signature cable stayed bridge

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The Signature Cable-Stayed Bridge in New Delhi

Mike SchlaichProf. Dr.sc.techn.Technische Universitt

Berlin, Germanywww.massivbau.tu-berlin.de

and schlaich bergermannund partnerwww.sbp.de

Mike Schlaich, born 1960 inCleveland-Ohio, received his civilengineering and Dr. degree fromthe ETH Zrich. He is managingdirector of schlaich bergermannund partner and Professor at the"Technische Universitt" Berlin.

Uwe BurkhardtProject Managerschlaich bergermann und

partnerBerlin, [email protected]

Uwe Burkhardt received hisstructural engineering degreefrom the University of Stuttgart,Germany. Since 2001 he worksfor schlaich bergermann und

partner. He is project manager ofthe Signature Bridge in NewDelhi at schlaich bergermann und

partner.

Summary

The Yamuna crossing in New Delhi, a single-pylon cable-stayed bridge with a main span of about250m length will be Indias longest-span bridge of this kind. The bridge is presently underconstruction and will be opened to traffic in 2014. In the paper the authors will elaborate on designand analysis of the superstructure of the bridge, and will put it in the context of other such long-span bridges in India and worldwide.

Keywords:cable-stayed bridges, conceptual design, signature bridges, context, bridge construction,India.

1. Introduction

Whenever designing engineering structures we seek to minimise material quantities by a logicaldesign and reduce the cost by indigenous construction. These ideals have been challenged duringthe recent years when more and more clients explicitly asked for "iconic" structures and"landmarks". The "Bilbao effect" is a wide spread expression and especially in Great Britain manyMillennium Projects were promoted, also in the field of bridges. Since then "Signature" bridgeshave become a frequent request. This development also affects the design of cable-stayed bridgessince naturally they are perhaps the most economic and elegant way to bridge long spans.

In general it is a positive development that the request for signature bridges in specific locations isgrowing. It shows that bridges are now in the public awareness as structures which influence, shapeor even improve our built environment. Bridges are acknowledged as a part of building cultureturning infrastructure into civilisation. We, the engineers, should use this trend and prove that good

design can generally achieved with little extra cost. In the following sections the potential ofindigenous construction and signature properties of cable-stayed bridges is demonstrated at severalexamples which have been built in India and Hong Kong and more detailed at the example of theSignature Bridge in Delhi which is currently under construction.

2. Cable stayed bridges

2.1 Conceptual design and context

It is the existing boundary conditions that directly influence all infrastructure projects includingbridges. These conditions lead to unique designs, to bridges that fit only at their genuine location atone time. Such boundary conditions may be simultaneously topographical, financial, historical orsocial. It may be the landscape that surrounds the future bridge or the "chemistry" of the design

team. The design of a bridge is often a compromise of conflicting boundary conditions. Howeverthe more complex and the more contradicting the conditions are, the greater is the chance to achieve


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an innovative or even surprising design.

The main advantage of cable-stayed bridges is their favourable load bearing behaviour - the cables,mast and the deck form a large truss and consequently carry loads mainly by compression andtension. The typical cable-stayed bridge consists of three spans, one main span with a length L andtwo lateral spans with about 0.4L. The most visible design parameter is the way the cables are

placed along the deck. The cable can be centred or lateral in cross direction and fan, harp or semi-harp shaped in elevation. Other important design features are the shape of the pylons or masts andthe deck type [1].

Cable stayed bridges are usually the most economic choice for spans from 100 to 200m up to1000m. When compared to suspension bridges, cable-stayed bridges offer the advantages that theyare self-anchored even during construction and, therefore, do not required costly counterweights assuspension bridges and that they react with only small deformations to live loads.

With increasing span, however, the axial forces in the deck increase. Therefore, in general,composite decks are a very advantageous solution. Depending on the situation, the welded, boltedor even riveted steel grids can be brought to the site in segments on barges or trucks and beassembled from cranes from the bridge deck in the free cantilevering method. The concrete deckcan be assembled using prefabricated slab elements and then only the joints must be concreted in-

situ. In regards to corrosion, the steel girders are easy to inspect and maintain. Because the girdersare open and aerated they tend not to rust and there is no interior corrosion.

Cable stayed as well as many other cable-supported bridges please because of their light-weightappearance and often impress simply because of their sheer size: the potential of naturally achievinga signature structure is high. The misunderstanding however, is that icons, landmarks and signature

bridges cannot be ordered. Great inventions on command are hardly possible. The high expectationsthus placed on the designer may lead to over-reactions. Engineering values such as economy androbustness are thrown over board for the sake of not-yet-seen pompus structures. Still, we shoulduse this trend to show that bridges as all engineering structures play an important role in the

building culture, to prove that good design can generally be achieved with little extra cost and thatderiving the concept from the given boundary conditions is perhaps the most promising designapproach. The following examples show the ample range of choices that exists only in the field ofcable stayed bridge design. More examples can be found in [2].

2.2 Bridge Examples

For the Second Hooghly Bridge, today Vidyasagar Setu, in Kolkata with a main span of 457m theclient requested the bridge to be built with local labour, local skills and materials, i.e. indigenousconstruction [3]. Since weldable steel and HSFG bolts were not available at that time, only a rivetedstructure was possible and an orthotropic steel deck, the international standard at that time, was not

possible. Thus, Vidyasagar Setu was not only record span at the time, it also became the first cable-stayed bridge with a composite deck. A steel grid acting compositely with a concrete deck slab ontop. Another special feature of this bridge is the parallel wire cables made in India, that connect to

passive anchorages at the deck and that can be retensioned in the pylon head.

Fig. 1: Second Hooghly Bridge (Vidyasagar Setu), Kolkata, India ( Roland Halbe)


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The Ting Kau Bridge in Hong Kong is one of the few multispan cable-stayed bridges built so far [4].An under-water hill offered the opportunity to built a central mast which led to economical deckspan dimensions and a total cable supported deck length of 1177m. The design was furthergoverned by the typhoon wind loads in Hong Kong. Aerodynamic stability of the deck for windspeeds up to 95m/s had to be achieved. A slender deck of only 1,75m height supported by four cable

planes reflects this. The high wind loads also led to slender masts shaped for minimum wind

resistance that are stabilised in the transverse direction by cables just like the masts of a sail boat.

The designers of the Second Vivekananda Bridge in Kolkata, IBT from San Diego, USA togetherwith CES and Parsons, have consciously adjusted this extradosed bridge to the spans anddimensions of the adjacent first Vivekananda Bridge. This first bridge was built in the first half ofthe 20th century and consists of seven arch-shaped steel trusses of 110m span each. The seven spansof the new bridge are, therefore, of equal size. The material is different, parallel strand cablessupport concrete box girders made of match-cast segments. The extradosed bridge type is widelyused in Japan and is characterised by very shallow cables. This leads to masts of reduced height,which in this case allows for an overall bridge height that does not obstruct the view to theDakshineshwar temple which is also in its vicinity.

Fig. 2: Ting Kau Bridge, Hong Kong ( Roland Halbe)

Fig. 3: Second Vivekananda Bridge (Nivedita Bridge), Kolkata, India ( Alan Cook)

(Independent Consultants: schlaich bergermann und partner)


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3. Signature Bridge Delhi

3.1 Conceptual design

The following paragraphs about the Signature Bridge Delhi or Yamuna Bridge at Wazirabad are ashortened version of [5]. For the Yamuna Bridge at Wazirabad in New Delhi, the client, Delhi

Tourism and Transport Corporation (DTTDC), explicitly opted for a signature bridge. The solutionis a bridge with a dynamically shaped pylon that symbolises modern India, and that makesstructural sense at the same time. The weight of the backwardly inclined pylon compensates part ofthe dead weight of the deck, thus reducing the number of backstay cables. The pylon body is shapedso that the forces of the cables entering in two planes from the front and leaving in one backstay

plane are transferred in a direct way. The top of the pylon is formed by a steel-glass structure thathouses inspection platforms, which can also be used as viewing platforms and be illuminated atnight, thus converting the pylon head into a beacon seen from afar.

The Yamuna Bridge at Wazirabad is an asymmetric cable-stayed bridge with a main span of 251mand total length of 675m. Its composite deck carries 8 lanes (4 in each direction). It isapproximately 35m wide and is supported by lateral cables spaced at 13,5m intervals. Towards theapproaches the same deck section continues with piers supporting it at 36 m intervals. The height of

the steel tower is approximately 150m.

The Signature Bridge Delhi is one of the many infrastructure projects that are presently being builtin New Delhi. It is needed to ease the burden of heavy traffic that today crosses the Yamuna river inthe north of New Delhi on a two lane road over the Wazirabad barrage. The area around the bridge

will later be developed into a tourism destination and the Yamuna river will be widened at thislocation to lake-like dimensions. Therefore, the client requested a rather long-span, but light-weight

bridge and a signature design that could become one of the areas theme attractions and a landmarkfor New Delhi. The bridge also will have a state-of-the-art lighting system, an elaborated bridgehealth monitoring system, internal elevators and an external mechanised cleaning system.

Based on this context, during various design sessions with a strongly involved client, numerousalternatives for the future bridge were drafted and evaluated. The outcome is a cable-stayed bridgethat has some novel features giving it an easily identifiable signature appearance. At the same timethe design evolves from well proven structural solutions such as a slender composite deck, verysimilar to the ones of Second Hooghly Bridge and Ting Kau Bridge described in section 2.2.

The pylon with its large glass top leaves ample room for symbolic interpretation. The layout of the

upper part of the pylon allows for large-scale artistic paintings, which is not possible with pylons ofconventional cable-stayed bridges. Applying typical Indian ornamental graphics to the pylon topwill further enhance its uniqueness.

Fig. 4: Elevation of Signature Bridge Delhi (Yamuna Bridge at Wazirabad)


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Due to its inclination, the pylon weight can compensate a significant part of the dead load of themain span. While other bridges of similar appearance like the Alamillo Bridge in Seville and theErasmus Bridge in Rotterdam feature inclined masts which widen towards the deck, here the mast

becomes more slender to the bottom since there is a hinge between pylon base and pylon pier,which is in tune with the overall truss-like behaviour of cable-stayed bridges. Since the resultingforce of the backstays reaches the pylon at a higher level than the one from the main span cables, amoment is induced which counteracts that which is caused by the bend, i.e. the change of directionof the pylon legs.

The result of the conceptual design process for the Yamuna bridge is a structure that tries tocombine robustness and structural sanity with the expectations that come with a signature bridge.Only after the concept was approved by the Delhi Government and the Delhi Urban ArtsCommission, was the detailed design of the Yamuna Bridge developed.

3.2 Superstructure Design and Analysis

Two four lane carriageways, typically 14m wide and separated by a concrete crash barrier as well astwo lateral emergency pathways, form the deck of the bridge that totals 35,2m in width. The deck isformed of outer I-shaped longitudinal main girders and I-shaped cross girders at 4,5m intervals. A

third central main girder is placed to distribute heavy live loads onto several cross girders. Allstructural steel is grade S355 (or the Indian equivalent). Shop welding and site splices with highstrength friction grip bolts will be used. The pre-cast deck slabs of concrete grade M50 span 4,5m

between cross girders. Their standard thickness of 250mm increases to 700mm at the main towerand in the area of the backstay anchorage. Such a composite deck not only permits quick and simpleerection of the steel grid, but also offers the economical advantage of having the concrete balancingthe horizontal cable thrust, a cost-free prestress.

The deck is transversally restrained on both ends of the bridge and at the pylon. The onlylongitudinal deck restraint is at the pylon. The expected longitudinal movement of the deck at itswestern end is +/-250mm approximately.

The deck is supported by two cable planes. The cables are directly anchored to the webs of the

outer main girders at 13,5m distances with their dead end, and are stressed from within the stressingchambers at the top of the pylon. The cables will be made of bundles of parallel 0,6 strands ofgrade 1770. Depending on the location, the number of strands per cable varies from 55 to 123 nos.

Fig. 5: Virtual image of Ornamental Painting on the Pylon


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at the main span and 127 Nos. for each of the backstays. Corrosion protection will be applied tointernational practice, i.e. with hot dip galvanised wires and individually coated strands that arecovered by an outer PE-pipe. In the backstay area, the lower part of the cables will be fire protected.

The pylon consists of two legs made of steel boxes which merge into one upper pylon zone wherethe cables supporting the main span and the backstays are anchored and interconnected.

Furthermore, the upper tower is designed as a hollow box section made of a load bearing skinstiffened by internal stiffeners and bracings. The pylon is monolithically connected to the deck. Itintroduces horizontal forces in the longitudinal direction into the concrete of the deck. Thehorizontal forces in the transverse direction are carried by a strong steel cross tie that connects thetwo legs at the level of the cross girders. Below the deck the pylon legs are supported on largespherical bearings in order not to induce bending into the substructure. Each bearing must transmitvertical forces up to 170 MN. The bearings rest on concrete piers with a raft foundation. Moreinformation on the substructure can be found in a separate contribution of these proceedings byH. Subba Rao.

The major part of the steel for the pylon is of grade S355; only in very highly stressed zones, suchas the area where the pylon is bent, grade S460 steel is used. Above the top-most cable anchoragethe pylon rises farther some 30m forming the pylon head, a glass-covered steel structure that housesthe illumination system and the platforms mentioned earlier.

The structure has been designed according to Indian codes of practice, i.e. using allowable stressdesign and loads according to IRC:6-2000. For issues where Indian codes are not available or notapplicable, the Eurocodes were used, while for the design of the cables, the Setra guidelines oncable stays were consulted.

For the global analysis, a 3D finite-element-model of the bridge was used. The deck was modelledusing shell elements for the concrete slab rigidly connected to beam elements that represent thesteelwork below. The deck is designed to withstand the failure of any one cable and it is this loadcase that often governed the design. The pylon was also modelled with 3D shell elements. Secondorder effects were considered by geometrically non-linear algorithms applied to the pre-deformedsystem.

Extensive seismic analysis was done by IIT Roorkee based on site specific parameters using threemethods: (i) equivalent static method, (ii) response spectrum method, (iii) linear time historyanalysis method. The results of the studies show that seismic forces from the equivalent staticmethod with a uniform lateral load of 10 % of gravity are on the safe side.

In the wind tunnel, section model tests proved that flutter will not occur. Of importance was themodelling of the pylon in the wind tunnel in order to obtain realistic assumptions for the wind loadsto be applied.

Fig. 6: Substructure work on eastern and western shore ( Gammon India Ltd.)


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3.3 Fabrication and construction

Since the Yamuna River is presently not yet dammed to form the lake and since the deck is onlyabout 12 m above the ground, the usual free-cantilevering erection of the deck of cable-stayed

bridges is not necessary. Rather, the deck will be built on temporary supports. Those, however, mustbe able to resist high waters should deck erection continue during the rainy season.

The steelwork was designed in such a manner that large, but still transportable sections, can beprefabricated in the protected environment of a workshop. The individual sections will then bebolted on site, a quick and safe construction method. To minimize the amount of bolts and the extraweight of splice plates most of the compression forces are transmitted via butt contact. Therefore,all main girder splices and the horizontal pylon splice surfaces have to be machined to ensure a

proper fit and butt contact. It is essential to test this fit in a trial assembly in the workshop andconfirm it by intensive survey before the sections are shipped to site.

Most of the over 14.000to of structural steelwork havebeen fabricated in a workshop in China and are currentlytransported to Delhi. The steelwork erection on site isexpected to start in July or August 2013, as soon as themonsoon allows. During the construction the inclined

pylon will rest on a temporary steel seat until sufficientcables have been installed to balance its weight.

Parallel to the steelwork erection the precast concretepanels will be put in place and the joints will be grouted.Currently production of precast panels is in full swing.

Only after the last cable is installed the temporary

supports in the river bed will be removed and the bridgefurniture and the glass pylon head will be installed.

Fig. 7:Machining of contact surfaces (left) and trial assembly of the deck (right)

Fig. 8:Fabrication of precast concrete panels

( Gammon India Ltd.)


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4. Summary

Only thanks to the persistence of the client DTTDC the Signature Bridge Delhi is finally becominga success. The design was finished 2007 but then the project had to face the tremendous increase insteel prizes in 2007, when suddenly many signature projects, like the Olympic stadium in Beijing,absorbed the whole steel production worldwide. Thereafter it survived the global financial crisis

and land acquisition problems. Now the bridge project is consistently moving forward to itscompletion in 2014.

The Signature Bridge will be a symbol of emerging India. It is a big leap forward compared to thestill riveted Second Hooghly Bridge 30 years ago. Simultaneously it will be a symbol ofglobalization. Not only the design team, consisting of the Indian engineers of CCPL and the Indianarchitect Ratan J. Batliboi who worked jointly with schlaich bergermann und partner Germany, butalso the checking engineers are formed of an Indian-French joint venture and finally the contractoris a Indian-Brazilian-Italian consortium with a Chinese steel subcontractor. Taking globalizationinto account this project is an example of modern indigenous design and construction.

5. References

[1]

WALTER R., at. al., "Cable Stayed Bridges", Thomas Telford Publishing, London, 2003.

[2] SCHLAICH M., "Indigenous and Signature Cable Stayed Bridges - Attitudes TowardsImprovement of Infrastructure", CENeM, Kolkata, 2007.

[3] SCHLAICH J., BERGERMANN R., "Cable-Stayed Bridges with Composite StiffeningGirders - The Second Hooghly Bridge in Calcutta",Proceedings of the Sino-AmericanSymposium on Bridge and Structural Engineering, Peking, 1982.

[4] BERGERMANN R., SCHLAICH M., "The Ting Kau Bridge in Hong Kong",ProceedingsIABSE Symposium Kobe, Japan, 1998.

[5] SCHLAICH M., SUBBARAO H., KURIAN J., "A Signature Cable-Stayed Bridge in India -The Yamuna Bridge at Wazirabad in New Delhi", SEI Journal, 1/2013.

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