The Clifton Suspension Bridge
FunctionThe Clifton Suspension Bridge was designed by Isambard Kingdom Brunel and completed in 1864. The span spans 214m across the Avon Valley Gorge from Clifton to Leigh forests as shown in figure 3. The towers are 26.2m high and the span concatenation has a breadth of 6.1m Centres to center. There are two vehicle lanes and two prosaic waies. The prosaic paseo is to boot used as a sing topographic point along the Avon gorge. There are about 10,000 autos traversing per twenty-four hours with a gross vehicle weight bound of four dozenss. The toll for the span is presently 50p ( 27/11/09 ) . Bing an historic span, the construction requires changeless services which the tolls fund. bestcustomwriting.com review The velocity bound on the span is presently 15mph and the weight bound is controlled utilizing a modern weight beam ( Mitchell-Baker, D. Et al 1988 ) . The span was designed to originally take the weight of Equus caballuss and passenger cars. The site location was chosen because of its short and flat span.StructureThe span takes the signifier of a convention suspension span. This signifier was ambitious at the clip of design and if it was completed on agenda it would hold been the longest suspension span in the universe. The suspension span was a suited pick for two chief grounds. The first ground is that the tallness between the deck and the river below is 75m and to build a tower would be expensive. It besides would hold been expensive to build any signifier work. A suspension span can be constructed without the assistance of signifier work and Brunel â€˜s design did non necessitate a tower compared with Telford proposal which included two Gothics styled towers ( Moore, Fuller. 1999 ) . The 2nd ground is that the strength of the environing topography allowed the being of ground tackles. In state of affairss where a suspension span would be suited, the status of the land is unsuitable for bearing the force per unit area from the overseas telegrams. One of the disadvantage of utilizing a suspension span on the site is that it can merely be a individual span. The ground tackles have to take the entire tenseness of the concatenation compared with a three span span where the deck on the side span acts as a counter weight, alleviating tenseness in the ground tackle. The construction is formed chiefly of a long concatenation, similar to a motorcycle concatenation, two towers and the span deck. As it is shown in figure 5 the concatenation is formed of three sub-layers on each side, each bed dwelling of an jumping 10 and 11 level wrought Fe bars. By increasing the figure of concatenation beds the overall opportunity of prostration lessenings. The level wrought Fe bars were designed to be every bit long as operable. The long bars decrease the entire weight of the ironss by cut downing the sum of heavy articulations. . By increasing the sum of ironss, the construction becomes less reliant on each person concatenation ; hence failure of a concatenation should non take to prostration. The dip to cross ration of the ironss contribute to the efficiency of the construction. High span to depth ratios cause high tenseness in the concatenation, this is because of the way of the concatenation reacts about perpendicular to the weight, making an inefficient construction. Low span to depth ratios do a more efficient concatenation but the tallness of the towers have to increase hence increasing the cost. The most effectual span to depth ratio is about 1:10 which is what was adopted by Brunel for the span. This is an betterment to the 1:13.5 ratio which Telford antecedently adopted on the Menai span. The chief catenary ironss are non attached straight to the deck at mid span ; this is done to let the chief deck to hover freely in the air current without seting strain on the ironss ( Pugsley, Sir A. 1976 ) , ( Porter G. 1974 ) . Hanging at 8ft intervals are the shaped Fe rods, which transfer the burden onto the concatenation. The array of rods is designed to oppose prostration if a individual rod should neglect. The rods are attached slackly between the concatenation and longitudinal girder, see figure 5 ; this allows motion which decreases the opportunity of failure from span motion. This so imposes a perpendicular downward force onto the towers and tenseness along the concatenation and in the ground tackles. The longitudinal girder as shown in figure 5, is a uninterrupted stiffened I beam. The girder is 3ft deep and connects the cross girder to the rods. The original design proposed by Brunel used a timber lattice girder with a matching stiffness, but by the clip of the Bridgess building the lumber lattice was replaced by an Fe plated girder. The girder takes the emphasis applied to a individual articulation on the concatenation and traverses it along the longitudinal length of the concatenation. As illustrated in figure 4, a truss construction is adopted for the cross girders. The truss construction is a really strong and efficient construction along the length. The shallow deepness allows thin strips to organize the trusses without clasping. The place of the cross girder is shown in figure 5. The cross girders are braced horizontally utilizing thin Fe strips to respond against air current burden. The quadrangle form deforms under burden by rotary motion at the articulations. The brace forms a triangular molded construction ; distortion in the triangular molded construction occurs by flexing of each member, therefore increasing the elements stiffness. Live tonss are transferred onto the lumber beams which span between each cross girder ; using a perpendicular burden and doing a bending minute in the girder. The lumber decking was chosen because it was light and suitably strong ; it besides allows easy accessible fixs. A shaped Fe adorning frame was added by Barlow and Hawkshaw to increase rigidness. The saddles are situated on top of the towers. The saddles allow sidelong motion of the ironss. Lateral motion occurs due to temperature alterations or unsymmetrical burden. The saddles besides allow the perpendicular emphasis to be reduced in the rock tower by increasing the contact country, understating the hazard of oppressing the rock. The ground tackles are 17m below the land and the ironss are spread into a chamber to make a stable foundation. The spreading of the concatenation allows the tenseness to be opposed by the compaction of the drop, non entirely trusting on the clash. The advantage of this is that the strength of the ground tackles increases ; it besides takes advantage of the strong limestone foundation. ( Pugsley, A. 1976. )StrengthThe constructions weight bound for vehicles is presently four dozenss. This weight bound was introduced about 50 old ages ago when applied scientists decided that the big tonss and weariness could take to fall in. The sum of vehicles on the span at one clip is controlled by the toll booths. This is done to cut down the entire burden on the span at any minute. Brunel designed the span to defy an adventitious burden of 100lbf/sq.ft which is about equal to 4.7 KPa of force per unit area ( Porter G, R.F.D. 1974 ) . . This is simular to the unrecorded burden which is adopted on modern Bridgess with similar spans ( Bangash, M, Y, H. 1999 )ConstructionAfter planing the span, the foundations and abutments were the first elements to be constructed. Then the towers were the following thing to be constructed. The ironss were pulled across by rope and so the deck was attached to the concatenation.CareBetween 1864 and 1953 the lumber decking had been replaced three times and the ironwork had been treated twice and at the terminal of this period was still in good status. Two suspender rods had failed in a terrible storm in 1877 and three more had failed in 1887. Both occasions the exact cause of the failure is still non convincingly known. In 1861 a 6 metric ton vehicle weight bound was appointed to the span. The size and weight of vehicles was continuously increasing and applied scientists were concerned with the Bridgess construction. It was based on the theory that repeated lading on metal causes its hempen construction to go crystallite. In 1918 one every 10 bolts from the rods were removed for proving, and they were all found to be of equal strength though some cleft appeared ; these clefts were likely to happen from hammering. The drainage of the span had caused serious corrosion to anchor degree ironss. In 1925 an excess nexus was added to the ironss but there were still concerns for the ground tackles status. To get the better of this concern concrete was poured to a deepness of above 9ft above the ground tackle. In 1953 the duty of the span was passed to the trusses and the national heritage. The point burden of wheels was known to be more detrimental to the deck than to the construction as a whole, doing the deck to be once more in a terrible status. The weight bound was so changed from 6 ton bound to 2.5 ton axle weight and 4 ton vehicle weight. ( Mitchell-Baker, D. . Cullimore, M. S. G. 1988 ) In 2009 a prosaic noticed a serious cleft in one of the suspension rods and the closing of the span followed. Impermanent supports were put in topographic point while the rod was replaced. A twelvemonth earlier work to better the sealing, drainage and new route surface was completed. This would diminish the sum of corrosion of the Fe work. ( BBC News. 2009 )AestheticssThe span is really aesthetically delighting, it has few single elements, and each component is similar in map. The girders are really thin and it has a uninterrupted span which besides makes it more appealing to people, most people would hold the span is beautiful. The form of the construction besides reflects the force applied to it, being dilutant in the center and thicker as it gets towards the borders where the greater minutes would happen. The span besides has a bold and dramatic lineation when viewed from along the vale ( Gottermoeller, F. 1998 ) . The towers are curved so that they appear tall from below, organizing a bold construction. The towers are besides in good proportions compared with the immediate surrounding and harmonious in three dimensions. The span is constructed utilizing locally sourced stuffs, incorporating the construction into the environment. ( Chen, W et Al. 1999 ) . The span is 3ft higher on the Clifton side. This is done to halt the semblance that the span deck is falling towards the drop.
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