CABLE STAYED BRIDGES

Presented By: CHINTAN R PATEL Roll No. : 11CME13 EN No. :110410720010 M.E. Civil 3rd sem

IntroductionConsists of one or more pylonsCables supports bridge deckElegant, economical & efficient structureHighly cost-effective for short & medium span

Components

History of development:First cable bridge was of timber designed by C.T.Loescher in 1784 Many early suspension bridges were of hybrid suspension & cable-stayed construction.The 1st cable-stayed bridge of modern time was with steel decks.

The idea of using cable-stays to support a bridge has been around for a while, it was first applied in the 1800s in England (incorporated with suspension bridges), many of which had failed due to insufficient resistance to wind pressure (but also failure of the designer, and failure to understand the mechanics of such a bridge.)

But in the 1900s, several factors contributed to successful implementations:Better methods of structural analysis of statically indeterminate structures (via computers)Development of orthotropic steel decksHigh strength steels, new methods of fabrication and erection.

First concrete-stayed bridge , 1952

Why We Require Cable-stayed ?-The cable-stay design is optimum within cantilever bridges & suspension bridges.-Within this range suspension bridge will require more steel while cantilever bridge will require more material.

Types:(according to cable arrangement)Radial : cables connect evenly throughout the deck, but all converge on the top of the pierHarp : cables are parallel, and evenly spaced along the deck and the pierFan : a combination of radial and harp types Star-shaped : cables are connected to two opposite points on the pier

Quick points to be made:Buying different size cables for the radial bridge may or may not reduce the total cost compared to harp bridge (because you can buy in bulk) so the fan bridge is a structural and economic compromise.

The star shaped bridge only may have asthetic value; it is structurally flawed.

Types:(according to shape)(1)Side-spar cable-stayed bridge -cables are only on one side -useful for curved bridge -bridge exerts considerable overturning force upon its foundation and the spar must resist the bending caused by cables, as cables are on one side only.

(2)Multiple cable-stay bridge -2 to 3 span structure -structure is less stiff, creates difficulties both in construction & design of deck & pylon.(3)Cantilever spar cable-stay bridge -modern modification of bridge -reduces overturning force

(4)Extra dosed bridge -is a bridge with more sustainable bridge deck that being stiffer & stronger. -cable can be omitted close to the tower

(5)Cable-stayed cradle stayed bridge -it eliminates anchorages of pylons. -each epoxy-coated steel is carried inside cradle in a steel tube.

CABLE BRIDGEConnect the deck directly.

Not requires firm anchorages from ground.Construction is faster.Design is simple.Requires less cable.

SUSPENSIONConnect the deck with large suspension cables dropped towards deck.Anchorage from ground is necessary.Comparatively slower.Design is not simple.Requires more cables.

Tension and Compression Important!The tower is responsible for absorbing and dealing with compression forcesTension occurs along the cable linesThis works because a moving load is not applied evenly across the bridge, and as it moves one set or the other of the diagonals will find itself in tension

Key advantages:Much stiffness which reduces deformation of deck under L.L.Cable acts both as temporary & permanent supports.No requirement of large ground anchorage.Very economical for span between 100 to 500 m.

Offers greater stiffness, torsional & lateral rigidity. It helps bridge to stay more stable against the wind & provide aerodynamic effects.Minimizes deflections.Wide choice of design methods.Outstanding architectural appearance due to its smaller diameter cables.

Simple analysis of harp bridge:given : the weight of the deck is 60 units, so each segment along the deck is 10 units; the angle each cable makes with the deck

can easily calculate the tension in each cable.significance :all cables endure the same high tensionaxial component along the deck is higher (compared to radial)causes bending moments in the tower

Simple analysis of radial bridgegiven : the weight of the deck is 60 units, so each segment along the deck is 10 units; the angle each cable makes with the deck

can easily calculate the tension in each cable.significance :cables further along the deck must endure a higher tension than cables closer to the pieraxial component along the deck is minimal (compared to harp)however, cables congest the very top of the pier

Construction procedure:

Cross-section:

Deck, Tower are made of reinforced concrete.

A box girder supports the deck so as to reduce buckling of the deck from high compressions, twisting or torsion, and distribute among the stays non-uniform loads.

Working:Towers are erected above piers in middle of span.From these piers cables are attached diagonally to the girderBridge has low centre of gravity helps bridge against earthquake. But at the same time, it is weak against wind.Fabrication of the cable bridge is somewhat difficult.

Bridge Failure

Salient features:It is elegant & attractive bridge.It is the most economical between the span 500m 2000m.Bridge gives great architectural view.Considerably saves steel & concrete than other types of bridges.The largest cable stayed bridge is Tatara bridge, Japan having span length=890 m.

LARGEST CABLE STAYED BRIDGETatara Bridge, JapanSpan Length : 890 m

Recent largest application of cable-stay bridge in India is Bandra-Worli sea-link.Bridge length is 4 km having span length 500m on only single pylonIt carries 8 carriage-way

Bandra-Worli sea-link

Gujarat government has given final nod to the cable stayed bridge project in Surat. The one kilometer long two-pillar flood-proof bridge would connect citys Athwa Lines and Pal(Rander-Adajan)SMC Commissioner Aparna told government officials, presently there is no bridge between ONGC-Magdalla bridge and Sardar bridge and there is heavy traffic in the area. Therefore new bridge is needed.Proposed bridge is estimated at cost of Rs86 crore. The project was re-designed as bidders were quoting about 50% higher prices for the project. A new design will not have two approach flyovers.

1)Location:Athwa side: (Agri university on Surat Dumas Road) Adajan side: (Near Dr.V.S.Marg on Surat-Hajira road)2)DetailofCable Stayed portion

a. Length:300 mt.b. Width (Avg.):23.30 mt.c. Area:7050 Sq. Mt.(avg.)d. Pylon

e.tender.cost: :Two nos. each 35 mt. height

143.65 Crore

Construction of Cable Stay Bridge across river Tapi joining Athwa & Adajan

Building A Cable-Stayed BridgeMany things to think about mathematically:Horizontal distance from tower to point of attachmentHeight of point of attachment above bridge levelStretched length of cableAngle between cable and towerExperiments to consider:Cable needs to be tested to see how its stretch varies with the angle to the vertical an experiment to determine how much a length of cable stretches when it supports a mass

Building A Cable-Stayed BridgeThe tower of the bridge forms the vertical side of the right triangle The distance between the points of attachment of preceding cables on the tower should be equalLikewise, the points of attachment of the cables on the beam of the span should be equidistant. You can calculate the length of the remaining cables after the first cable has been installed by applying the proportionality concept or the Pythagorean theorem

Building A Cable-Stayed BridgeWhen building a cable-stayed bridge, to figure out how long the cables need to be, engineers either use scale drawings or Pythagoras and trigonometry to find the required length of cable for each section and the angle between the cable and the vertical

Lets Look at ShapesTriangles are one of the shapes used by the attachment of the cables and the beam this shape is used because of its ability to transfer the tension as the moving load goes across the bridgeIn this bridge, the distance of the cable up the tower is equal to the distance from the tower to connection point on the beam and is a 90 degree angleA rectangle is attached at the convergence point of the beam and tower for stabilityTriangulated bracing between the cables reduces the amplitude of oscillations

Lets Look at Combinations of Side Length1 1/41 1/41 3/41 1/211 The red triangle has two sides of 1 and one side of 1 1/2. If you use what we learned about triangles, a + b > c; 1+1 > 1 1/2.

The yellow triangle has two sides of 1 1/4 and one side of 1 3/4. So, 1 1/4 + 1 1/4 > 1 3/4

Both triangles are very close to an equilateral triangle with all sides being equal. This is the strongest triangle.

Strengths of Cable-Stayed BridgesUses a single support onlyWell-balancedCables can be fabricated separately Horizontal loads are contained within the structureIdeal for use when the river banks are fragile For example if the banks are alluvial mudThe cables disperse a load across more area easilyCables from nodes on tower to road is variant of a triangleGreater inherent rigidity of the triangulated cable-stayed bridges

Math - Helping Me Understand My WorldCivil engineers need to use a combination of geometric shapes to build the strongest structuresExtremely important for engineers to carry out the technical calculations necessary to plan a bridge projectIf the specifications are not correct, the bridge could collapseFor medium length spans between 500 and 2,800 feet, cable-stayed is fast becoming the bridge of choice Modern looking geometric shapes (eye pleasing as well as necessary for strength)Cost effective

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