A switch from pier and deck mounted cranes to use of the giant Taklift 7 floating sheerlegs from Smit International will substantially reduce construction risks for the Gefyra consortium currently building the dramatic 2.5km long Rion-Antirion cable stay bridge in Greece (Cover story April 01).

The decision affects the whole of the superstructure programme, now getting underway following successful immersion of the four giant caisson piers that support the bridge. They now stand in line across the narrow entrance channel to the Gulf of Corinth.

The Taklift will ferry out, and lift in, deck sections for the main cable stay spans, and will also lift into place the big steel box tower tops which contain the anchorages for the cables.

Originally it was planned to use 600tm Potain MD 600 tower cranes, one mounted on each of the piers, for positioning the steel tower top boxes. Small deck mounted sheerlegs would lift the deck units from barges.

The tower cranes were used for concreting and reinforcement steel in the ‘wet dock’ to build up the piers from the original 70m diameter pier footings created in dry dock, and they travelled with the piers to their immersion positions in the deep channel. Seawater ballast currently surrounds the crane towers, inside the hollow piers, while they are used above to further concrete the piers up to deck level 54m above the sea.

The tops of the cranes will be disconnected and moved sideways onto the completed deck level. It was intended that they would then be used for concreting on the pylon legs and for lifting into place the 11 steel boxes at the tower top. Each box is 2.7m wide, 7.5m long and 2.5m deep and weighs approximately 20t.

‘But for the four tops we would need a total of 44 lift operations,’ says Guy de Maublanc, project director for the French contractor Vinci (GTM Dumez) which is leading the seven strong Franco-Greek construction consortium. ‘And we discovered early that the channel is much windier than the shores.’

Finding enough calm days for the lifts – less than 13km/hour is needed – would be difficult. And the big Potain would need rigging with a short jib for the heavy lifts.

Taklift 7, even with a 160m long boom and 15m flying jib, will be able to lift 220t he says. That means boxes can be welded into larger units at the consortium’s north shore constructon yard, forming sections of six and four boxes, with a single box on the final top lift. A 158.4m under hook height will suffice for this operation at a 64m radius.

‘It means that we can have more controlled welding on shore. And there are just 10 lifting windows needed,’ says de Maublanc, ‘which is much more attractive.’

But that alone was not decisive. The Taklift will also be used to lift in the 27.2m wide deck units, this time rigged with a shorter 130m boom. At 49m outreach it will lift 390t, just enough for a fully concreted deck unit and its lifting tackle.

The original scheme was for the steel frames of the decks to be assembled by fabricator Cleveland Bridge on shore for barging out, where they would be hauled into place by twin sheerlegs mounted at the growing ends of the deck cantilevers. The deck would be concreted once in position. But the bridge location is a high risk seismic zone and each lift would have a relatively long period of exposure to earthquake risk. In contrast, the floating crane will be exposed to any shaking only at the point of connection of the new section, when a special quick connector mechanism takes the load. Hydraulic rams make final position adjustments.

Additional gains are that more shoreside work can be done with each deck fully concreted before it it is brought out. The Taklift will pick the units up directly, sailing four times a week into the now flooded dry dock where the tower bases were originally created.

‘The economics are good because we are working off two piers each way,’ says Guy de Maublanc. Four sets of smaller sheerlegs will not now be needed.