Irwell Street Bridge, Manchester -Salford.

BRIDGE OVER THE RIVER IRWELL FOR THE MANCHESTER AND SALFORD CORPORATIONS  - Amongst the various and important improvements that have recently been made in the city of Manchester is the erection of another bridge over the River Irwell, thereby increasing the means of communication with Salford, and relieving New Bailey street, Albert Bridge, Bridge-street, John Dalton-street, and Princess-street from the greater part of the heavy coal traffic and merchandise from the adjacent goods stations of the Lancashire and Yorkshire Railway. From the position of the bridge, and the requirements of the parties interested in the navigation, to preserve a sufficient headway, and the necessity for easy gradients for the approaches, it was requisite, in order to comply with the severe conditions respecting the thickness of the roadway platform, to display more than ordinary ingenuity in preparing the designs, so as not to impair the strength of the structure in any part. The bridge is slightly on the skew, one of the main girders being 130 feet and the other 127 feet in length; the width of the roadway between the parapets is 48 feet.

Owing to the heavy traffic the girders are of more than the usual strength and extra allowance is also made for the corrosion of the wrought iron, due to the exceptional atmospheric impurities which rise from the river. The main girders are on the bow-string principle, with double triangular lattice and vertical bars. They are 15 feet deep in the centre, the arch being a true parabola. The top and bottom booms are trough shaped, the top being composed of seven flange plates 9/16in thick, and the bottom of six plates of the same thickness, 3ft. 6in. in width, attached by four angle irons 4 inches by 4 inches by 5/8 in; to two rows of web plates consisting of two plate 2 feet deep by 5/8 inch thick, increasing in thickness towards the ends. Gusset plates are attached at intervals inside the two webs; and to these webs are riveted the diagonal and vertical bars. The rivets are 7/8 inch diameter, the holes in every case being drilled through the various plates in position, the holes in the outer plate being rimmed out and countersink. This was done by the contractor, who first marked the web carefully out, bolted a section of it together, and passed it forward under the radial drilling machines. The flange plates and angle irons were drilled in position by means of portable drilling machines having fourteen spindles.

The vertical struts are each composed of a flat plate between two T-irons braced together. The diagonals are also braced together to prevent buckling. The main girders rest on cast iron bed plates with gun metal strips, the bottom plate of the flange and the gun-metal strips being planed, so as to enable the girder to slide when expanding or contracting. Although different from the usual practice, this system has been found to act very well, as special notice was taken in the exceptionally hot weather which occurred during the construction of the bridge, the girders expanding and contracting to the extent of 5/8 inch.

The cross girders are 55 feet 6 inches long, 3 feet 5 inches deep in the centre and 2 feet 8 inches deep at each end. The flanges are curved both top and bottom at one end of the bridge and at the bottom at the other end, each girder varying in shape, owing to the required inclination of the roadway and the maintenance of the requisite headway over the river. The holes in the cross girders are all drilled in a similar manner to those in the main girders, and the work was riveted in the contractor’s yard. The cross girders are suspended from the main girder under each vertical by 24 inch bolts, 1 inch in diameter at each end. Each bolt was made in one piece without welding, and tested previous to erection with a dead weight of 4 tons.  After the bolts were screwed up the ends were rivetted over the nuts. The ends of the cross girders are surmounted by ornamental castings.

The distance apart of the cross girders is 8ft. 4 inches from centre to centre, and each one is capable of bearing a safe load of 50 tons in the centre. The roadway is composed of wrought iron curved plates 3/8 in. thick, supported on short longitudinal roadway girders rivetted to the cross girders, each of such girders being capable of bearing a safe load of 15 tons in the centre. The parapet is constructed of wrought iron boiler plates with diagonal strips rivetted over the joints, bolted to a cast iron moulded plinth. The whole is surmounted by an ornamental moulded cast iron capping with malleable iron spikes. The bridge is so designed that with the heaviest loads that can be brought on it no load will set up a strain in any part greater than 4.5 tons to the square inch either in tension or compression.

Nearly the whole of the iron is "Cleveland," and great care was taken in testing all the iron, both for its tensile strength and its elasticity. No iron was used that had a permanent set after 13 tons per square inch of tension was applied, or that broke with less than 24 tons to the square inch. The bridge was designed and executed under the direction of Mr J G Lynde, MlCE, Engineer to the Corporation of Manchester; the details having been worked out and the working drawings made by his assistant, Mr. Jerram. The contractors for the ironwork were the Stockton Forge Company, Stockton-on-Tees; and for the abutments, Messrs Ellis and Hinchliffe, of Manchester.

MANCHESTER CITY IMPROVEMENTS 1874 - The new street from Quay Street Manchester to Irwell Street Salford with the new bridge over the River Irwell is progressing satisfactorily; and it is expected by midsummer or autumn next year, the bridge will be opened to the public. The work in connection with it has been stopped by the frost. There will be a new road in connection with this from Water Street to Quay Street, coming out opposite St Mary’s Hospital. [Manchester Guardian 24 December 1874 page 6]

PUBLIC IMPROVEMENTS IN MANCHESTER 1876 - The new bridge leading through Irwell Street into Chapel Street Salford has been completed with the exception of the paving, which is to be proceeded with at once, so that in a few weeks we may expect to see the bridge open for traffic. It is anticipated that this thoroughfare will relieve New Bailey Street, Bridge Street, John Dalton Street and Princess Street of a considerable portion of the coal traffic by which they are now overcrowded, while at the same time it will be convenient to Salford people having business or pleasure in the Deansgate and Peter Street part of the city. The new bridge has been described as an iron girder of the “bow string” shape. The two main girders are each 130 feet in length and weigh 120 tons. The width from centre to centre of the main girders is 52 feet, and these rest on stone supports on each side of the river. The floor is of wrought iron riveted to the cross girders, and the whole structure has been erected with the view to the solidity and strength necessary for the heavy traffic which it will have to bear. [Manchester Guardian 7 December 1876 page 6]

Reference    The Engineer 6 April 1877 page 232 Illustrations page 233 and 236
Reference    Manchester Guardian 7 December 1876 page 6