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 The bridge consists of twobridge towers tied together at the upper level by two horizontal walkways,designed to withstand the horizontal tension forces exerted by the suspendedsections of the bridge on the landward sides of the towers. The verticalcomponents of the forces in the suspended sections and the vertical reactionsof the two walkways are carried by the two robust towers. The bascule pivotsand operating machinery are housed in the base of each tower.

Tower Bridge – Bascule   However, there are other bridgedesigns that are still being used and there are still some very iconic bridgesaround the world which were constructed with different designs.·        Quicker to construct·        Easier to construct·        Reliability·        CostMost of the bridges in theworld are constructed with the designs mentioned above in this report, thiscould be for several reasons;Other Bridge Designs  The mono design uses a single cable from its towers and is one of the lesser-used examples of the class. In the harp or parallel design, the cables are nearly parallel so that the height of their attachment to the tower is proportional to the distance from the tower to their mounting on the deck. In the fan design, the cables all connect to or pass over the top of the towers. The fan design is structurally superior with a minimum moment applied to the towers, but, for practical reasons, the modified fan (also called the semi-fan) is preferred, especially where many cables are necessary. In the modified fan arrangement, the cables terminate near to the top of the tower but are spaced from each other sufficiently to allow better termination, improved environmental protection, and good access to individual cables for maintenance. In the star design, another relatively rare design, the cables are spaced apart on the tower, like the harp design, but connect to one point or several closely spaced points on the deckThere are four major classes ofrigging on cable-stayed bridges: mono,harp, fan, and star.

Cable-stayed bridges have been knownsince the 16th century and used widely since the 19th. Early examples oftencombined features from both the cable-stayed and suspension designs, includingthe famous Brooklyn Bridge. The design fell from favor through the 20th centuryas larger gaps were bridged using pure suspension designs, and shorter onesusing various systems built of reinforced concrete. It once again rose toprominence in the later 20th century when the combination of new materials,larger construction machinery, and the need to replace older bridges alllowered the relative price of these designs.A cable-stayed bridge has a single tower, sometimes more than one, fromthese towers cables support the bridge deck.

A standout feature are the cableswhich run directly from the tower to the deck, normally forming a fan or harp-likepattern or a series of straight lines that run parallel. They have somesimilarities to the suspension bridge, where the cables that support the deckare suspended vertically from the main cable, anchored at both ends of thebridge and running between the towers. The cable-stayed bridge is optimal forspans longer than cantilever bridges and shorter than suspension bridges. Thisis the range where cantilever bridges would rapidly grow heavier if the spanwere lengthened, while suspension bridge cabling would not be more economicalif the span were shortened.2,6        Cable Stayed Bridges One of the worlds most famous bridgesand most photographed bridge is The GoldenGate Bridge which is a suspension bridge spanning the Golden Gate on theWest Coast of the United States of America. This bridge is one-mile-wide and connectsSan Francisco Bay to Marin CountySuspension bridges are generally constructedto link land that is separated by a large body of water, they allow for peopleto commute and travel, saving time in the process. Roads and footpaths can beplaced on the deck of the bridge at the same time.

The cables used to suspend the deckmust be anchored at each end of the bridge, these main cables transform anyload applied to the bridge through a tension in the cables. The main cables don’tstop at the supporting pillars. They continue beyond the pillars to deck-levelsupports, and then onto connections with anchors in the ground which preventsthe cables from becoming too slack or loose. The deck or roadway is supportedby vertical suspender rods and/or cables which are called hangers.

Depending onthe location of the bride, the towers may sit on a canyon or valley edge wherethe road may proceed directly to the main span, if this is not the case thenthe bridge will usually have two smaller spans which run between either pair ofpillars and the connecting road which may be supported by suspender cables.Suspension Bridges get that name fromthe cables suspended between towers, and also the vertical suspender cables that take the weightof the deck below, upon which pedestrians and also traffic cross. This sort ofarrangement allows for the deck to be level or in some cases to arc upwardstowards the middle pf the bridge deck for additional clearance. The suspension bridge is a type of bridge in which the load-bearingportion (the deck) is suspended underneath cables on vertical suspenders. Like manyof the modern bridge designs one of the first examples of this bridge design wasbuilt in the early 19th century during the industrial revolution. 2,5        SuspensionBridge                 The Forth Bridge pictured above boasts three doublecantilevers and is a World Heritage site       situatedin Scotland. The bridge serves its purpose as a railway bridge which connectstwo   villages, North and SouthQueensferry                                          This image was taken from            The cantilever bridge became a popularbridge to construct due to their being a high demand for bridges that couldspan longer distances.

The main use for these bridges in to allow transport topass over such as trains and cars. Shortening travel time and distance.Cantileverbridges are bridges built using cantilevers, cantilevers are thestructures that project horizontally into space, with only one end supported.the cantilevers may be simple steel beams whereas the larger cantilever bridgeswhich are designed to handle road or rail traffic use a truss structure builtfrom structural steel, or box girders which are made from prestressed concrete.

The steel truss cantilever bridge was a huge engineering breakthrough when itwas first constructed, as it can span distances of over 460 metres and can besimply constructed at difficult crossings as there was very little falseworkneeded.2.4        Cantilever Bridge      This is a bridge whose load-bearingsuperstructure is composed of something called a truss, a structure composed ofconnected elements which often form triangular units.

The connected elementsthat tend to be straight may be stressed from tension or compression. In termsof modern bridges, truss bridges have been around for a long time and once theindustrial revolution came about, materials like wood and iron were being usedto make structures. Before the industrial revolution bridges where commonlyonly constructed making stone but iron and wood allowed architects to designstronger and more reliable structures. Truss bridges have always been known fortheir basic designs and are economical to construct due to the efficient use ofmaterials.2.3        Truss Underload, the top surface of the beams is pushed down or compressed at the sametime, the bottom edge is stretched or placed under tension.

Thesebridges are the simplest form of bridge. Early examples of a beam bridge wereconstructed using just a log that was placed across a stream, however, todaysexamples are made using large steel girders and can be constructed in differentways.Stiffness is the key to the construction of a beam bridge as it needs to resisttwisting and bending under load.

In its most basic form, a beam bridge consists of a straight horizontal beamthat is supported by piers at each end. The weight of the beam pushes straightdown on the piers. 2.2        Beam Ratherthan pushing directly down, an arch bridges load is carried outward along thecurve of the arch to the supports at each end.

This results in the transfer ofweight to the supports at either end. These supports, called the abutments havea sole purpose to carry the load and keep the ends of the bridge fromcollapsing or spreading out.Thistype of bridge is one of the oldest types of bridges and they have been aroundfor centuries. Arch bridges are known for their great natural strength and wereoriginally constructed using stone or brick, but todays arch bridges are builtusing reinforced concrete or steel thus allowing arch bridges to be longer withlower spans due to the newer materials being stronger and more durable.2.1        Arch There are 7 different types ofbridges, Arch, Beam, Truss, Cantilever, Suspension and Cable-stayed.    This corbel arch bridge was built out of cyclopeanstones and was built with the sole purpose of being able to allow chariots topass over the small valley.

Thestructure is 22 metres long, 5.60 metres wide at the base and 4 metres high. Makingit a relatively small bridge in comparison to some of the Goliath Size bridgeswe see today. The width of the roadway atop is about 2.50 metres and was justwide enough to allow chariots to pass over.

This being the main mode of transportat the time when the bridge was constructed. This bridge shows just how long abridge can last and it also shows us that bridges have been important to humansfor centuries. Having done some research intothe types of bridges I have found that there are 7 main bridge types. Allvarying in shape, structure, size and all of them built to serve differentpurposes in different situations. These bridge types are the most commonly usedand are still constructed all around the world using different materials.Bridges that you see and use almost every day are designed by very skilledarchitects and built with precision and accuracy by only the best engineers.

The time, money and work that goes into making a bridge is unprecedented. Fromarchitects to engineers, the design and construction of a bridge can takemonths, years and in some cases decades but that is nothing in comparison tohow long these bridges are designed to last. One of the oldest bridges thatexists and is still in use is The Arkadiko Bridge also known asThe Kazarma Bridge which can bedated back to somewhere between 1300 and 1190 BC in the Greek Bronze Age. 3.    Thedifferent types of bridge A bridge is a structure built to spanobstacles allowing for space underneath for roads, valleys or stretches ofwater to allow passage over the obstacle underneath. There are several designsthat each serve a specific purpose and are built with different situations inmind.

Bridges are designed around certain variables, whether it be the terrain onwhich the bridge is being built, the location of the bridges anchor(s), whatmaterial is being used to build the bridge, and the overall funding of thebridge. 2.    Whatis a bridge  The aim of this report is to writecomprehensively about bridges, the different types of bridges and the purposeof all the different types of bridges. Bridges are designed with certainpurposes in mind, from one extreme to the other. From carrying heavy loads tocarrying lighter loads. Other bridges are built to allow ships and/or othervehicles to pass under them.

This will be explained within the report. 1.    Myintroduction into my report on Bridges 

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