The length of the brick arches in the Surrey approach is 766 feet. Ditto Strand approach . 310 Length of bridge between the abutments 1380 Total length of bridge and brick arches . 2156 feet.
It should be mentioned as a proof of the excellent manner in which this noble structure has been executed, that on removing the centering, the greatest settlement did not exceed 1; inch, which is unprecedently small in arches of such great span. We shall now proceed to notice the New London bridge, erected by the present Mr. John Rennie, from the design of the late Mr. Rennie, his father, who died shortly before the work was commenced. According to the original plan, the new bridge was to have been built on the site of the old one, but the corporation of London decided that the bridge should be built 180 feet higher up the stream. The bridge was also made 6 feet wider, and the abutment arches carried 2 feet higher than in the original design. The foundations of the bridge were laid in coffer and the first pile for the dam of the south pier was laid March 15, 1824. As the works proceeded, it was found expedient that two of the small arches of the old bridge, on each aide, should be thrown into one, to compensate for the additional obstruction which the works occasion to the navigation of the river. This was effected with such skill, that the usual traffic was never once interrupted during the operation, the heaviest carriages passing over the bridge, and vessels passing through it, with the same facility as before ' • whilst such was the promptitude and despatch used, that the whole operation only occupied six weeks. The engraving on page 267, with the following description, will explain the manner in which the alteration was effected. The roadway was first boarded in and taken up one half at a time, and a space cleared away for the recep tion of a transverse iron girder A. A set of transverse timber principals B B was then laid on to this girder from the extreme piers of the two arches, bestriding, as it were, the central pier, which was to be removed • and these, instead of being placed at intervals as in roofs, were all fixed and bolted close together from one aide of the roadway to the other, forming one unbroken mass of timber. Above the girder
there was inserted what may not be unaptly termed the bresteummer C, into which the purr fins D D were mortised at intervals for the support of a substantial planking, on which the pavement was laid as before. The strength of the truss-work was farther augmented by a of counter-principals, as 1, 2, some of the struts being fixed close together, and others with an interval of one width between them. The bridge itself was nearly completed before the line of the approaches to it were decided upon ; it was at length finally settled that the approach on the London aide should com mence at Cannon-street, Eastcheap, passing over Thames-street by means of a dry arch, and that on the Borough side the road should form an inclined plane, supported on a series of brick arches, commencing near St. Thomas's Hospital, with a large dry arch facing Tooley street. On the 1st of August, 1831, the bride was opened to the public, the period occupied in its erection from the time of driving the first pile, being seven years, five months, and thirteen days. The engraving in the margin is an elevation of the new bridge ; it is formed of five semi-elliptical arches, the least of which is larger than any other elliptical stone arch ever before erected. The centre arch is 152 feet span, with a rise of 29 feet 6 inches above high water mark; the two arches next the centre are 140 feet in span, with a rise of 27 feet 6 inches; and the two abutment arches are 130 feet span, with a rise of 24 feet 6 inches ; thus the clear water way at all times of the tide is 692 feet, which is above 60 feet more than the old bridge afforded at high water mark. The whole length of the bridge from the extremities of the abutments, is 928 feet ; within the abutments, 782 feet ; and the width between the parapets is 53 feet. The engraving represents the new bridge.