Rion-Antirion Bridge

Name in local language:	Γέφυρα Ρίου-Αντίρριου "Χαρίλαος Τρικούπης"
Other name(s):	Rion-Antirion Bridge
Beginning of works:	1999
Completion:	7 August 2004
Status:	in use

Location:	Rion, Achaea, West Greece, Greece Antirion, Aitolia-Acarnania, West Greece, Greece
Coordinates:	38° 19' 1" N    21° 46' 31" E

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1880	Harilaos Trikoupis, then prime minister of Greece, is among the first to imagine a link at this location.
21 May 2004	The last piece of the deck is mounted.
Night of 7 August 2004 — 8 August 2004	In a grand ceremony including major fireworks, the bridge is officially inaugurated.
8 August 2004	Irina Szewinska from Poland and winner at the olympic games in Montreal and Mexico, Otto Rehagel, coach of the Greek soccer team that won the Euro 2004 championship, and Stratos Apostolakis, coach of the Greek Olympic soccer team, carry the Olympic flame across the bridge on its way to Athens for the Summer Olympics.
12 August 2004	The bridge is opened to traffic.
2005	Outstanding Civil Engineering Achievement (ASCE)
28 January 2005	One of the cables catches fire, possibly after being hit by lightning. The bridge is closed to traffic indefinitely in order to assess the damage.
1 February 2005	The bridge is re-opened to traffic, though use is limited to a single lane until the damage to the cable-stay has been repaired.
2006	Outstanding Structure Award (IABSE)
2006	Outstanding Concrete Structure Award (FIB)

Concessionaire Gefyra and contractor Kinopraxia are composed of:

• Vinci (53%)
• J&P Hellas (11,2%)
• TEV (7,74%)
• Helleniki Technodomiki (7,74%)
• Athena (7,74%)
• Proodeftiki (7,74%)
• Sarandopoulos (7,74%)

Financing:

• Greek Government: 43%
• European Investment Bank: 47%
• Stock holder capital: 10%

Expected traffic: 11 000 vehicles/day

Duration of construction: 5 years
Length of the concession: 42 years

The bridge is designed to withstand earthquakes of 7.5 on the Richter scale.

General

The Rion-Antirion Bridge crosses the Gulf of Korinth at its narrowest westerly location.

The design had to overcome some unusual problems. The difficult geology requires a minimum of piers. In the bridge region the sea is an average of 60 m deep, at places more than 65 m. The ground consists of a 20 – 30 m thick layer of clay, covered by a layer of sand and gravel of varying thickness. Rock is estimated only at about 800 m depth.

The whole region is subject to earthquakes with an intensity of 6.5 on the Richter scale. The maximum ground acceleration can reach 0.48 g, the corresponding maximum response acceleration in the bridge is 1.2 g in the eigenfrequency range of 1 – 5 Hz. In addition, horizontal and vertical tectonic dislocations of up to 2 m have to be considered. Although commercial ship traffic has a low density, the piers have to resist an impact of a 180 000 t oil tanker with a speed of 16 knots.

The main bridge has a length of 2 252 m with 2 880 m approaches on each side. The Rion-Antirion Bridge was designed by Jacques Combault. Michel Virlogeux was an important advisor.

Design

Based on the above conditions several alternate designs were considered in order to find the most economic solution. This led to a five-span cable-stayed bridge with three inner spans of 560 m and two side spans of 286 m.

A series of cable-stayed bridges of this size means a record for this type of bridge. The tower heads are stabilized by the four stiff tower legs with A-shapes in both directions. The beam is supported by 8 × 23 pairs of stay cables uniformly distributed over the length of the bridge. Vertically the beam is only supported on the two outer common piers with the approaches.

A detailed analysis of the interaction between foundations and superstructure showed that the beam, continuous over its full length and fully supported by stay cables, is able to adjust without permanent damage to the large possible horizontal and vertical tectonic dislocations of the towers.

Beam

The 27.2 m wide composite bridge beam comprises two open steel main girders with a depths of 2.2 m (h : l = 2.2 : 560 =1 : 252), steel cross girders at a distance of 4 m, and a 24 cm thick concrete slab. All changes in lengths, due to temperature and tectonic dislocations, are only taken up at the ends by roadway joints with ± 2 m dilatation. In the transverse direction the beam is connected to each tower with four dampers.

Foundations

The hollow reinforced concrete foundations with 89.5 m diameter are 9 m high at the outside and 13.5 m at the connection to the cone- shaped tower piers. At the inside they are stiffened by a torsion ring and radial beams. The foundations of the first three towers on the Rion side, which have a depths of 35 m, are directly resting on a gravel base layer which is strengthened by steel piles. These piles are 25 – 30 m long and placed on a 7 m by 7 m grid on a circular area of 130 m diameter. The base layer on top of the steel piles consists of a precisely leveled layer of gravel. The steel pipes are not directly load-bearing. They assist in distributing the tower loads into the ground and in limiting differential settlements. The gravel layer has to transfer the horizontal loads from the bridge onto the steel piles and surrounding ground plastically, thereby avoiding a failure plane in the clay layer.

Towers

The concrete towers comprise a three-part pier with the tower legs above. A cone-shaped lower part with a diameter of 37.99 m at the base and 26.93 m at the top is fixed to the foundation. On it rests an octagonal shaft, 28.4 m high, with a pyramid-shaped 19.3 m high part on top. The tower legs have cross-sections of 4 m × 4 m. The tower head for the cable anchorage is composite with a steel box cast into concrete.

Stay cables

For the Rion-Antirion Bridge parallel strand cables were, as usual today, selected. At the beam they are anchored above the roadway at a web extension. At the tower heads theyconverge into composite anchorages.

Earthquake

The conditions for earthquake are based on a response spectrum on the ground with a 2000-year return period. The highest ground acceleration comes to 1.2 g over a range of eigenfrequencies between 1 and 5 Hz. There is no connection between the steel piles on ground and the foundation of the towers. The tower foundations can thus move against the layer of gravel strengthened by the steel piles. This new foundation concept extended here to earthquake-prone regions. The upper border of the load-bearing capa city of the strengthened foundations was developed by applying yield theory with appropriate kinematic mechanisms.

Non-linear finite element calculations were executed based on the above. The dynamic investigation of the bridge showed that the largest oscillations from earthquakes resulted in a multitude of cracks along the tower legs under the combined action of bending and tension. This cracked stage is, on one hand, helpful because it increases the flexibility of the legs below yield. On the other hand it is difficult to define precisely the cracked and uncracked regions during tower oscillations. As a consequence, 13 cross-sections were calculated in time steps of 0.02 sec which resulted in 130 000 different stages which all had to be investigated. An amplification factor made it possible to differentiate the individual steps by taking into account the behavior of the whole group of towers. At the same time the safety against progressive collapse of the whole group of towers was proved, in order to prevent a collapse of the whole bridge should one pier fail. The beam is continuous over the complete bridge length. At the towers an earthquake protection system is located transversely between the beam and the tower legs. It comprises dynamic dampers and hold-back systems with desired failure joints. These desired failure joints have to fail for earthquake forces above the highest wind loads in order to activate the hydraulic dampers which dissipate the energy and limit the transverse oscillations of the beam. The capacity of each of the four dampers at each tower comes to 3 500 kN in tension and compression. The relative movements between beam and towers during a designed earthquake reach ± 1.3 m with corresponding accelerations above 1 m/sec. For the approach bridges a combination of elastic isolators and hydraulic dampers was used.

Construction

Placing gravel layer

The particular difficulties for the construction of the piers are the large water depth of up to 65 m for the main piers, and the poor soils conditions. A combination of the latest technologies for off-shore oil platforms and submerged tunnels was used. The foundation works started with dredging the upper ground layer, placing a 19 cm thick layer of sand and ramming of the steel piles. The piles protrude 1.5 m above the sand layer and were covered with another 2 m thick layer of rounded river aggregates with a 50 cm layer of broken aggregates on top. This grading of gravel with decreasing inner friction from above to below provides the desired plastic behavior during earthquake. All these works were done from a 60 m long and 40 m wide floating platform which was anchored with chains to removable concrete blocks on the sea bottom. The equipment for piling was located on a submersible pontoon connected to one side of the platform with steel levers.

Foundations

The foundations for the towers were built in two steps near the city of Antirion. In a dry dock, 230 m long and 100 m wide, two circular foundations were concreted at the same time. The rear part of the dry dock had a depth of 8 m, the front part of 12 m. After completing the front foundation with a first pier section of 3.2 m the dry dock was opened by removing the front coffer dam and by towing foundation out. The second foundation was then towed forward and initially used to close the dry dock again. With this trick a lot of time was saved against the standard method of closing the coffer dam again. The construction of the pier shaft on top of the towed foundation was built in sections with jumping forms. After reaching the required height each foundation was towed to its final location and lowered onto the prepared gravel foundation. The whole foundation was then flooded in order to accelerate the expected settlements of 20 – 30 cm.

Towers

The four octagonal shafts were built in 4.8 m high sections with jumping forms. Heavy truss girders between the freestanding legs provided the required safety against earthquake during construction. The steel core for the cable anchorages in the tower heads was lifted in prefabricated units by a floating crane.

Beam

The composite beam was pre-assembled in 12 m long units, and the concrete roadway slab was cast on top, which is quite unusual. These 270 t elements were lifted by floating crane to the already built-in beam. The main girders were then connected with highstrength bolts, and the joints in the concrete roadway slab were closed with overlapping reinforcement and CIP concrete

Completed bridge

The Rion-Antirion Bridge represents a milestone in the development of cable-stayed bridges. Very difficult foundation conditions together with the high danger of earthquakes had to be overcome. Similar wide waterways may in the future be tackled with confidence following the example of the Rion-Antirion Bridge.

Excerpt from: Svensson, Holger Cable-Stayed Bridges, Wilhelm Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH, Berlin (Germany), ISBN 343302992X; pp. 418-425. References to figures and literature were omitted.