Newark Dyke Bridge
Part of the Great Northern Railway.
The Original Bridge
The original bridge, erected in 1851-1853, was of an interesting design. It had pin-jointed Warren truss girders, and was one of very few pin-jointed permanent bridges installed in the UK.
The span between supports was 259 ft., the clear span 240½ ft.; depth between joint pins 16 ft. There were four girders, two to each line of way, i.e. two single line bridge structures sharing abutments. The girders' top flange consisted of cast iron hollow castings butted end to end, and the struts were of cast iron. The lower flange and ties were flat wrought iron links. This bridge was replaced in 1890 by a stronger bridge to carry the greater loads imposed by modern traffic.[1]
1853 'Newark Railway Bridge.— At the meeting of the Institution of Civil Engineers, on the 24th inst., the paper read was " A Description of the Newark Dyke Bridge, on the Great Northern Railway," by Mr. J. Cubitt, M.Inst.C.E. This bridge, for carrying the railway across navigable branch of the River Trent, near Newark, was described as being erected at point where the line and the navigation intersect each other, at so acute an angle, that although the clear space, measured at right angles, between the abutments, was only 97 feet 6 inches, the actual span of the girders was 240 feet 6 inches. The structure consisted of two separate platforms, one for each line of rails, carried upon two pairs of Warren's trussed girders, each composed of a top tube strut, of cast iron, opposing horizontal resistance to compression, and a bottom tie, of wrought iron links, exerting tensile force; these were connected vertically, by alternate diagonal struts and ties, of cast and wrought iron respectively, dividing the length into series of fourteen equilateral triangles, whose sides were 18 feet 6 inches long. The top tubes rested upon the apices of equilateral, or A frames, fixed on the abutments, and each pair of girders were connected by a horizontal bracing, at the top and bottom, leaving a clear width of 13 feet for the passage of the trains. Each tube was composed of twenty-nine cast-iron pipes, of 1½ inch metal and 13½ inches diameter at the abutment ends, increasing to 18 inches diameter with 2 5/8 inches metal the centre of the span,— the ends of the pipes accurately turned and fitted, so as to give exact contact of the surfaces, where they were connected together by bolts and nuts. The lower tie consisted of wrought iron links 8 feet 6 in. long, of the uniform width of 9 inches, but varying number and thickness, according to the tensile strain to which each portion was subjected; the abutment portions having each four links of 9 inches by 1 inch, and the centre piece fourteen links of 9 inches by 7/8 inch. The diagonal tie links varied from 9 inches by 1 5/16 inch to 9 inches by 3/4 inch, and, in order to accord with the relative strains, were distributed in groups of four, for the first three lengths from the ends, and then in couples for the next four lengths, on each side of the centre. The cast iron diagonal struts had a section resembling a Maltese cross, the area being in proportion to the compressive force to which they were subject. The bearing pins at all intersections were 5½ inches diameter, carefully turned and fitting into bored boles. The links of the lower tie were supported, in the middle of each length, by a pair of wrought iron rods, 1 1/8 inch diameter, suspended from each side of a joint pin traversing the top tube, and [by] nuts and washers they could be made to bear a portion of the weight of the platform of the bridge. The trusses were so arranged, that, all the compressive strains were received by the cast iron, and all the tensile force was exerted by the wrought iron; the proportions being such that when the bridge was loaded with a weight equal to one ton per foot run, which considerably exceeded - of train entirely composed of the heaviest locomotives used the Great Northern Railway, no strain could exceed five tons per square inch of section. The total weight of metal in each pair of girders, composing the bridge, was 244 tons 10 cwt., of which 138 tons 5 cwt. were cast iron and 106 tons 5 cwt. wrought iron, which, with 50 tons for the platform, &c, made the total weight of each bridge 204 tons 10 cwt., or 589 tons for the whole structure ; and the cost, exclusive of the masonry of the abutments, and of the permanent rails, but including the staging for fixing and putting together and the expense of testing, was 11,003l. In a series of experiments to test the stability of a pair of the trussed girders, at the works of Messrs.Fox, Henderson, and Co., where they were constructed, the following results were obtained. With weight of 446 tons regularly distributed, which was equal to 1½ ton per foot run, plus the weight of the platform, rails, &c., lowered seriatim on the thirteen compartments, the ultimate deflection in the centre was nearly 6 7/8 inches. With a weight of 316 tons, equal to 1 ton per foot run, plus the weight of the platform, &c., as before, the ultimate deflection at the centre was 4½ inches. When the bridge was fixed in its place, a train of waggons, loaded up to 1 ton per foot run, extending the whole length of the platform, caused a centre deflection of 2 3/4 inches. The deflection caused by two heavy goods engines, travelling; fast, and slowly, was 2 1/8 inches; and that produced by train of five of the heaviest locomotive engines used on the Great Northern railway, was 2½ inches. The proportions of the several parts of the structure were originally given by Mr. C. H. Wild (Assoc. Inst C.E.), and had been only slightly modified by the Author during the execution of the work.'[2]
From The Engineer, 7 March 1890: 'The main trusses were on the whole well constructed, the iron being of the very best quality and workmanship. The wind bracing at top and bottom was hardly in keeping with the main trusses, being badly designed and loosely fitted. The cause of the bridge wearing so badly was the manner in which the road was carried by the main trusses, cross timbers 8in. deep being placed across from truss to truss, and resting directly on the bottom tie, so that when the timber deflected during the passage of the trains all the pressure came upon the inner links, and as the links were fourteen in number at the centre, the leverage tending to cause rupture of the inner diagonals was considerable.'
By 1879 locomotive and train weights had increased considerably, and Richard Johnson ordered a thorough inspection of the bridge. 'It was then found that in consequence of the method of carrying the flooring, the inner links of the diagonals in the centre of bridge had elongated about 5/16 of an inch, thereby putting all the stress on to the outer links. The method of laying the floor was then altered, and arranged in such a manner that all the members did their share of the work that was required of them. In 1888, fresh signs of weakness occurred, and as they were beyond the possibility of a remedy Mr. Johnson decided on a reconstruction, and with that end in view instructed his assistant, Mr. E. Duncan, to prepare designs for a new steel structure.'
The 1890 Bridge
The 1890 bridge was constructed by Andrew Handyside and Co. The design of the bridge and the process of installation were described in The Engineer.
'The design of the new bridge is of the class of truss known as the "Whipple-Murphy"type, and is made entirely of steel, the steel used being made by the basic process. Upwards of 400 tests were made during manufacture at the Staffordshire Steel and Ingot Iron Co.'s works, near Wolverhampton, and also by Mr. David Kirkaldy, the tests in all cases showing remarkable uniformity. ..... As the new bridge could not be constructed in situ, a staging had to be formed about 600ft. long, and parallel with the old one; in order to do which piles varying from 30ft. to 38ft. in length had to be driven by the side of the embankment and across the river. The piles were driven five abreast, two outer ones 5ft. apart carrying longitudinals, the full width of the stage being 33ft. Upon this stage the girders were constructed between two lines of rails ..... upon which twenty-four trolleys were placed, twelve on each side, each trolley having an hydraulic jack in the centre. These trolleys were divided into four sections, and connected up; struts and ties were then fixed on the top of each jack. Each section of jacks was connected by a pipe passing along the length of that section, a connection being made with all the six jacks. These pipes were fed from four small pressure pumps, one placed in each section. By this means the pressure was applied simultaneously in all four sections and the whole bridge lifted and carried by the twenty-four jacks, the whole bridge was then moved forward upon the trolleys, .......
...... The next operation was to get the old bridge off the cast iron frames .... two jacks, each capable of lifting a hundred tons, can be seen [see Fig. 3 above] placed under the end strut. Four of these were used, two to each truss. Tho bridge was then lifted 3in. and the cast iron frames removed, and the lifing proceeded with until it was 20in. above its old position. A timber trolley, ... was then fixed, and the jacks moved to the other end and the same operation carried out. When both ends were lifted and securely fixed to the trolleys, the bridge was hauled out sideways, ......
The description of the new bridge continued in The Engineer, 21 March 1890, from which: 'In the main trusses all the bracing bars are 3/4in. thick, and connected with the top and bottom members by two fishplates, the difference in area being made in the width. The bracings in struts are made from bars 2½in. by 3/8in. The cross girders are suspended to the main trusses by plates at each end, the plates passing through a slot cut in the flange plates and rivetted to cross-plates at the lower end of struts of main trusses, by this means all the connecting rivets are in shear and the load hangs directly from the axis of main truss. The bottom wind bracings are made with flat bars rivetted to ends of cross girders. The top wind bracings are, on account of three-quarters of the total wind press ure passing through them, much heavier, and are made of four angle irons with bracing. [Fig. 6 above] shows the gib and cotter connection in counterbraced bars made from flat bars bent round and cut to shape. .... Both bridges have been tested with the heaviest load that could be put upon them, that is, six locomotives, .... making a total load of 396 tons. The amount of deflection in the centre from this load was 1 7/16in., with a lateral movement of 1/20in. during the passage of a train at thirty miles per hour, and the maximum stress at any point is equal to 6½ tons per square inch.'
2000 Bridge
The 1890 bridge was replaced in 2000 by a steel bowstring bridge of 77m span, suitable for 140 mph trains. Structural design: Cass Hayward and Partners Ltd. Sunstructure design: Corus Rail. Main contractors: Skanska Construction UK Ltd. Structural steelwork by Cleveland Bridge.
The bridge is carried on new outboard foundations to avoid uncertainties associated with re-use of the existing abutments on timber piles. The new bridge is square spanning, rather than skewed.
The bridge was prepared to allow it to be slid into place during the August 2000 Bank Holiday railway possession. This was successfully achieved, along with re-alignment of the tracks and erection of new overhead electrification masts, well within the permitted 72 hours.
See Also
Sources of Information
- ↑ [1] Encyclopaedia Britannica 11th Edition: Bridges. See Fig. 19
- ↑ Lincolnshire Chronicle - Friday 3 June 1853
- ↑ [2] Steel Bridges - A Practical Approach to Design for Efficient Fabrication and Construction by Alan Hayward, Neil Sadler and Derek Tordoff: Newark Dyke Rail Bridge Reconstruction over the River Trent. BCSA Publication No. 34/02