The Rion-Antirion BridgeConcept, Design and ConstructionJ. Combault 1 and J.P. Teyssandier 21Jacques Combault, Technical Advisor, 27, rue Edgar Degas, 78360 Montesson, France; PH 33 6 12 22 99 68; email: bault@free.fr 2Jean-Paul Teyssandier, Chairman & Managing Director, GEFYRA S.A. (VINCI), 2Rizariou str., 15233 Halandri, Greece; PH +30210 68 58 196; FAX ….…58786; email: teyssandier@AbstractOpened to traffic in August 2004, the Rion-Antirion Bridge crosses the Gulf of Corinth near Patras in western Greece. It consists of an impressive multi cable-stayed span bridge, 2,252 m long connected to the land by two approaches.An exceptional combination of physical conditions made this project quite unusual: high water depth, deep strata of weak soil, strong seismic activity and fault displacements. In addition a risk of heavy ship collision had to be taken into account.The structure has been designed in view of challenging the earthquakes and ensuring the every day serviceability of the link as well. To make the bridge feasible, innovative techniques had to be developed: The strength of the in-situ soil has been improved by means of inclusions; the bridge deck has been suspended on its full length, and therefore isolated as much as it can be.Due to high water depth,construction of the main bridge of the Rion-Antirion Crossing had to face major difficulties. In relation with this, foundation works, including dredging, steel pipe driving, but also precise laying of the required gravel bed under the pylon bases, were forming an impressive work package requiring unusual skills and equipment.To achieve this task, the conceptual design of the entire structure made it possible to simplify, in terms of implementation and reliability, the concept of huge shallow foundations and to prefabricate the major components of a bridge in the most favourable conditions, combining the latest technologies available in the constructionof concrete off-shore oil drilling platforms and large cable stayed bridges.D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .IntroductionLocated between the Peloponese and the continent, at the entry of the Gulf of Corinth in Western Greece, the Rion-Antirion Bridge is intended to replace an existing ferry system.An exceptional combination of environmental and physical conditions made the project quite complex:•large water depth (up to 65 m)•deep soil strata of weak alluviums•strong seismic activity•possible tectonic movements Indeed, the structure spans a stretch of water about 2,500 m long. The seabed presents fairly steep slopes on each side and a long horizontal plateau at a depth of 60 to 70m.No bedrock has been encountered during soil investigations down to a depth of 100m. Based on a geological study, it is believed that the thickness of sediments is greater than 500 m.General trends identified through soils surveys are the following:•a cohesionless layer is present at mudline level consisting of sand and gravel to a thickness of 4 to 7 m, except in one location (near the Antirion side),where its thickness reaches 25m.•underneath this layer, the soil profile, rather erratic and heterogeneous, presents strata of sand, silty sand and silty clay.•below 30 m, the soils are more homogeneous and mainly consist of clays or silty clays.In view of the nature of the soils, liquefaction does not appear to be a problem except on the north shore, where the first 20 m are susceptible of liquefaction.The seismic conditions to be taken into account are presented in the form of a response spectrum at seabed level (see Figure 1). The peak ground acceleration is equal to 0.48 g and the maximum spectral acceleration is equal to 1.2g between 0.2and 1.0 s. This spectrum is supposed to correspond to a 2000 year return period.Figure 1- Design horizontal spectrumD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .It is worth mentioning that the Peloponese drifts away from mainland Greece by a few millimetres per year. For that reason, contractual specifications required the bridge to accommodate possible fault movements up to 2 m in any direction, horizontally and/or vertically, between two adjacent supports.In addition, the bridge supports must be capable to withstand the impact from a 180,000 dwt tanker sailing at 16 knots.Of course, all these difficulties could have been taken into account separately, without major problem, but the conjunction of all these adverse conditions was leading to a formidable challenge. Since a major slope stability problem on the Antirion side eliminated the design of a suspension bridge, from the very beginning of the conceptual design stage, the bridge type and the span lengths had to be selected to simply make the bridge feasible and the global cost of the project acceptable by limiting the number of supports located in the strait and, finally, anexceptional multi-cable-stayed-span bridge was selected.Figure 2– Bridge ElevationDescription of the Main BridgeConnected to the land by two approaches, respectively 392 m long on the Rion side and 239 m long on the Antirion side, this exceptional cable-stayed bridge (see Figure 2) consists of three central spans, 560m long, and two side spans, 286m long.FoundationsThe four pylons of the main bridge simply rest on the seabed through a large concrete substructure foundation, 90m in diameter, 65m high at the deepest location (see Figure 3).To provide sufficient shear strength to the top 20 m of soils, which are rather heterogeneous and of low mechanical characteristics, the upper soil layer of theD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .seabed is reinforced by inclusions to resist large seismic forces unavoidably comingfrom structural inertia forces and hydrodynamic water pressures.Figure 3-Foundation and inclusions: An innovative foundation concept These inclusions are hollow steel pipes, 25 to 30 m long, 2 m in diameter, driven into the upper layer at a regular spacing of 7 to 8 m (depending on the pier).About 150 to 200 pipes weredriven in at each pier location. Theyare topped by a 3 m thick, properlylevelled gravel layer, on which thefoundations rest.Due to the presence ofa thick gravel layer,these inclusionsare not required under one pylon.PylonsThe pylon bases consist of a 1m thick bottom slab and 32 peripheralcells enclosed in a 9m high perimeterwall and covered by a top slab slightlysloping up to a conical shaft. For thedeepest pier, this cone, 38m indiameter at the bottom, 27 m at the top,rises 65m over the gravel bed up to 3 mabove sea level.These huge bases support,through vertical octagonal pylon shafts,24 m wide and nearly 29m high, a15.8m high pyramidal capital whichspreads to form the 40.5 m wide square base of four concrete legs.Figure 4– Global view of aPylonD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Rigidly embedded in the capital to form a monolithic structure,the four legs (4.00 m x 4.00 m),made of high strength concrete, are 78m high; they converge at their tops to impart the rigidity necessary to support asymmetrical service loads and seismic forces.They are topped by a pylon head, 35m high, comprising a steel core embedded in two concrete walls, where stay cables are anchored.From sea bottom to pylon top, the pylons are up to 230 m high (see Figure 4).Deck and CablesThe deck is a composite steel-concrete structure, 27.20m wide, made of a concrete slab,25 to 35 cm thick, connected to twin longitudinal steel I girders, 2.20 m high, braced every 4m by transverse cross beams (see F igure 5 and Figure 6).Figure 5-Typical deck cross sectionIt is fully suspended from 8 sets of 23 pairs of cables and continuous over its total length of 2,252m, with expansion joints at both ends.In the longitudinal direction, the deck is free to accommodate all thermal and tectonic movements and the joints are designed to accommodate 2.5m displacements under service conditions and movements up to 5.0 m under an extreme seismic event.In the transverse direction it is connected to each pylon with 4 hydraulic dampers of 3,500 KN capacity each and an horizontal metallic strut of 10,000 KN capacity (see Figure 6.The stay cables are arranged in two inclined planes according to a semi-fan shape. They are made of 43 to 73 parallel galvanised strands individually protected.Main bridge concept and design philosophyFrom the beginning it has been clear that the critical load for most of the structure was the design seismic loading [3]. The impact from the 180,000 DWT tanker, equivalent to a static horizontal force of 280MN at sea level, generates horizontal forces and overturning moments at the soil-pylon base interface which are smaller than seismic loads generated according to the design spectrum and whichonly necessitates a local strengthening of the pylons in the impact zone.D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .In environmental conditions characterized by poor soil conditions, significant seismic accelerations and unusual water depth,the primary major concerns were the soil bearing capacity and the feasibility of the required foundations. Alternative foundation concepts (such as friction pile foundations, deep embedded caissons and soil substitution) have been investigated with their relative merits in terms of economy, feasibility and technical soundness [2].This analysis showed that a shallow foundation was the most satisfactory solution as long as it was feasible to significantly improve the top 20 m of soils. This has been achieved by means of metallic inclusions, as described here above. Although these foundations looks like piled foundations, they do not at all behave as such: no connection exists between the inclusions and the caisson raft, which will allow for the pylon bases to partially uplift or to slide with respect to the gravel bed; the density of inclusions is much more important and the length smaller than would have been the case if piles had been used.This type of soil reinforcement through metallic inclusions was quite innovative and necessitated extensive numerical studies and centrifuge model tests in the Laboratoire Central des Ponts et Chaussées (France) which validated the concept.The other major points of concern were the large tectonic displacements and the high value of seismic forces to be resisted by the structure. Several possible solutions in terms of structural flexibility were tested but, as long as the pylon bases could move on the gravel bed, it was found that the best way to solve the problem was to make the pylons monolithic and the cable-stayed deck continuous,fully suspended and therefore isolated as much as it could be [1]. Like this, the deck will behave like a pendulum in the transverse direction during a severe seismic event, its lateral movements being buffered and limited by the hydraulic dampers located at each pylon, while it is kept in place during the strongest winds by the horizontal steel strut connected to each pylon which is intended to break only during a seismic eventof low occurrence (over 350 year return period).Figure 6– Fully suspended deck: Concept and connection to the pylonsThese unique features of the project significantly reduce seismic forces in the deck and allow the bridge to accommodate fault movements between adjacent piers thanks to its global structural flexibility.According to capacity design principles, theD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .structure will only be the subject of “controlled damages” under the extreme seismic event at a limited number of well identified locations:•the pylon bases may slightly slide on the gravel bed and partially uplift;•plastic hinges may form in pylons legs;•the wind stabilising struts may fail and thus make the dampers free to operate both in tension and compression and able to dissipate a substantial amount of energy.The dynamic response of the structure was estimated with artificial and natural accelerograms matching the design spectrum. This analysis took into account large displacements, hysteretic behaviour of materials, non linear viscous behaviour of the energy dissipation devices, sliding and uplifting elements at the raft-soil interface and a geological model for the soil-structure interaction [2].In addition to this finite element analysis, a non linear 3D push over analysis was performed for the 4 leg pylons in order to estimate their remaining capacity after the formation of plastic hinges and to confirm their ductile behaviour.Finally, the dynamic relative movement between the deck and a pylon during an extreme seismic event being in the order of 3.50 m, with velocities up to 1.6 m/sec,a prototype test for the dampers was performed in the CALTRANS testing facility at the University of California San Diego and special concrete confinement tests on high strength concrete used for pylon legs,in order to define its strain-stress curves for various confinement ratios, were also performed in San Diego. ConstructionPylon bases were built in two stages near Antirion; the footings were cast first in a 230x 100 m dry dock and the conical shafts were completed in a wet dock.In the dry dock, two cellular pylon footings were cast at a time (see Figure 7). In fact, two different levels in the dock provided 12 m of water for the first footingand 8 m for the other one behind.Figure 7–Pylon bases: Works in the dry dockWhen the first footing, including a 3.2m lift of the conical shaft, was complete, the dock was flooded and the 17 m tall structure was towed out to the wet dock located 1km away (see F igure8).D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Figure 8– From the dry dock to the wet dockAn original idea allowed saving a significant amount of time in the production cycle of the pylon bases.Before the first tow-out, the dry dock was closed by a classical sheet piled dyke which had to be completely removed. Clearly, rebuild and remove again such a dyke would have been time consuming. In fact, the second footing, once moved forward to the deeper part of a the dry dock, was used as a gate after being properly equipped with temporary steel walls (see F igure 9).Figure 9– The dry dock: before and after towing outD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .At the wet dock, where the water depth reaches 50m, the pylon base remained afloat (see Figure 10) and was kept in position by three big chains, two anchored in the sea and one on land. Cells in the base were used to keep the pylon base perfectlyvertical through a differential ballasting system controlled by computer.Figure 10– Pylon base at the wet dock: Progressing towards top of the coneAfter completion of the conical shaft, the pylon base was towed to its final position and immersed on the reinforced soil.Meanwhile, preparation ofthe seabed at the future locationsof pylon bases had beenundertaken (see Figure 11).Dredging the seabed,driving 200 inclusions, placing andlevelling the gravel layer on thetop, with a depth of water reaching65 m, was a major marineoperation which necessitatedspecial equipment and procedures.In fact, a tension-leg barge hasbeen custom-made, based on thewell known concept of tension-legplatforms but used for the firsttime for movable equipment.Figure 11– Driving the inclusions D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S C E . F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .The barge was anchored to deadweights lying on the seabed throughvertical anchor lines (see Figure 12).The tension in these anchor lineswas adjusted in order to give therequired stability to the barge withrespect to sea movements and loadshandled by the crane disposed on itsdeck. By increasing the tension in theanchor lines, the buoyancy of the bargeallowed the dead weights to be liftedfrom the seabed; then the barge,including its weights, could be floatedaway to a new position.Figure 12– The tension leg bargeAfter being immersed at their final position, the pylon bases were filled with water to accelerate settlements, which were significant (between 0.2 and 0.3 m). This pre-loading was maintained during pier shaft and pier head construction, thusallowing a correction for potential differential settlements before erecting pylon legs.Figure 13– Pylon capital and pylon legs under constructionThe huge pyramidal capitals are key elements of the pylon structure, as they withstand tremendous forces coming from the pylon legs. During a major seismic event, three legs can be in tension, while all vertical loads are transferred to the fourth one. For that reason, these capitals are very heavily reinforced (up to 700kg / m3 concrete) and pre-stressed (see Figure 13). Their construction was probably the most strenuous operation of the project.Pylon legs during the construction required a heavy temporary bracing in order to allow them to resist to earthquakes (see Figure 13). This bracing could be removed once legs were connected together at their tops.The steel core of the pylon head was made of two elements which were placed at their final location by a huge floating crane able to reach a height of 170mabove sea level (see Figure 14).D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .Figure 14– Placing the steel core of the pylon headThe method of construction of the composite steel – concrete deck was similar to the one successfully used on the second Severn crossing: deck segments, 12m long, were prefabricated on the yard, including their concrete slab.They were placed at their final location by the floating crane (see Figure 15) and bolted to the previously assembled segments, using the classical balanced cantilever erection method. Only small joints providing enough space for anappropriate steel reinforcement overlapping had to be cast in place.Figure 15– Placing 12 m long segmentsD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .The deck was erected from two pylons at the same time. Five to seven decksegments were put in place each week. In total the deck erection took 13 months.ConclusionThe Rion – Antirion Bridge had to overcome an exceptional combination of adverse environmental conditions: water depth up to 65m, deep soil strata of weak alluviums, strong seismic activity and tectonic movements.This resulted in a unique multi-span cable-stayed bridge consisting of a continuous deck, 2252 metres long and fully suspended from four pylons.The pylons rest directly on the sea bed, through a gravel layer allowing them to be the subject of controlled displacements under the most severe earthquake. Based on an innovative concept,the top 20m of soils located under the large diameter bases (90 m) of three of the pylons are reinforced by means of metallic inclusions.The design and construction of this $ 800 million project have been undertaken under a private BOT scheme, led by the French company VINCI.Completed in August 2004, the Rion-Antirion Bridge has been opened to traffic 4 months before the contractual deadline.References[1]Combault, J. - Morand, P. - Pecker, A. (2000). Structural Response of the Rion-Antirion Bridge. 12th World Conference on earthquake Engineering. Auckland, New Zealand.[2]Pecker, A.(2003). Aseismic foundation design process, Lessons learned from two major projects: The Vasco da Gama and the Rion-Antirion Bridges. ACI International Conference on Seismic Bridge Design and Retrofit . La Jolla, California.[3]Teyssandier, J.P. -Combault, J. - Morand, P. (2000). The Rion-Antirion Bridge Design and Construction.12th World Conference on earthquake Engineering.Auckland, New Zealand.D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y T o n g j i U n i v e r s i t y o n 07/10/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .。
