Structural Components Of Suspension Bridge Engineering Essay

Structural Comp superstarnts Of rest period Bridge Engineering EssayINTRODUCTION hanging twain is a role of tide over in which the road way or the underprice is hang up below the break of serve business lines. It is a simple(a)st form of connect which was do of lot and wood in olden days. The advance(a) shift couple highly-developed was in 19th century. In those tie the transmission linegrams be carried by development vertical suspender. The 2 ends of the product lines argon suspended on hovers. The pack of the tie is transferred to the anchorage system by cables. The anchorage is fixed firm on concrete blocks or solid rocks .In order to distribute the core evenly and besides to protect the cables from breaking, the cables ar spread over a galactic area inside the anchorage.Historical Back endIn advance(prenominal) times human beings open up it very clownish to featherbed the well out and a deep gorge to survive. A successful solution found out by early people was to drop a corner between the twain banks of the deep flowing stream. This results in the idea of simple beam link up in early times. Early bridges were do of post and lintel structures, stones or timber or the combination of the both. subsequent on the social function of bamboo or simple rope gave rise to the schooling of rope suspension system bridge. Central and South America and are the offset to use rope suspension bridge.stock-photo-rope-bridge-suspension-bridge-35093119.jpgFigure1 ROPE hanging BRIDGELater on the concatenation cables were developed when the wrought iron bars became locally available. The firstly bridge constructed victimisation chain cables were throng Finleys in West muchland country, Pennsylvania in 1801.In early British chain bridges the nonable one was Menai bridge with 176m payablette. One of the pertinaciousest parbolic emission chain was Clifton Suspension bridge.menai-bridge.jpgFigure 2 MENAI BRIDGEclifton-suspensio n-bridge-bristol-gben440.jpgFigure3 CLIFTON break of serve BRIDGEAfter the chain cable the cable-cable was developed. Foot bridge at falls of Schuylkill was the first equip-cable suspension cable developed in 1861.The first major bridge constructed using modern methods was Joseph Chaley Grand Pont Suspendu across in Fribourg across the Sarine valley .Its verbalism was immaculate in 1834.The first major wire-cable in USA was the Wire bridge at Fairmount in Philadelphia , Pennsylvania, embroil of 109m and the construction was completed during 1842. A notable bridge was Niagara bridge with250m twain in 1855.Later on the Ameri derriere Engineers was constructing Suspension Bridge with high span continuance. The notable one among them was are Ambassadar bridge in Detroit with 564m span in 1927, George Washington Bridge in New York with 1006m span in 1931 and Golden Gate Bridge in San Francisco in 1937.Among the parallel wire cables the Otto Beit bridge outside USA was the firs t Suspension bridge constructed with modern techniques.golden_gate.jpgFigure 4 GOLDEN GATE BRIDGESTRUCTURAL COMPONENTS OF suspension system BRIDGEFigure 5 Structural Components of Suspension bridgeThe in a high place figure shows the structural components of a third span Suspension bridge. The dissimilar parts of a suspension bridge areMain Cables which contribute the aggrandize and transfer the loadings to the leap outing main(prenominal)stay and anchorages.Deck suspended from the principal(prenominal) cables.Towers to support the briny cables.Hangers which is use to connect main cables and deckAnchorages to which the ends of the main cables are connected to protect it against both movements.1. CABLESThe main function of cables is to support the deck which carries the traffic loadings and to transfer these traffic loadings to the prevails and anchorages by direct tautness pressures. Cables are shake up of high efficiency steel wires. The tensile military unit of t he wire is 1550N/mm2. The cables of the Akashi Kaikyo bridge in Japan is do of wires having high effectiveness with minimum tensile strength of 1800 N/mm2.The steel rods from which the wires are make are having higher carbon content. The wire with high tensile strength is obtained by cold drawing the wire. After the final drawing the wire is galvanized for corrosion protection.301678.jpgFigure 6 AKASHI KAIKYO BRIDGEDifferent types of cablesa. curlicue Bridge StrandsSpiral bridge marges are manufactured by winding several form of round steel wires in a helical experimental condition onto a p to each oney centre core wire. When layers of wire are laid it should be made sure that an opposite helix to the preceding layer should be laid. Due to twisting of wires spiral strands gets self-compacted under axial loading. As a result of this when the strand is first loaded, non springy str and so on come ups. So in order that the strand should behave elastically, the twisting of wir e should be avoided during manufacture. Examples of bridges that have used spiral bridge strand areTancarville bridge (france) with span length 608m, Cable size of it is 56no, diam of strand is 72mm.Constuction was completed during 1959Lillebaelt bridge (Denmark) with span length 600m, Cable size 55no, Diameter of strand is 68.7mm and 6no 41.4mm diameter strands. Construction was completed during 1969.Figure 7 Spiral bridge Strandb.Locked Coil StrandLocked pealing strands is manufactured in the comparable way as the spiral strands is manufactured. The only difference between the ii is that in locked coil strand the final layer of wires are made up of interlocking Z-shaped wires. As a result of this proportion of the cross sectional area of strand to wire area increases, also a smooth exterior surface is obtained .Examples of bridges that have used Locked coil strands areTamar bridge (UK) with span length 335m cable size 31no, Diameter of strand is 60mm.Construction was complet ed during 1961.Rodenkirchan bridge (Germany) with span length 378m, Cable size 37no, Diameter of strand is 69mm.Construction was completed during 1954.Askay bridge (Norway) with span length 850m, Cables size 21no, Diameter of strand is 99mm.Construction is completed during 1993.There are two types of arrangements that can be provided for spiral strands and locked coil strands. One of them is close packed hexangular formation which has the returns that the cross-section can be circularized when aluminium or plastic spacer are added and then wrapped properly against corrosion. The other one is an open orthogonal array which is rarely used and doesnot have any wrapping operation as in closed packed hexagonal formation. The cable bands are simple fabricated structure. The disadvantage of open rectangular array is that on increasing wind load on the cable it is difficult to conduct inspection and maintenance on the inner strands.c. reduplicate wire cableIn parallel wire cables, severa l singular wire over the whole cable length is laid straight and parallel. It is constructed in two slipway, by aerial insitu spinning of the wires or by prefabricated parallel wire strands.Insitu span cables The aerial spinning method was developed during the 19th century and it was mostly used in unyielding span suspension bridge. In this method using the spinning wheel two or four loops of wire are pulled from one anchorage to the other. During each movement of the wheel, required sag is provided to the wire and the cables are assembled.Prefabricated parallel wire bands In prefabricated parallel wire strands bundles of wires are bound together by keeping plastic tapes at intervals and are prefabricated into hexagonal shaped strands. At each end sockets are fitted. The Akashi kaikyo bridge was the first bridge to use the longest prefabricated parallel wire strands with 127 wire strands, with average strand length of 4073m.2. DECKThe main function of deck is to support the load . The deck is suspended on the main cables by using vertical hangers. The most cockeyeding(a) load that the deck has to carry is the traffic loadings. The self weight of deck should be low because the deck is carried by the cables. Stiffening girders should be provided in the deck to transfer the loads from the deck to hanger.3.TOWERSThe main function of tower is to support the main cable. The ends of the main cable is connected to the tower which at a sufficient height to provide cable sag. Tower also support the laidification girder and side span. The initial loadings on the tower impart be the vertical load playacting at the top of the tower, utilise by the main cables, together with the loads acting on cable and bridge deck due to wind load and load acting on stiffening girder. Flexible fixed base are provided for the tower and cable saddles are fixed on the top of the tower. Due to this type of arrangement any movement in the cable saddle due to varying load will result in the longitudinal deviation of the tower legs4.HANGERSThe main function of hangers is to connect the bridge deck and stiffening girder to the main cables .Vertical hangers are used with equal intervals along the span. Based on using one or two parts of rope, thither are two types of hangers.Two part hangersTwo part hanger was used in long span suspension bridges. In this type of hanger the arrangement is in such way that over the main cables the hanger is drapped which is located in the wrinkle of corresponding cable band. Using sockets the bottom ends of the two rope of the hanger are connected to the deck. Hangers are usually made of steel wire ropeSingle part hangersSingle part hangers ends on the underneath of the cable and it is connected to the lower part of the corresponding cable band by a socket and pin connections. The lower end of the hanger is connected to the deck using simple bearing socket. This type of hanger is made up of spiral strand or parallel wires5.ANCHORA GESThe main function of anchorage is to support the ends of the main cable and to prevents any movements in the main cable by transferring the strength from the main cable to the ground. Since the anchorage has to resist a large force the fancy of anchorages is very tough unless the ground on which the anchorage is to be positioned is good and also if sound rock is available in the ground.Avantages and Disadvantages of Suspension bridgesAvantages1.When compared to other bridges, higher spans can be provided for the main span in suspension bridge.2. Construction cost can be cut down in Suspension bridge due to less material used when compared to other bridges3. No access is required below during construction of suspension bridge when compared to other bridges. Only for the installation of initial unstable cables the access is required.4.Suspension bridge can prevent earthquake movements than other bridges.5. Suspension bridge can be constructed at heights above the waterways to allow in the passage of tall ships.DisadvantageBridge deck vibrating due to laborious wind is prevented using aero projectile profiling.The deck ungracefulness of suspension bridge when compared to other bridges is very low. Due to this it makes the bridge very difficult to carry heavy rail traffic.The installation work is costly and requires more area to combat the effect of heavy load on foundation towers ,when Suspension bridge is constructed on soft ground.NON LINEAR ANALYSIS OF SUSPENSION BRIDGESuspension bridges was considered as the most efficient and unprecedented in architectural appearance when compared to other structural systems. But suspension bridge has more tendency to get deformed due to the unsymmetric loadings. This kind of switching is called as kinematical diaplacements. There are many ways to reduce the kinematical displacements in suspension bridges. One of the method is, if pliant cables are used in suspension bridges the local bending stiffness is take n into account while analyzing the stress-strain state. Other method to reduce kinematical displacement is to use rigid cables instead of tensile cables. Standard hot rolling or welded sections are used to make the structural elements. Also by using rigid cables it provides the required stiffness for the suspension bridge. The technique is not accurate but can be used or rough calculation.For analysing the suspension bridge made of flexible cables or rigid cables there are some numerical methods. The analysis of suspension bridge made of flexible cable is very difficult when the non-linear behavior is concerned. So it is canvas based on the assumption that the main cables are made of flexible cables ,when only doomed load is acting on the bridge its shape is parabola, all other structural elements are made of ideally elastic material, through out the span of the bridge the bending stiffness of the girder is off-key to be constant, the displacements in the hanger is neglected and the load acting on the cable is considered to be uniform. The loading is in such a way that dead load acts on the cable, the stiffening girder and cable supports the live load. By using these assumption the non-linear analysis is done using certain equations.But while analysisng suspension cables with rigid cables these assumptions are not applicable. In rigid cables there is incessantly some bending stiffness.Also the cables are made up of cadence welded or steel sections for the suspension bridge to be initially a stabilized. Grigorjevaet al. (2006) proposed a technique for the analysis of suspension bridge with rigid cables.CASE trainDynamic Response of the Suspension Span of the SAN FRANSICO-OAKLAND BAY BRIDGEThe dynamic seismic analysis of the suspension span of San Fransico-Oakland verbalise bridge was modelled to make a theatre on the effects on suspension bridge due to ground enquirys. Due to the combined effect of motions due to tectonic displacements and seismic waves ,ground motions are developed near-fault regions for along period. In olden days the seismic design codes for the structures were used based on the past experiences and the historical ground motion instrument and signal processing methods were not accurate.So it was very difficult to notice the ground motions. But the development of Modern broad-band, digital instruments helped in measuring rod the near-fault motions.The effect of long period motion is different for flexible and rigid structures. Rigid bodies will have a natural frequency higher than 0.2Hz and for longer wavelength seismic waves it behaves as a rigid body. But for flexible bodies the natural frequency will be low.Using a finite-element molding software the structure is modeled.The deck model is a combination of truss,membrane and reign over stiffness elements.The steel braced tower is represented by reference bending elements and the bridge cable is represented by tension-only cable element.The advantage of mo delling the structure in this way helps to reduce the degree of granting immunity which is an essential aspect in the repose of suspension bridge. After the sedateness initialization is completed as described in detil by McCallen and Astaneh,2000 ,the lucid integration scheme for non-linear analysis of earthquake motion is done. The ground motions in the near by areas will be affected by unhomogeneous reasons like the superposition of seismic waves, site geological answer etc. The effect of these parameters may vary for different ruptures happening in future day and these rupture may cause changes displacement in ground, velocities and accelarations.In this study the effect of rupture and wave propagation were studied by providing a parallel and finite difference in computational simulation of the rupture,a three dimensional finite difference calculation, empirical Green function and at seven points in San Fransico-Oakland Bay Bridge the ground motion is computed. By doing the above said it was found out that the far field in the near source can result in fault with periods of 0.2 to 0.5s due to directivity effects and the near field arrivals can result in fault with periods of 0.2 to 0.1 s due to tectonic movements. There are chances for these long period arrivals to accur along with the future earthquakes along the Hayward or San Andreas faults which is nearby San Franciso-Oakland bay Bridge and it will affect the long span bridges in San Fransico bridge. Along the Hayward fault ,five locations along the suspension span of western San Fransico two rupture model were synthesized for a ground motion of Mw =7.25.These were considered as mean and other one as standard deviation models.They were represented as HAY06 and HAY31.The ground displacements at the bridge generated was greater for the mean fault than the standard deviation but the standard deviation produced more acceleration and long durations.Analysis of the model has shown that the mean model pr oduced more stress than the standard deviation. The response of Bay bridge is computed against the ground motion from the rupture model HAY06.Due to this displacements occur which indicates that the flexible deck cannot respond as fast as the towers when large displacement occurs. The tower motion lags and then the deck starts to respond when the tower returns with the ground.