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Photo, Cleveland Bridge and Engineering Co., Ltd.
THE SUPERSTRUCTURE of the swing span of Kincardine Bridge comprises two enormous Warren girders. The roadway is carried on cross girders 5 feet deep. The weight at the centre is carried on two longitudinal girders 8 ft. 4 in. deep and on two transverse girders 11 feet deep.
...arrived for the use of sealed cylinders and compressed air.
The steel cylinders used for the first few piers were converted for use as compressed air chambers. The lower end of each was fitted with a coneshaped plate to form the roof of the working chamber. Leading up from this chamber two shafts, joined together longitudinally, were arranged. One shaft, smaller than the other, accommodated a steel ladder; the larger shaft permitted the hoisting
of buckets of spoil by the crane overhead. At the top of the twin shafts were arranged the air locks for the men and material. Compressed air was introduced into the shafts and between these and the outer casing water was pumped in to weight down the caisson.
It was possible with these caissons to work on the pier foundations in all conditions of the tide. They were first used at Pier 9, last of the "standard" piers on the northern section of the bridge, and work progressed shorewards to Pier 6. This course was adopted so that the travelling crane could use the central track. On completion of two adjacent columns this track was obstructed, for crane use, by the portal beams. With the removal of material from within the cylinders they sank lower and lower into the river bed, and water was excluded by air at a pressure of 18 lb. per square inch.
When the cutting edge of a cylinder had entered the bedrock excavation to a depth of about 3 feet, a plug of concrete was placed inside to form a foundation. This operation was carried out under air pressure and, to prevent the passage of air or water through the concrete during setting, pipes were run from beneath the lower edge of the cylinder to a point above the top of the plug. After the concrcte had set the pipes were sealed and the water ballast was replaced by solid material. The cone plate shafts and air locks were removed for use in another cylinder, and work proceeded on the concrete column within the plugged, open-topped caisson.
The corresponding piers on the opposite side of the river were built on piles of concrete reinforced by steel rods. The piles were 18 in. square, between 55 feet and 65 feet long, and weighed 9 tons. The reinforcing comprised four long steel rods joined with transverse links at close intervals; round the rods the concrete was cast in shuttering. A special pile-casting yard was laid out on the south bank of the river. The piledriver comprised a carriage 90 feet long, and the piles, protected by a steel helmet with a timber cap, were driven by a steam hammer weighing 5 tons. Six hammer blows were allowed for every inch of drive and the drop of hammer head was limited between the 3 ft. 9 in. and 4 ft. 3 in., according to the length of the pile. The weight on each pier was 1,250 tons, spread over eighteen piles. The number of reinforced concrete piles used was 484.
The building of the pile-supported piers began with the lowering of a cylinder, 14 ft. 6 in. in diameter, into the river bed for a distance of ten feet. Similar methods were used to those adopted for the piers close to the north bank of the river. This procedure permitted pile-driving within the caisson. After the driving of the piles a concrete plug was deposited, under water, in the bottom of the cylinder. When this concrete had set, the cylinder was pumped dry, leaving about 18 feet of each...
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