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A description of the Newark Dyke Bridge, on the Great Northern Railway
156
Civil E~g~neering.
in gu~t:a percha~ and protected in the ~sual manner by an outer covering. of iron wire. It could noL be la.id, as was intended~ during the previous week, owing to tim gales from the east preventing the opening ofthe dock gates at Sunderland to let the vessel containing it pass out. As several prewous attempts to lay a submarine telegraph across the Irish Channel had failed, every tare was taken to ensure the successful termination of the present attempt; and the expedition, consisting of the screw steamer William Hurt (with the cable and apparatus on board), the Conqueror, and the Wizard, left the Irish coast, ha~ ing landed the end of the cable at a point about two miles to the south of Donaghadee harbor, and commenced the submersion of the cable, under the guidance of Captain Hawes, R. N., specially appointed by the Admiralty, who rendered great assistance in determ(ning and directing the exact course to be pursued. The cable was landed on Wednesday morning~ in a sandy bay (called Morn bay), a little to the north of Portpatrick.
.~ Description of the Newarlc Dyke Bridge, on the Great Norlhern Rail. way. By Ma. J. Cu~ITT, M. Inst. C. E.* 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-tubed strut, of cast iron, opposing horizontal resistance to com. pression, 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 a series of fourteen equilateral triangles, whose sides were 18 feet 6 inches long; the actual span of the girders being 240 feet 6 inches. Each tube was composed of twenty-nine east iron pipes, of 1.~ inch metal and 13½ inches diameter at the abutment ends, increasing to 18 inches diameter with 2~ inches metal at the centre of the span. The lower tie consisted of wrought iron links 8 feet 6 inches long, of tile uniform width of 9 inches, but varying in number and thickness, according to the tensile strain to which each portion was subjected. The diagonal tie links varied from 9 inches by 1-1~5inch to 9 inches by ~ inch. 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. "['he total weight of metal in each pair of girders, composing the bridge, was 244 tons 10 c w t , 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 294 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 a weight of 446 tons regularly distributed, which was equal to 1~ ton per foot run, plus the weight of the platform, rails, &c., lowered seriatim on the thirteen compartments, the ultimate From the Journal of the Societyof Arts, Lol~don,No. 27.
Iron Roofs of Large STan.
157
deflection in the centre was nearly 6~ 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 4} inches. When the bridge was fixed in its place, a train of wagons, loaded up to 1 ton per foot run extending the whole length of the platform, caused a centre deflection of 2~ inches. The deflection caused by two heavy goods engines, travelir~g fast, and slowly, was 2~- inches; and that produced by a train of five of the heaviest locomotive engines, used on the Great ~orthern Railway, was 2~- inches in the centre.--Proc. Inst. Cir. Eng., ~ay 24, 1853.
~.on Roof~ of Large Spa~,*' (From a paper by ~¢[r.Robert H. Bow, C. E., of Edinburgh,read at the RoyalScottish Societyof Arts.) After some introductory remarks, and insisting upon the propriety of employing roofs of great clear span for principal railway stations, the author institutes a comparison between the diilbrent classes of structures employed for the principals of roofs; and deduces that the triangular frame (in which the rafters constitute the main compressed member of the fabric) deserves to be preferred before all arched, compound, or other forms, when an inclined surface is demanded by the covering, of the character required for slating. And he further shows, that where uniting or abutting principals carl be used, rafters, when made straight and treated as bridges, form principals of a very economical character; but that, tbr such a situation, rigid arched structures are quite inadmissible. He arranges those straight-raftered principals in which the rafters are the main compressed members, into two classes; the first class embracing those which are tied, or exertonly vertical pressures on the supports; and the second, those which are untied or of the abutting character. The principals of the tied class are of two kinds; in the principals of the first variety each rafter acts as a bridge; but the principals of the second partake of the nature of a framed girder. The designs proposed by Mr. Bow, are of the former variety~that is, each rafter is treated as a bridge, and they may therefore be employed either in the tied or in the untied state. In order to test their merits as suitable forms for long spans, they are compared with the' best form at present in use for long spans, and which is of the latter or girder character. In the calculations undertaken in order to make the comparisons, the weight of each part is represented by the product of the successive multiplication of its length by its strain, and the allowance of metal per ton of strain. For ties, the sectional area of metal is estimated at one-eighth of a square inch; for rafters at a quarter of a square inch; and for the struts of the bracing at half a square inch for each ton of strain. The accompanying tables give the results of his ca]culatlons. In these, however, the effect of that source of economy of material which arises from the peculiar fitness of the proposed forms tbr cases requi!'ing.many supported points, is alone made evident. But if the stra, ns m the struts of the several forms be compared, it will be found that the strains * From the LondonMechanic'sMagazine,June, 1853. ¥o~. XXV!.--'ruI~1) SmtlXS.--~No.3.--S~:~e-r~:~:~t:It,185~. 14
Civil E~g~neering.
in gu~t:a percha~ and protected in the ~sual manner by an outer covering. of iron wire. It could noL be la.id, as was intended~ during the previous week, owing to tim gales from the east preventing the opening ofthe dock gates at Sunderland to let the vessel containing it pass out. As several prewous attempts to lay a submarine telegraph across the Irish Channel had failed, every tare was taken to ensure the successful termination of the present attempt; and the expedition, consisting of the screw steamer William Hurt (with the cable and apparatus on board), the Conqueror, and the Wizard, left the Irish coast, ha~ ing landed the end of the cable at a point about two miles to the south of Donaghadee harbor, and commenced the submersion of the cable, under the guidance of Captain Hawes, R. N., specially appointed by the Admiralty, who rendered great assistance in determ(ning and directing the exact course to be pursued. The cable was landed on Wednesday morning~ in a sandy bay (called Morn bay), a little to the north of Portpatrick.
.~ Description of the Newarlc Dyke Bridge, on the Great Norlhern Rail. way. By Ma. J. Cu~ITT, M. Inst. C. E.* 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-tubed strut, of cast iron, opposing horizontal resistance to com. pression, 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 a series of fourteen equilateral triangles, whose sides were 18 feet 6 inches long; the actual span of the girders being 240 feet 6 inches. Each tube was composed of twenty-nine east iron pipes, of 1.~ inch metal and 13½ inches diameter at the abutment ends, increasing to 18 inches diameter with 2~ inches metal at the centre of the span. The lower tie consisted of wrought iron links 8 feet 6 inches long, of tile uniform width of 9 inches, but varying in number and thickness, according to the tensile strain to which each portion was subjected. The diagonal tie links varied from 9 inches by 1-1~5inch to 9 inches by ~ inch. 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. "['he total weight of metal in each pair of girders, composing the bridge, was 244 tons 10 c w t , 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 294 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 a weight of 446 tons regularly distributed, which was equal to 1~ ton per foot run, plus the weight of the platform, rails, &c., lowered seriatim on the thirteen compartments, the ultimate From the Journal of the Societyof Arts, Lol~don,No. 27.
Iron Roofs of Large STan.
157
deflection in the centre was nearly 6~ 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 4} inches. When the bridge was fixed in its place, a train of wagons, loaded up to 1 ton per foot run extending the whole length of the platform, caused a centre deflection of 2~ inches. The deflection caused by two heavy goods engines, travelir~g fast, and slowly, was 2~- inches; and that produced by a train of five of the heaviest locomotive engines, used on the Great ~orthern Railway, was 2~- inches in the centre.--Proc. Inst. Cir. Eng., ~ay 24, 1853.
~.on Roof~ of Large Spa~,*' (From a paper by ~¢[r.Robert H. Bow, C. E., of Edinburgh,read at the RoyalScottish Societyof Arts.) After some introductory remarks, and insisting upon the propriety of employing roofs of great clear span for principal railway stations, the author institutes a comparison between the diilbrent classes of structures employed for the principals of roofs; and deduces that the triangular frame (in which the rafters constitute the main compressed member of the fabric) deserves to be preferred before all arched, compound, or other forms, when an inclined surface is demanded by the covering, of the character required for slating. And he further shows, that where uniting or abutting principals carl be used, rafters, when made straight and treated as bridges, form principals of a very economical character; but that, tbr such a situation, rigid arched structures are quite inadmissible. He arranges those straight-raftered principals in which the rafters are the main compressed members, into two classes; the first class embracing those which are tied, or exertonly vertical pressures on the supports; and the second, those which are untied or of the abutting character. The principals of the tied class are of two kinds; in the principals of the first variety each rafter acts as a bridge; but the principals of the second partake of the nature of a framed girder. The designs proposed by Mr. Bow, are of the former variety~that is, each rafter is treated as a bridge, and they may therefore be employed either in the tied or in the untied state. In order to test their merits as suitable forms for long spans, they are compared with the' best form at present in use for long spans, and which is of the latter or girder character. In the calculations undertaken in order to make the comparisons, the weight of each part is represented by the product of the successive multiplication of its length by its strain, and the allowance of metal per ton of strain. For ties, the sectional area of metal is estimated at one-eighth of a square inch; for rafters at a quarter of a square inch; and for the struts of the bracing at half a square inch for each ton of strain. The accompanying tables give the results of his ca]culatlons. In these, however, the effect of that source of economy of material which arises from the peculiar fitness of the proposed forms tbr cases requi!'ing.many supported points, is alone made evident. But if the stra, ns m the struts of the several forms be compared, it will be found that the strains * From the LondonMechanic'sMagazine,June, 1853. ¥o~. XXV!.--'ruI~1) SmtlXS.--~No.3.--S~:~e-r~:~:~t:It,185~. 14