Cable-Stayed Bridges

-JIGAR .S.SHAH(CP1712)-ADNAN SHAIKH(CP1812)-MEGHA SINGH(CP1912)

DIFFERENCE BETWEEN CABLE STAYED BRIDGE AND CABLE SUSPENSION BRIDGE A multiple-tower cable-stayed bridge may appear similar to a 

suspension bridge, but in fact is very different in principle and in the method of construction.

In the suspension bridge, a large cable hangs between two towers, and is fastened at each end to anchorages in the ground or to a massive structure.

These cables form the primary load-bearing structure for the bridge deck. Before the deck is installed, the cables are under tension from only their own weight.

Smaller cables or rods are then suspended from the main cable, and used to support the load of the bridge deck, which is lifted in sections and attached to the suspender cables.

The tension on the cables must be transferred to the earth by the anchorages, which are sometimes difficult to construct owing to poor soil conditions.

much greater stiffness than the suspension bridge, so that deformations of the deck under live loads are reduced

can be constructed by cantilevering out from the tower - the cables act both as temporary and permanent supports to the bridge deck

for a symmetrical bridge (i.e. spans on either side of the tower are the same), the horizontal forces balance and large ground anchorages are not required.

ADVANTAGES OF CABLE STAYED BRIDGES

INTRODUCTION A cable-stayed bridge, one of the most modern bridges,

consists of a continuous strong beam (girder) with one or more pillars or towers in the middle

Cables stretch diagonally between these pillars or towers and the beam .These cables support the beam

The cables are anchored in the tower rather than at the end

LOAD TRANSMISSIONslab

Cables

pylons

Pile cap

piles

soil5

Tension

Compression

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COMPONENTS OF CABLE STAYED BRIDGE

CLASSIFICATIONS

Based on arrangements of the cables• Radiating• Harp• Fan• star

Based on the shape of pylon• A-type• H-type• Y-type

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CLASSIFICATIONSradial : cables connect evenly throughout the deck, but all converge on the top of the pier

harp : cables are parallel, and evenly spaced along the deck and the pier

fan : a combination of radial and harp types

star-shaped : cables are connected to two opposite points on the pier

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SHAPES OF PYLON

CABLE A cable may be composed of one or more structural ropes,

structural strands, locked coil strands or parallel wire strands. A strand is an assembly of wires formed helically around centre

wire in one or more symmetrical layers. A strand can be used either as an individual load-carrying member,

where radius or curvature is not a major requirement, or as a component in the manufacture of the structural rope.

A rope is composed of a plurality of strands helically laid around a core. In contrast to the strand, a rope provides increased curvature capability and is used where curvature of the cable becomes an important consideration.

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TYPES OF CABLE

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Cables are made of high-strength steel, usually encased in a plastic or steel covering that is filled with grout , a fine grained form of concrete, for protection against corrosion.

SELECTION OF CABLE CONFIGURATION The selection of cable configuration and number of

cables is dependent mainly on length of the span, type of loadings, number of roadway lanes, height of towers, and the designer’s individual sense of proportion and aesthetics.

Cost also plays important role in deciding the selection. Using less number of cables increases concentrated load

at a single point thereby requiring additional reinforcement for the deck slab as well as pylon .

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POSITIONS OF THE CABLES IN SPACE Two plane system

Two Vertical Planes System Two Inclined Planes System

The Single Plane System

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Two Vertical Planes System

In this type of system there are two parallel sets of cables and the tower on the either sides of the bridge, which lie in the same vertical plane.

1. The cable anchorages may be situated outside the deck structure, which is better than the other in terms of space as no deck area of the deck surface is obstructed by the presence of the cables and the towers.

2. but this requires substantial cantilevers to be constructed in order to transfer the shear and the bending moment into the deck structure.

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When the cables and tower lie within the cross-section of the bridge, the area taken up cannot be utilized as a part of the roadway and may be only partly used for the sidewalk. Thus as area of the deck surface is made non-effective and has to be compensated for by increasing overall width of the deck.

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TWO INCLINED PLANES SYSTEM In this system the cables run from the edges of the bridge deck to a

point above the centreline of the bridge on an A-shaped tower or λ-shaped or diamond shaped pylon.

This arrangement can be recommended for very long spans where the tower has to be very high and needs the lateral stiffness given by the triangle and the frame junction.

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THE SINGLE PLANE SYSTEM This type of system consists of bridges with only one vertical

plane of stay cables along the middle longitudinal axis of the superstructure

As the cables are located in a single centre vertical strip thus all the space is utilized by the traffic.

This system also creates a lane separation as a natural continuation of the highway approaches to the bridge.

longitudinal arrangements of the cables used with two planes bridges are also applied to single centre girder bridges.

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CASE STUDY:BANDRA WORLI SEA LINK

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BRIDGE DETAILS: LENGTH OF SEA LINK: 5600 m LENGTH OF CABLE STAY PORTION: 600 m HEIGHT OF PYLON/TOWER : 123 m NO. OF PIERS : 620 LONGEST SPAN : 2x250 m LOCATION : A CLOVERLEAF INTERCHANGE AT MAHIM

INTERSECTION AND A FLYOVER AT THE LOVEGROVE INTERSECTION HAVE BEEN PROPOSED AS PART OF THIS PROJECT TO ENHANCE THE FASTER AND SAFE TRAFFIC DISPERSAL.

CLIENT : MSRDC MAIN CONTRACTOR : HCC TOTAL PROJECT COST : Rs 850 CRORE SCHEDULED INITIALIZATION & COMPLETION: MAY, 1999 &

MAY, 2002 ACTUAL COMPLETION : AUGUST, 2009 AMOUNT OF CONC. USED : 0.2 million cum.

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SUB SURFACE EXPLORATION

INITIAL GEOTECHNICAL INVESTIGATION

25 BORE HOLES ALONG THE LENGTH TO OBTAIN THE SOIL PROFILE.

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SUB STRUCTURE CONSTRUCTION

PILING: TYPE OF PILES : COMBINED END EARING AND

FRICTION PILES DIA OF PILES USED : 1.5 – 2 m DEPTH OF PILES : 5.15 – 663.4 m PILE GROUP UNDER THE PYLON : 40 NOS. CONST. TYPE : BORED CAST IN SITU TECHNOLOGY USED : REVERSE CIRCULATION DRILL SUPPORT STRUCTURES : COFFERDAM & SHEET

PILING PILE CAP THK – 3.5 m CONCRETE USED – M60, HPC PIER LENGTH – 4-6 m DEPENDING UPON THE GRADIENT

OF BED

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COFFER DAM CONSTRUCTION

A TEMPORARY WATER TIGHT STRUCTURE TO FACILITATE CONST. OF PROJECT WHICH ARE SUBMERGED IN WATER.

IT CONSIST OF CASINGS OF 1.5 m DIA AND SHEET PILES

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PILING ONCE THE COFFER DAM IS CONSTRUCTED, WATER IS PUMPED OUT . DEWATERING TECHNIQUE ADOPTED WAS WELL POINT SYSTEM. PILING TECHNIQUE USED WAS REVERSE

CIRCULATION DRILL. IN THIS METHOD, PRECAST

SEGMENT IS PLACED ON SOIL & DRILLING IS DONE WITH DRILL BIT

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RCD DRILL BIT

DRILL BIT CONSISTS OF PNEUMATIC PISTON

DEPTH ACHIEVABLE : 500 m

BIT DIA : 13 – 20 cm MATERIAL : TUNGSTEN

STEEL OUTPUT : 900 – 1150 cfm @

350 RPM

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PYLON CONSTRUCTION

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LOWER PLYON CONSTRUCTION

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LOWER PYLON CONSISTS OF :1. PIER TABLE2. LOWER PIER LEGS

CONST. METHOD USED : SELF CLIMBING FORM

CONST.

CONST. IS DONE IN LIFTS. 6 LIFTS REQUIRED FOR CONST OF LOWER PYLON.

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UPPER PYLON

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WHILE CONSTRUCTINGTHE UPPER TOWER LEG, THE CARE WAS TO BE TAKEN THAT THE REINFOCEMENT DOESNOT FALL DUE TO ITS SELF WEIGHT, THAT IS WHY EMBEDDED TUBES WERE FIT IN JUMP FORM TO PROVIDE EXTRA SUPPORT IN LEGS.

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CABLE STAYED BRIDGE

SUPERSTRUCTURE CONSTRUCTION

SUPERSTRUCTURE CONSTRUCTION

Precast Segmental Construction involving Match Casting Span by Span Erection for approach spans

Parameters for segment casting Alignment of the individual span to which segment

belong. Precamber necessary to take care of deformations of

the girder due to self weight, prestress and other permanent loads.

Necessary corrections for errors in the casting of adjacent segment cast earlier, while match casting. 42

CASTING YARD

43PLAN of Casting Yard

CASTING YARD Total number of segments – 2500 & more. Three types of segment

Approach Span Segment Main Cable stayed segment Segment on Piers

Size of Approach Segment –18.1m x 3.2m x 3.0m Size of Main Cable Stay Segment – 20.8m x 3.2m x 3m Weight of each Segment – 150 tonnes Total length of Casting Yard- 350m Capacity – 300 segments at a time

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Segments placed in Casting Yard

ERECTION OF SEGMENTS

The Erection Gantry does the erection of span.

A typical 50m span comprises of 15 numbers of precast segments

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The segments are transported to the site with the help of barges.

Each segment is lifted and all the segments in a single span are aligned together and brought about at the same level.

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At the time of match casting High Tensile Steel Rods are passed through the ducts provided in the segments and tightened with the help of a Winch machine.

Neutobond BC solution is used so that the two segments can be aligned together.

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Asian Hercules used to displace Erection Gantry

ERECTION OF STAY CABLES

The cable - stayed portion is 600 meters in overall length. It consists of two 250 meters cable supported main spans flanked by 50

meters conventional approach spans. A centre tower with an overall height of 128 meters above pile cap

level supports the superstructure by means of four planes of stay cables in a semi - fan arrangement.

Cable spacing is 6.0 meters along the bridge deck and are tied up to every alternate girder.

Big tower -264 stay cables Length- Min- 85m Max- 250m Small tower -160 stay cables Length- Min- 30m Max- 80m

In each there are approx. 135 strands stressed with the help

of a hydraulic jack.

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DESCRIPTION OF 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 bridge

In 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 angle

A rectangle is attached at the convergence point of the beam and tower for stability

Triangulated bracing between the cables reduces the amplitude of oscillations

 CONTINUITY PT AND GROUTING Once the Deck is complete Post Tensioning of all the

segments is done so as to bring them to a specific predetermined geometry. 

The grouting of the bridge includes a major task of fill up the space left in the holes for the PT cables.

CABLE FORCE ADJUSTMENT AND FINE TUNING Iterative process Last stage  Rechecking of tension forces in each cable so as to

confirm that it equals the forces. 1 to 2% of variation.

BENEFITS OF BANDRA-WORLI SEA LINK

1) It is estimated that the sea link will help saving Rs. 10 million annually due to congestion in traffic and length of the previous route and shorter new route.

2) While earlier it used to take 40 minutes for drive between Bandra and Worli, now the distance can be covered in mere 8 minutes resulting in large savings in time.

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