188 



RENNIE'-S BRIDGES. 



PART VII. 



wark Bridge, extending from Queen Street, Cannon 

 Street, to Bridge Street, South wark. It consists of 

 three cast iron arches, with two stone piers and abut- 

 ments. The arches are flat segments of circles, the centre 

 one being not less than 240 feet span (or 4 feet larger 

 than Sunderland Bridge, the largest cast iron arch that 

 had until then been erected), rising 24 feet, and spring- 

 ing 6 feet above high water of spring tides. The two 

 side arches are of 210 feet span, each rising 18 feet 

 10 inches, and springing from the same level. The two 

 piers were 24 feet wide each at the springing, and 30 feet 

 at the base. 



The works commenced with the coffer-dam of the south 

 pier on the Southwark side, and the first stone was laid 

 by Admiral Lord Keith about the beginning of 1815. 

 All the centering for the three arches was fixed by the 

 autumn of 1817, and the main ribs were set by the end 

 of April, 1818. The centres were struck by the end of 

 the month of June following, and completely removed 

 by the middle of October ; and the bridge was opened 

 for traffic in March, 1819. 



In the course of this work great precautions were 

 used in securing the foundations of the piers. The river 

 was here at its narrowest and deepest point, the bed 

 being 14 feet below low water of ordinary spring tides. 

 The coffer-dams were therefore necessarily of great depth 

 and strength to resist the pressure of the body of water, 

 as well as the concussion of the barges passing up and 

 down the river, which frequently drove against them. 

 Hence the dams were constructed in the form most 

 capable of resisting external pressure, and yet suitable 

 to the dimensions of the foundations. 1 The masonry 



1 They were made elliptical, and 

 consisted of two main rows of piles 

 14 inches square, placed 6 feet apart. 

 These were cemented together on each 

 side at the level of low water at half- 

 tide, and 2 feet above high water 



of spring tides, with horizontal wal- 

 ings or braces, also 14 inches square, 

 firmly secured to every tenth pile by 

 wrought iron screw bolts 2i inches 

 diameter passing through each row 

 of piles, and fixed at each end by 



