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On-site assembly

STEEL

ROWECORD is not just responsible for fabrication of the bridge, it must also put all of the pieces together on site and raise it up to its final position 'We are due on site after Christmas. The work requires one of the largest cranes in the country. It comes to site on the back of 42 articulated lorries, ' says Mr Dale.

First up is the backstay, which is dropped into place on the mast base and held in place by a system of temporary props. It can then be detached f rom the crane, wh ich then goes to pick up the front stay. Yet despite its massive size the 1,200-tonne Gottwald crane does not have the reach to place the front stay at its final position, at 35 deg to the horizontal facing out into the river. Instead it is installed at 15 deg to the vertical on a rotating pin base. Strand jacks are then attached back to the temporary props and the front stay is slowly allowed to rotate out to its final position. During this process, once it has reached about 25 degrees f rom vertical, the cables that will hold up the bridge are attached.

They cannot be attached any earlier as they are extremely stiff and over-bending would cause the coil locks to break.

With the forestay close to its final position the cable will begin to take up the tension, pulling the backstay off the temporary work.

The second stage of erection involves fitting the deck. The first section to be installed is the centre of five bridge deck sections. The deck section is dropped below the front stay and then brought up so that it can be attached to the cables.

Once in place it is also t ied back to the bankside to prevent it moving while the other sections are attached. Two more sections are attached to link the deck back to the bank, fixing it in position. The crane can then be repositioned to install the two other sections that land on the other side of the river.

During erection the whole structure is held together by a series of bolts but once the cables are tightened, essentially tuning the bridge, these joins are welded to provide permanent strength.