropes, and bridges in the erection stage are also analysed by the theory. While the relation between force and displacement at the ends of the element is nonlinear in the finite displacement theory, the linearized finite deformation theory is used in the analysis of the eccentric vertical load and the out-of-plane analysis; because the geometric non linearity can be considered to be relatively small in those cases. 
Elastic Buckling and Vibration Analysis: Elastic buckling analysis is used to determine an effective buckling length that is needed in the design of the compression members, such as the main tower shafts. Vibration analysis is needed to determine the natural frequency and vibrational modes of the entire suspension bridge as part of the design of wind and seismic resistance. Both of these analyses are eigen value problems in the linearized finite deformation method for framed structures. 
5. STRUCTURAL ANALYSIS
* Stiffening Girders/ trusses: Longitudinal structures which support and distribute moving vehicle loads act as chords for the lateral system and secure the aero dynamic stability of the structure.
* Main Cables: A group of parallel wire bundled cables which support stiffening girders/trusses by hanger ropes and transfer loads to towers.
* Main Towers: Intermediate vertical structures which support main cables and transfer bridge loads to foundations.
* Anchorages: Massive concrete blocks which anchor main cables ans act as end supports of a bridge. 
Tension and Compression in the Structure
The tension forces are supplied to the cables supporting, which run among the two anchorages. The weight of the bridge and the load cause the cables to stretch exerting a tension force, as it goes from one anchorage to other. Thus, the anchorages also experience a tension. Nevertheless, since they are tightly held to the ground the force is scattered. This is the same scenario with the towers, which are also held firm. 
The suspension bridge deck is pushed by compression forces, however since it is a type of suspended roadway, these cables shift the compression forces to the tower, which spread the compression directly towards the earth, where they are deep-rooted. 
· MAIN TOWERS
a. Longitudinal Direction.
b. Transverse Direction.
Towers are classified into rigid, flexible, or locking types. Flexible towers are commonly used in long span suspension bridges, rigid towers for multi-span suspension bridges to provide enough stiffness to the bridge, and locking towers occasionally for relatively short-span suspension bridges. 
The towers are classified into portal or diagonally braced types. Moreover the tower shafts can either be vertical or inclined. Typically, the centre axis of inclined shafts coincides with the centreline of the cable at the top of the tower. Proper examination of the tower configuration is important, in that towers dominate the bridge aesthetics. 
· SUSPENSION CABLES
In early times, chains, eye-bar chains, or other material were used for the main cables of suspension bridges. The 19th century brought the use of wire cables, and parallel wire cables too. In 1883, cold drawn and galvanized steel wires were adopted for the first time. However, this type is used in almost all modern day long span suspension bridges. The type of parallel wire strands and stranded wire ropes typically comprise cables. Generally, strands are bundled into a circle to form one cable. Hanger ropes might be steel bars, steel rods, stranded wire ropes, parallel wire strands, and others. Stranded wire rope is most often in modern suspension bridges. There also some types of wire strands where its covered with polyethylene tubing. 
Parallel Wire Strands covered with Polyethylene tubing. (2)
· SUSPENDED STRUCTURES
Stiffening girders may be I - girders, trusses, and box girders. In some short span suspension bridges, the girders do not have enough stiffness themselves and are usually stiffened by ropes. In long span suspension bridges, trusses or box girders are typically adopted. I-girders become a disadvantage due to the aerodynamic stability, ease of construction, maintenance, and so on. 
In general, anchorage structure includes the foundation, anchor block, bent block, cable anchor frames, and protective housing. Anchorages are classified into gravity or tunnel anchorage system as shown in figure below. Gravity anchorage relies on the mass of teh anchorage itself to resist the tension of the cables. This type is routine in many suspension bridges. Tunnel anchorage takes the tension of the main cables directly into the ground. Adequate geotechnical conditions are required. 
6. CONSTRUCTION SEQUENCE
INVESTIGATION OF BASIC CONDITIONS
Number of spans
Continuity of stiffening girder
Type of suspenders
Design of members
Design procedure for the superstructure of a suspension bridge
Construction of a suspension bridge includes the chronological construction of the three major components: the towers and cable anchorages, the cables that support them, and finally the deck structure. These steps are explained in detail below.
* Firstly the formation of towers takes place. They are made by digging a suitably firm rock formation. Towers are built on dry land as well as in water. Construction of towers on dry land is very much feasible compared to water. Certain bridges are designed so that it's made on dry land. However, in order to build a tower in water, first the construction involves lowering a caisson to the ground below water, which is a cylinder made of steel and concrete. It behaves like a circular dam. The water is removed from the caisson interior, which lets the workers to excavate, in an area without water. Then, once the excavation is complete, a concrete tower base is made and poured into it. 
* Every bridge has its own ways of construction detailing. The Akashi kaikyo bridge for example, has each of the 2 steel towers consisting of 2 columns. The columns consist of 30 vertical blocks, each of which is 33ft high . Each block consists of three horizontal parts. A crane is placed connecting the columns and lifts three segments in to position on every column, and then finishing a layer. After the completion of a block on among every column, a crane called ‘ bootstrapping' crane is used. It lifts the segments of the next layer into position. Then, at suitable intervals, diagonal bracing is added within the columns. 
* The main tower does not have any cable support, thus can be hazardous when even low speed winds occur. It can cause oscillations. Hence, the vibrations can interrupt construction. A method of solving this problem is to lengthen the wire at the tower top, to the tips connected to weight and oil damper on the ground. 
Tower constructions that will stand in water begin with caissons ( a steel concrete cylinder that acts 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. The figure above illustrates this.
* Suspension bridge cables need to be supported and secured, otherwise the bridge will collapse. Therefore anchorages are made. They secure the ends of the cable. Anchorages are large blocks of concrete firmly connected to very strong rock structures. The building of anchorages involves, strong steel bars with circular ends (sometimes referred to as eyebars) are embedded in concrete. Opposite the anchorages, spray saddles are erected, which supports the cable at the place exactly where each and every bundles of wires separate. Hence, each wire bundle is secured to the anchorages eyebars.
Anchorages 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 cables eventual path, from one anchorage across the towers to the other anchorage.
* Once the completion of the towers and anchorages is done, a pilot line is strung beside the cables eventual path. It's put from one anchorage to another, across the towers. Positioning of the pilot line can be done using several methods. For example, helicopters can be used. Or boats take the line across and are lifted into the correct position. Once the pilot line is placed on its correct location, a catwalk is created, which is placed along the bridges whole length, which is around 1 metre beneath the pilot line. This is done so that labourers can attend the cable formation without hassle. 
* The next step would be spinning the cable. In order to start, a huge wire coil is placed at the anchorage. The wire's free end is circled in the region of a steel channel fastened onto an eyebar. It is known as a strand shoe as well. The wire is looped in between the strand shoe and the spool, in the region of a spinning wheel that is ascended on the pilot line. Then the wheel bears the wire from corner to corner of the bridges path, and at the other anchorage the wire is circled around a strand shoe. The wheel returns to the anchorage at the beginning , placing one more strand in position. The entire process is recurring till a bundle of the required amount of wire strand is made. The number can change depending on the bridge. Mostly varies from 125 strands to 400 plus. While the spinning is taking place, the labourers staying on the catwalk checks whether the wire loosens properly and freeing from any twists. As spools get exhausted, a continuous strand is formed by the splicing of the corner of the wire until the wire from the spool. In order to keep the wires together, as a thick bundle is formed, wire straps are placed at regular intervals. The extra wire impending off the spool is cut and securely placed at the anchorage. The same procedure continuous for the following bundles of wire.
The quantity of bundles required to form a complete cable differs from bridge to bridge. For example, the Golden Gate Bridge has 61, and Akashi kaikyo bridge has 290. In order to make the bundles into a compact cable, a special preparation using radially placed jacks is used. It compresses the bundles and then is wrapped around with steel wires. This is process is done after the proper number has been spun. At preset intervals steel clamps are mounted on the cables, to provide as anchoring locations for vertical cables, which bond the decking to the support cable. 
* The construction of the deck begins, when the vertical cables are connected to the primary support cable. The important thing of building the deck is that the forces need to be balanced every time, therefore the structure should be made in both directions at the correct rate, from the support towers. The main technique is using a moving crane which rolls over the main suspension cables and lifts the deck segments on the exact locations. Then the labourers attach the sections to the previously placed ones. They also join it onto the vertical cables, which suspend from the main suspension cable, lengthening the complete extent. On the other hand, the crane is able to rest exactly on the deck and go through placing each section. 
* The finishing stages of construction of a modern suspension bridge include, covering the deck structure with a base layer in the form of steel plates, and then cemented over. Furthermore, the steel plates are painted and for lighting, electric lines are installed. Moreover, ongoing maintenance procedures take place. As for instance, at the Golden Gate bridge, permanent staff of iron workers and painters still work on a daily basis, replacing corroded materials and other steel components, and painting touch ups too. 
7. BRIDGE SITES
The choice of a good bridge location is very important. There are certain aspects to chew over when shaping a bridge site. Some of these are the tower spacing, the work area and bridge clearance.
The tower spacing distance is made as short as possible, typically less than 400 feet. Also the towers are kept at the same altitude. For long spans, where there is a reasonable difference in elevation requires massive wire ropes plus it needs to increase problems regarding material-acquisition. Moreover, longer spans also can increase the tension in the cables, in need of much heavier towers and anchorages, and also increase the construction effort. In addition, difference in the tower and bank elevation should be minimal. 
BRIDGE CLEARANCE AND WORK AREAS
Due to cable sag, locations far above the ground from the towers are generally avoided, for adequate clearance. Sag based on probable loads are considered when determining clearance. In addition, selecting a fair level space just about each tower is crucial. For clearance reasons, usually an apt location would be a sharp slope passing the loading area. 
8. Comparison of Suspension Bridges
Advantages over other bridges
* Since its possible to construct at a greater height, even on water bodies, it allowes tall ships to pass through.
* It can economically span a very extensive canyon and waterway, by making the centre span very long in ratio to the amount of materials necessary.
* No need of access from beneath for building or temporary central supports, which allows the bridge to span a very turbulent waterway.
* The flexibility of the suspension bridges allow it to flex even under severe wind conditions and also seismic conditions, where rigid bridges would needed to be constructed stronger and heavier in order to withstand the conditions. 
Disadvantages over other bridges
* When going through major wind loading, the bridge's towers exert a great torque force towards the ground. Therefore if built on marshy land, its necessary for a very expensive groundwork.
* In response to concentrated loads, the flexibility is not always used for regional rail crossings, in which the maximum live load concentration is at the location of the locomotives.
* At times, when being too flexible and lacking stiffness, the suspension bridge can be unusable in turbulent weather, therefore needs to be temporarily shutdown to traffic. 
CASE STUDY - The Akashi Kaikyo Suspension Bridge
Japan's Akashi Kaikyo Suspension Bridge is hailed has the longest suspension bridge made by mankind. Many other countries across the world envy this dynamic beauty, which is truly a modern wonder. It is without doubt the country's most supreme engineering feat so far. The bridge took around 10 years to be completed, with the help of over 2 million workers. In addition, it is composed of approx. 1.4 million Cubic meters of concrete and 181000 tonnes of steel. It is also said that, the steel cable that is used, could circle the world 7 times, which proves the amount of hard labour gone into this mammoth project. The roadway contains 6 lanes and also connects the Awaji island and the Kobe mainland city, which is a distance of 4 miles. 
Like a usual suspension bridge, the Akashi Kaikyo bridge has more cables added, to prevent any collapsing of towers, cables and road way. They are held firmly at both ends at large anchor blocks, which weighs around 350000 tonnes. The two main towers are mounted on two massive spherical foundations, which consists of 265 000 cubic metres of concrete, and weighs 15 000 tonnes, with a height of 60 metres. The moulds for both foundations were done in dry dock. Nevertheless, the Japanese had a major concern, because they were dealing in water, and normal concrete doesn't mix with water. Therefore, they had to make a special kind of concrete which mixes with sea water without any problem. 
Construction Sequence of The Akashi Kaikyo Suspension Bridge
The Akashi Kaikyo Suspension bridge can be termed as a typical suspension bridge, however the technology used in construction was beyond limit. Below are general steps of how this feat was achieved.
Construction Technology of the Suspension Bridge Superstructure
The main tower of the Akashi kaikyo Bridge scaled great heights as it reached approximately 300 m above sea level. The construction of a tower of this magnitude, isn't an easy task, thus construction efficiency should be of high order. The factory equipment was improved and the number of cranes was also made better, which ensured that the weight of the blocks increased as well. Special machinery equipments such as creeping cranes were employed for building cranes because the scheduling will eventually become a problem if building cranes are prepared as the towers are very high and therefore the cranes will need to climb. Thus the special equipments which climb rails installed on tower pillars are used. The bridge exploited the use of a tower crane, which climbs and falls, a post away from the pillars. The crane is of high technology where it can self adjust the height in along with the pillars height, and even rotate completely. The main tower like any other suspension bridge does not have any cable support, therefore an installation of the TMD or Tuned Mass Dumper was used especially for the main tower, as shown in the figure below. 
The 1989 started the construction of both the towers. It is noted that the towers height has the same height of the Eiffel Tower in Paris, which is designed to have a 200 year life span. Both towers are around 283 metres tall and extra 60 metres taking the foundations into consideration, and each tower has 90 sections. Since the design allowed only twenty five millimetre offset at the top, the towers were constructed with supreme precision. This point of accuracy was accomplished by ‘surface ground' of each block to an exact finish. Approximately 700000 bolts were used in making the towers. Another specialty of the towers is that they are designed to flex in storm conditions. Moreover, they have special mechanisms where they counteract and dampen any movement. 
Following the typical construction procedure of a suspension bridge, once the towers were finished, the construction of the cables took place. A temporary cable was drawn out between the two towers and a wire mesh walkway was made for the labourers to start the construction of the main cable. The walkway is shown in the figure below. New low alloy steels were used in the Akashi Kaikyo Suspension Bridge, and it was strengthened with silicon. This was developed as it increases the tensile strength 12 percent more than all previous wire formations. Increase in the tensile strength brings about a resistance in pulling forces. Few suspension bridges use steel wires formed with galvanized cables i.e. coated with zinc. They used the equipment to pull the cables from tower to tower. The bridge implemented the PS method; however, the length of the cable became approx. 4000 metres, which was twice the previous length. The method is shown below (photo 7). This caused a doubt in the minds of the engineers whether the construction on-site was achievable and also would the quality of the parallel wire cable be assured. But, it wasn't long till a full size strand was examined and manufactured, wounded on a reel and confirmed that construction could progress. The pilot line is the important part of the cable stage as it connects all the spans. The erecting process happens with the sea crossing. This type of crossing was done from a method which uses floats that are joined to the line and pulled by a tug boat to a system when the rope is under tension by crane ships and tug boats. Its pulled from the sky and, it reduces the impact on the ships passing by. This wasn't a very notable system as the Akashi straits is and International route. So it carries very high volumes of traffic with ships. Such a system could perturb the transportation. Nevertheless, a new system was developed, which engaged the lifting of a light weight, very high strength synthetic fibre by a helicopter, usually larger than normal. Photo 7 shows the helicopter carrying the fibre. 
Stiffening girders or trusses have less hassle as they could be constructed without the going to the sea surface beneath. The type of truss was therefore adopted without problem. The procedure of construction includes the rigid coupling hinge construction method, which was later implemented in the construction of the Akashi kaikyo Bridge. In this system the newly made truss blocks are manufactured at the factory and coupled to active components on site. Also the hanger rope is pulled in to the new part and gets stabilized. Suspension bridges in the West use hinge construction methods but that is not feasible in wind, thus this system provides a superior wind resistant stability. In addition, this method of construction normally needs the hinges to take up the additional stress on the diagonal truss bracing and the hanger rope at the end of erection. A multiple joint came into play over here, where there is no rigid coupling due to the pulling tension of the joint. Furthermore, as used for the Akashi Kaikyo Bridge, the larger scale block construction method makes the stiffening girders fabricated as large blocks and is mounted by large scale crane ships to curtail construction period and relieve the completed tasks of the initial phase. The picture below shows the large block construction method for another bridge. 
It was the time for the deck or roadway to be made, after the completion of the main cables and vertical cables. The construction of the deck began in 1994. The concrete sections were carried by large cranes, with each section weighing 4000 tonnes, they consecutively were bolted to the right positions, around 290 sections for the entire deck of the bridge. That is surely one mammoth number. The fixing of the decks, segment by segment is shown below in the photo. The sections consist of a triangulated form, which indicates that even though the weight is minimum, each section is given a maximum strength.
September 1998 saw the completion stages of the deck, which meant the bridge was soon to be opened. Next year by the 5th of April, the Akashi Kaikyo Suspension Bridge was opened in grand style for the people of Japan. 
Some Major Technological Developments of the Akashi Kaikyo Bridge
Over the years bridge engineering has improved drastically in so many ways. Some of which could be seen in this dissertation. However, when it comes to the construction of suspension bridges, no matter how old, the sequence still remains the same. As time passes, and technology keeps improving day by day, the changes that take place in order to make better a living are worth a mention. Nowadays in bridge construction the amount of planning, designing and efforts put into these projects are remarkable. Mankind is able to finish quicker; labourers and engineers get paid better and the organization makes some profit as well, after the completion of these mammoth projects. Moreover, another change seen today's world is the availability of resources. Engineers are able to come up with some sort of a solution for most of the problems faced in construction and designing.
When going into detail a radical change is shown especially in the equipment and machinery that are used in the construction of the main towers, and the suspension cables. Today even massive helicopters are used to carry materials, such as girders or concrete. Creeper cranes are another form of improved cranes, where it can hang on the rails when constructing the main towers. And it is a well known fact that the future looks brighter as well, and there would be far more improvisations in the next few years.
Finally, in my opinion, I believe suspension bridges are by far the best type of bridges made by man today. As I have learnt from this dissertation, my knowledge has increased vastly from the beginning till the end, and I would love to be part of any suspension bridge project in future, as being part of a venture on these modern day wonders will truly be a memorable experience.
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