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...shipping. Pier 10 comprises two concrete cylinders, 21 feet in diameter, surmounted by a reinforced concrete slab. This slab carries a hollow rectangular pier with rounded ends. There are three cross walls inside the pier, which is provided with ventilators and access manholes. The reinforced concrete roof is 4 feet thick and this carries the ends of the 100-feet girders and the swing span supports. Above the roadway is a massive concrete portal, providing an opening 18 ft. 9 in. high and 32 feet wide. The portal bears the arms of Fife, Stirling and Clackmannan carved in Portland stone. A gate, weighing nearly four tons, slides portcullis-fashion within the portal and is raised or lowered electrically. As the gate begins to drop, closing the bridge to traffic, a row of twelve red lamps is lit and a loudspeaker gives warning to "stand clear of the gate."
The gate begins its journey fast but a few feet from the road it gradually creeps into position, displaying to the traveller in letters of bronze the Clackmannan motto "Look aboot ye" advice well worth following with an engineering marvel before and the glorious Scottish scenery all round.
Pier 12, on the southern side of the central span, is built on reinforced concrete piles. In this instance it was found possible to use a steel cofferdam within which the piles were driven. The whole area of the cofferdam was plugged with concrete to a depth of 3 ft. 6 in. and, when this had set, and the cofferdam had been pumped dry, a concrete base was built on top of the plug round the piles. The base is 65 feet long, 27 feet wide and 7 ft. 6 in. thick.
The girders of the main 100-feet spans rest upon pier bearings that are alternately fixed and sliding. Each of the sliding bearings comprises a castiron bedplate 3 in. thick with a projecting tongue keyed into the concrete. This surface is faced with a phosphor bronze plate. On the underside of the girder is
attached a similar plate of steel to form the upper bearing surface. Alternate 100-feet girders are linked by 50-feet suspension girders, thus forming a system of cantilevers.
The steel was hauled from Kincardine Station, adjoining the north abutment, along the downstream track of the temporary bridge. The components of two contiguous girders, with their cantilever ends, were placed in position alongside one another on the downstream side of the bridge by two 5-tons locomotive cranes. These girders were then braced together and the whole mass of steel, weighing about 55 tons, was rolled by jacks to the upstream side of the bridge. This operation was carried out by the use of steel balls rolling in V-shaped tracks along the tops of the piers. Two more girders were then rolled into a central position and finally the remaining pair was placed on the downstream side to complete the series of six longitudinal girders between adjacent piers.
The reinforced concrete roadway, with its top layer of asphalt, was built on steel buckle plating between the tops of the girders. The cantilevered footways were provided with granite kerbs 8 in. high. Beneath the concrete paving ducts were arranged for cables and water pipes. The weight of steel used in the bridge amounted to 4,000 tons, and no fewer than 150,000 rivets were driven at the site.
The swing span at Kincardine, the longest in Europe, is a perfect combination of electrical and mechanical excellence. Despite its weight of 1,600 tons, the swing span is operated by electrical machinery at a trifling cost. This
machinery performs the turning and operates the gates and hydraulicgear on a consumption of only 2'1 units for a swing through an angle of 900 and back again.
Photo, General Electric Company, Ltd.
SLIP RING COLUMN in the machinery room ofthe swing span. The column is bolted to the fixed pivot round which the span rotates. Brush gear, rotating with the span, collects electric current from the rings, of which there are sixty. This arrangement of brushes and slip rings is generally adopted to supply electricity to rotating parts.
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