Tuesday, 30 December 2008

New Sleaford Lift Bridge

On a bitterly cold 29th December the bridge finally arrived in Sleaford! The crane arrived on site about 7.30 in the morning to set up, though I have to be honest that was before I arrived to view the events!
At first sight the bridge looked a bit like a giant Meccano Kit with two large artic lorries carrying all the parts. The first part to be unloaded was a large frame, a jig, for the bridge to be assembled on. This made sure that all of the parts were in the correct alignment for a quick and accurate assembly. First to be put in place on the assembly jig were the two ends. This was achieved with a few lifts from the crane and use of crowbars from Briton’s assembly team to sit the ends in the correct place. The second lorry was then unloaded with the counterweight, lifting deck and joining beams being put onto the ground next to the main assembly.

The next part to be assembled was the lifting deck. This had to be a very careful lift as the deck had to be lifted at an angle so that the pivot points had room to fit into the slots made for them in the end part. After one or two tries and some adjustment to the lifting strops to get the correct angle this was eventually achieved successfully.

The next stage was to lift the four joining beams and bolt them into place. This took place fairly quickly with the two beams on one side being lifted and bolted up closely followed by the two beams on the other side.

All this work took till lunchtime. Time for a quick sandwich and a warm up in the car! After lunch it was a case of a final tightening of all the bolts with an air spanner to prepare for the big lift. This was going to be best viewed from the New Street side of the river. Unsurprisingly a number of local Trust members were present at this time! Excitement mounted as we could see the assembly team placing the lifting strops onto the bridge and the crane swinging into position.

The crane revved up and the bridge, minus the counterweight, was lifted up and over the trees. This was quite a height, in fact, big as the crane was, it was nearly at its full reach.

The new abutments were ready to receive the bridge, the team having already removed the nuts from the anchor bolts. Despite one or two doubters who thought that the bolts weren’t lined up correctly, the bridge dropped into place with little fuss or effort and the lifting strops were finally removed.

The last big lift of the day was to put the counterweight into place. This was not part of the original lift as it would have contributed an extra four tons to the overall weight and would have made the lift very unbalanced. The assembly comprised mainly of bolting the pivot bearings to the main structure and fastening connecting rods from the counterweight arm to the end of the lifting span.

With the counterweight in place the final shape of the bridge was complete.

The only work that now remains to be done is to fit the mechanism to raise the bridge and also to make good the access walkways either side of the bridge. Both jobs should be happening by the middle of January.