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Keeping them in suspense Northern Greece is full of gorges slicing across Egnatia Odos' alignment.

To meet the challenge of building dozens of bridges, contractors have made widespread use of the Italian Carroponte construction system (see diagram).

All bridges built with the system are two lane dual carriageway. Pairs of hollow box section reinforced concrete piers are built using crane- lifted formwork.

On one of six ravine bridges being constructed by Aktor-Ergas joint venture at Kavala the piers are 55m high. To anchor them securely in this seismically active region 10m deep circular rock-sock foundations have been used making the piers vertical cantilevers.

While pier construction is carried out, prestressed concrete beams are cast in a yard set up on the approaching road. There are two beams to each span and each can be as deep as 2.8m and weigh up to 130t.

Beams are 'picked up' into a giant launching girder. This is jacked forward until it straddles an unbridged span, its front end supported by a pier.

During jacking the beam acts as a counterbalance to the weight of the girder's unsupported front end. Once the launching girder is in position, though, the beam is moved along the girder and lowered into position. The girder is then moved back to the casting yard to pick up another beam.

After both beams have been laid across a span, precast panels and edge elements are craned into position.

Reinforcing is laid above these and concrete poured, leaving no deck joins. Csepreghi describes the system as 'elementary and functional'.

Spun like a spider's web across the Metsovo valley in the Pindus mountains, will be a 500m long towerless suspension bridge.

The rock-anchored design by UK architect Chris Wilkinson with engineer Ove Arup won a competition for a 'showpiece' crossing.

Chris Wilkinson partner Tim McDowell contends the exclusion of pylons served both technical and aesthetic ends. A suspension bridge with minimal visible support minimises the impact on a place of outstanding beauty.

Earthquakes have rocked Greece with damaging effect this century. Technically, suspension bridges perform well in seismic regions. Difficulty in getting plant and materials to the valley floor pointed towards a solution that required minimum access. Eliminating pylons removed a major cost. And access to the points at which the cables will be anchored is relatively easy, McDowell says.

Swiss architect Christian Menn and German engineer Schleich Bergmann teamed up to win the competition for a 940m long bridge spanning the Arachthos valley in the western section.

Because the valley may be flooded to a depth of 50m if a proposed hydroelectric scheme goes ahead, the design had to work visually as a tall structure above land and above water. Menn/Schleich Bergmann proposed a crossing of 11 spans. Piers are 'ladders' of reinforced concrete branching into a 20m tall Y which supports the deck. Height from ground to deck is 76m. Construction will be balanced cantilever.

A third design competition is to be held for the crossing of the protected Nestos wetland area in eastern Greece, where the cost of tunnelling would be exorbitant. A beautiful bridge may win over environmentalists.

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