The bridge over the Medway

Abstract

The new bridge over the Medway has to carry the new road from Dover to London, which has been built to help ease the summer traffic between these two points. The bridge is near Rochester. The structure was selected by means of a competitive award. Of all designs submitted, a reinforced concrete structure was chosen. The total structure is 1,000 ms long. The three main spans bridge the river. The centre span is 152 ms long, and the two adjacent ones are each 103 ms long. The approaches have 18 spans, with a total length of 654 ms. The bridge is 34 ms wide, and the roadway is divided into two lanes, each 7.30 ms wide. Two lateral ways, each 2.40 ms wide, are also provided. The bridge is very slightly curved in planform, and there is a slight slope between piles numbers 9 and 10. The abutments are of reinforced concrete. The one on the east side is cellular concrete, and the western one is made of mass concrete. The bridge foundations rest on reinforced concrete hexagonal piles, whose outer circumference has a 55 cms radius, and their length varies between 12 and 20 ms. When firm soil was at less than 6 ms depth, the piles were driven directly from the softer top layers. The bridge piles form portal frames, and have a variable height of 9 to 30 ms above the soil surface. The approaches form a continuous simply supported structure. Each span consists of 8 longitudinal beams, 30 to 41 ms in length, and weighing 190 tons each. They are prefabricated and prestressed. The main span in cantilevered, and consists of two overhangs, each 30 ms long, made up of box beams. Each of these beams has 8 webs, of 22 cms thickness, are covered by a slab, 22 cm deep, above, and are joined together at the bottom by another slab, whose thickness varies between 30 and 60 cms. The top slab forms the bridge deck, and overhangs 3.35 ms on each side of the structure. The depth of the central span varies between 10.75 ms over the piles and 2.75 ms at the crown. These beams have been prestressed both longitudinally and transversally. Between the two circulation roadways an elastic barrier has been placed, supported on metal posts.