Bonar Bridge
Old Bonar Bridge
Old Bonar Bridge consisted of two masonry arches of 50ft, and 60ft span with rises of 16ft. 8 in. and 20 ft respectively, and a main span of 150 ft. with 20 ft rise. The main span was a cast-iron arch, the lower member of which consisted of four open cast-iron ribs. The old bridge was commenced by Telford in 1811, and opened for traffic in November 1812, the total expenditure being about 13,000l.[1]
The contractors for the old bridge were Simpson and Cargill.
'..... at the close of the year 1811, about £2000 appeared to have been expended in building part of the north abutment, and in preparation for the rest of the masonry. The workmen in the quarries were not stopped by the winter season, and the foundations of the two piers were fixed in their places by means of caissons in the course of the summer, as also the south abutment on platforms, and the intermediate stone arches were successfully turned and secured. The iron-work was cast at the foundry of Mr Hasledine at Ponteyscylte, in Denbighshire, where, for the greater certainty, the arch itself was fitted together on temporary abutments and scaffolding in June last, and when found perfect in every particular, was taken to pieces, carried by canal conveyance to Chester, and shipped for the Dornoch firth, where it all arrived safe in the beginning of September : and the centering of the arch being already fixed and fitted for its reception, the iron castings were speedily re-constructed in their proper form, after which the upper part of the masonry, the roadway, and iron railing, was finished, and the whole bridge being completed in all its parts, was finally inspected and approved in the beginning of November last. The expedition by which the time specified in the contract was thus anticipated by a whole year, would in itself deserve some notice, but much more when the difficulty and magnitude of the undertaking is considered. The excavation under water, where the caissons were to be bedded eight feet under the surface of the gravel, easy operation and the alternate current and rapidity the tide, with the frequency of land-floods, opposed unusual obstacles to the formation of the wooden-centering, or temporary support for the arch. The latter especially called for and exercised all the the ingenuity and experience of Mr Simpson in such operations; nor could any strength or men and apparatus less powerful than that which he possessed as a masonry contractor on the Caledonian canal, have accomplished so great a work, as Bonar bridge, in little more than a twelvemonth. These favourable circumstances being previously known, appeared to us a full justification for undertaking a work otherwise hazardous, and at the same time for departing this instance from the usual mode of advertising for contractors and have good reason to know, that no advantage has been taken of the exception. In this bridge the road-way is supported by bearers of a lozenge form, which combine the advantages of internal strength with external appearance, and are not unworthy of a more particular description. We have therefore inserted in the appendix a view of the bridge, with plans and sections of its material parts, and Mr Telford's account of the structure of the iron arch, particularising the many improvements first introduced on this occasion. To conclude; we are assured, that both the masonry and iron work, of Bonar bridge is of the most substantial and finished kind, and that the whole structure, which will cost £12,000, bids fair to remain a monument of public munificence, and of judicious enterprize in the heritors Sutherland.' [2]
New Bonar Bridge (1893)
See illustrations.