Half Moon Lane Bridge (Gateshead)

Section of girder on display at the Discovery Museum, Newcastle

The lower portions of the wrought iron plates are badly corroded, and additional plates had at some point been welded over the corroded areas, attached to the original plates and to the top of the angle iron which connected the side and bottom plates

Note the cracks associated with the boss below the nut in the cast iron beam, and also porosity in the casting

This is a railway bridge crossing Half Moon Lane, on the approach to the High Level Bridge.

As built in 1848, it had an early and unusual form of box girder construction. Each box girder was made of riveted wrought iron plates. Sandwiched between these at the top was a cast iron beam, to which the plates were riveted. There were bosses at intervals along the cast iron beams to accommodate wrought iron hanger rods which supported cross beams carrying the deck. The nearby West Street Bridge was of similar construction, but of much greater span, with considerable skew. See here for detailed drawing of West Street Bridge. This shows that the transverse beams supporting the deck comprised wooden beams sandwiched between wrought iron plates, the assembly being riveted together. However the Half Moon Lane cross beams may have been of different construction. Decorative cast iron capping was fitted over the top of the flanges and on the outboard side of the bottom of the girders.

Due to the divergence of the street beneath the girders, one outer girder was of 75 ft span, while the other was only 35 ft, and there was a 55 ft girder in between. In 1982 the longer girder was removed and replaced, but sections were saved, while the 35 ft span girder was left in situ, but carried no load. This girder can still be seen from the road, revealing little of its unusual construction. A wider bottom flange seems to have been added at some point.

A section of the removed girder is on display Discovery Museum, Newcastle, although it is wrongly identified as being from the High Level Bridge. The thinness of the plates is readily apparent. They would have been stiffened at intervals by T-section bars riveted at the junctions between plates, between which were sandwiched diaphragm plates. The lower part of the wrought iron plates suffered badly from corrosion. On the inboard flank this was probably due to the retained moisture in the railway ballast, while on the outboard flank the responsibility probably lies with the retention of moisture behind the decorative capping. The photos show that at some point iron or steel plates had been welded over the damaged areas.

1848 REPORT '.... The new works leave the line of the old Brandling Junction Railway at the bridge over the High Street, Gateshead. Thence the line is carried upon an embankment, supported by retaining walls, for a distance of one hundred and sixty feet, when it crosses the new street leading from West Street to the end of the Half Moon Lane, by skew bridge of about forty feet span upon the square, at the height of about twenty-four feet from the surface of the road. It again runs along a short piece of embankment with retaining walls, to the Half Moon Lane, which is crossed by means of a bridge of new construction, the roadway being supported by three girders made of half-mch boiler-plate about seven feet in height. Upon each of these girders rests cast-iron beams, through which cast-iron [?] bolts of large size pass, descending through the girder, which forms a kind of hollow-box about fifteen inches in width, and giving support to iron transverse girders, upon which the roadway is laid. This bridge is thirty-seven feet span on one side, and seventy-five feet on the other, the height to the level of the rails, being nineteen feet. Another bridge on the same principle is in course of being constructed on the old line, a few yards from this, as a substitute for the wooden one which the trains daily pass ; the span of the latter bridge will be one hundred feet. Leaving the girder bridge above described, the line is carried upon nine arches of twenty feet span, with stone coignes the interior being of brick and cement; which arches terminate in a substantial block of ashlar masonry at the point where the High Level Bridge may be said to commence, the works already described constituting the approach thereto from the South. The line is thence carried over a platform supported by cast iron pillars, which rest partly upon sleeper walls, carried up to the height of the carriage roadway and also upon three semicircular arches of twenty-two feet nine inches span, and one of thirty-six feet three inches, the north abutment of the latter being at Pipewellgate, and from which the cast iron arches of the bridge spring the cast iron pillars are bound together at the top by longitudinal and transverse trough girders. Between this point and the river pier on the south side, the cast iron arch and road-way are nearly completed, and the second arch will be in progress in the course of a few weeks. .... .'

Note: The nearby West Street Bridge box girder bridge was constructed in 1849 by Robert Stephenson and Co.

See Also

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Sources of Information

• 'The influence of William Fairbairn on Robert Stephenson's bridge designs: four bridges in north-east England' by R. W. Rennison, Industrial Archaeology Review, Vol XX, 1998