RAILWAY ENGINEERING IN ENGLAND.

New Zealand Graphic, Volume XXXI, Issue VIII, 22 August 1903, Page 503

RAILWAY ENGINEERING IN ENGLAND.

By

C. E. ALLEN, A. I. Mech. E.

(Continued from last week.)

The Great Western Railway was opened to Maidenhead, a distance of 23 miles, in June, 1838; to Twyford, in July, 1839; the whole length to Bristol being completed by June 30th, 1841. An important work is the Wharncliffe viaduct, which carries the line over the valley of the River Brent, near Hanwell. It consists of eight semi-elliptical arches, each of 70ft span, with a rise of 17ft din. The average height from the ground level is 65ft. It is a fine example of brickwork, and is built throughout as light as possible, compatible with the most economical and effective distribu tion of material, a point to which Mr Brunel paid the most profound attention. This principle in brickwork forms somewhat of a contrast to the method

pursued in the earlier works of the Stephensons, whose fundamental policy was solidity. For example, in the case of retaining walls, Mr Robert Stephenson adopted the curved form, relying upon its shape and massiveness to resist the forward pressure of the earth. On the other hand, Mr Brunel’s plan was, in such structures as were subjected to earth pressure from behind, to make them as light as possible, and, in the case of retaining walls, to adopt the straight form, introducing, however, at the back, “sailing courses,” which were in reality projecting shelves. The pressure of the earth on these courses increased the weight at the back of the wall; in other words, increased the resistance to forward pressure.

Perhaps the finest example of a brickwork structure is the bridge carrying the railway over the Thames at Maidenhead, a view of which is given The bridge crosses the river, which is at this point about 290 ft wide, in two spans of 128 ft, with a rise of 24ft 3in.

Flood openings consisting of semi circular arches, one of 21ft span and three of 28ft span, precede and follow the main spans. The radius of curvature of the main arches, which are among the flattest ever built, is 165 ft, the line of pressure in each case being diverted in a downward direction by the thrust of the adjacent flat arches, which carry a mass of concrete. During the construction, when the centering was slackened, the brickwork

of one of the arches followed the centering for a distance of sin at about 15ft, one each side of the crown, and one of the spandril walls cracked, circumstances which at the time awakened the apprehensions of some with regard to the safety of the bridge. This, however, was remedied, and when the time came, years later, for the bridge to be widened, Sir John Fowler decided to carry the extra rails on brickwork, and by so doing preserved the elegance of the structure. Many other of Mr Brunei’s brick and masonry bridges on this railway are of an interesting character, but space will not permit more than a mention being made of the three-arched gothic masonry bridge near Bristol, with a centre arch

span of 100 ft; the flying bridge near Wes ton-super-Mare, with a clear span of 110 ft, carrying a road across the line at 60ft above the rail level: bridges of the same character used to keep apart the sides of a cutting; and skew ashlar masonry bridges with mechanically correct spiral tapering courses. Cast-iron as a materials for the construction of bridges was first use.l in railway work by the Stephensons. Brunel, however, did not make much use of it for this purpose, his objection to it reposing on the fact that repairs necessitated to such structures as a result of frosty weather or other causes were generally excessive. He introduced it, however, in eases where neadway was very limited in the form of troughing let into the crown of brick arches. His objections were also probably founded

on the fact that at that time sound castings of any large dimensions were not always possible to obtain. Wrought-iron, in spite of its cost, was a material Brunel employed in the larger of his bridges, as examples of which may be cited that carrying the Windsor branch of the Great Western Railway over the Thames, the Chepstow Bridge over the River Wye, and, finally, his last and culminating work, the Royal Albert Bridge over the River Tamar at Saltash. The structure at Windsor is a fine bridge on the bow and string girder principle. It has a span of 202 feet, and a truss of 23 feet in height. It crosses the river in an oblique direction, and a system of diagonal bracing connects the whole of the top of the trusses to strengthen the arched ribs. The greatest engineering achievement

ot Brum-l is the R >y.,l Albert Bridge, i iiis i- 22 in feet in length and 190 feet I igh. ami cro—es the river in two spans if 4.55 feet each, and on 17 side of minor dimensions. The piers are of masonry, that in the centre, on which are cast-iron columns supporting the main girders, being 35 feet in diameter. Each main span is arched in form, its chief members consisting of a wroughtiron oval tube. 16 feet 9 inches broad and 12 feet 3 inches in height, and two suspension chains falling from the extremities of the tube to a distance corresponding to the rise of the arched tube. The maximum distance between the tube and chains is 56 feet. Upright standards, connected by diagonal bracing, are interposed between tube and chains at 11 points in each truss, the girders carrying the road being suspended from each of

these at intermediate points. The total weight of ironwork in each span is 1060 tons, and the cost of the completed structure was £225,000. Advantage may be taken here of contrasting with the above bridge the masterpiece of Robert Stephenson, viz., that carrying the railway over the River Tyne at Newcastle, the last link which was to connect, by the East Coast route, the English and Scotch capitals. The bridge, which is a true example of a bowstring arch without cross-bracing, has six spans, each of 125 feet, which, as in the case of the Saltash bridge, combine both the arch and the suspension principles. The cast-iron arched ribs, four to each span, are arranged in pairs, the inner pair 2 feet 4 inches apart, a space of 6 feet 2 inches, utilised to form a footpath, separating each outer pair.

The tops of the arches support the gird ers carrying the railway, and wroughtiron vertical tie rods join up this to a lower flooring, which constitutes the carriage roadway and footpath passing under the railway. 4728 tons of cast-iron and .321 tons of wrought-iron were used, and the whole cost of the structure amounted to £24.3,000. Another well-known structure contemporary with the above, and by the same engineer, is interesting, from the fact that it was more or less experimental; its costly nature and high wind resistance causing its example, except in two instances, not to be imitated. Both the Britannia and Newcastle bridges may be said to represent an intermediate stage of bridge construction, the latter being the middle term between the arch and the beam, the former transition from the plate girder to the open girder type. In the Britannia bridge the plate girder is enlarged to form a tubular beam 15 feet wide, and with a varying depth of from 25 to 30 feet, the rails being laid along the bottom, one line of way in each tube. The supports consist of two abutments and three masonry piers, the central structure rising to a height of 2.30 feet. The bridge is split up into four spans, the maximum

being 460 feet, the smaller 242 feet, and the tubular beams were constructed to these lengths on shore, floated out on pontoons, and raised by hydraulic presses. Each section was united through the piers by shorter lengths being built in. The total cost of the structure was £601,865, which is equivalent to £.398 per foot run. In the Newark Dyke bridge, with a total length of 259 feet and a clear span of 240 feet 6 inches, on the Great Northern Railway, built in 1851-3, we have the earliest example of a Warren girder

bridge; but space will not permit a detailed description. The Forth bridge, so familiar as being the largest and most magnificent structure of its kind, is constructed on the canti lever principle, from designs by Sir John Fowler and Sir Benjamin Baker, Sir Thomas Bouch’s design for a suspension bridge across the Forth having been abandoned in consequence of the apprehensions awakened after the collapse of the Tay Bridge.

The structure consists of two main spans, each of 1710 feet, with a central pier on the rock of Inchgarvie. There are also two other spans of 675 feet each at the shoreward ends of the cantilever, fifteen of 168 and twenty-five of minor dimensions. The main piers are of masonry and concrete, with foundations in rock or boulder clay, the deepest being 70 feet below water level, with diameters of 53 feet at bottom and 49 feet at the top. The maximum distance from the highwater level to the top of the superstructure is 361 feet, and a clear headway is given of 150 feet. The cantilevers, constructed of the best Siemens steel, are on the double lattice-work system, and connected with one another by ordinary girders. The

columns over the piers are 12 feet in diameter and 120 feet apart at the base and 33 feet at the top, and to carry out this principle of offering an effective wind resistance, the cantilever bottom members widen out at the piers. All the main members in compression are tubes, while those in tension are of the lattice type, the stability of the whole structure being further increased by the addition of lattice girder wind bracing. To form some adequate idea of the vastness of the work it may be stated that the weight of steel in the main spans is 51,000 tons, and that 21,000 tons of cement, 47,000 tons of granite, and 113 000 tons of stone were used in the construction. The total cost, including that of the new railways necessary to form the connections with the North British Railway system, was £3,367,609.

The fact that this bridge, or indeed railway engineering at all as it is to-day, was rendered possible is owing to the introduction of cheap steel. In the form of steel rails it has lessened the prime c, st and increased the durability of the permanent way, and permitted speeus and train-weights which with the use of

iron rails would have been altogether impossible. Space will not "permit the tracing* of the development of the rail from its primitive form to the type at present in common use. but a diagram clearly sets out the essential details of the pattern and weighth of those employed on the Great Western Railway since the opening of the line. A brief reference must here be made to the Metropolitan and Metropolitan District Railways that run generally underground in and about London, an enterprise which perhaps did as much to establish the reputation of the late Sir John Fowler as the Forth Bridge itself. This progenitor of the underground systems of metropolitan transit was opened for a portion of its length in 1863. although the Inner Circle was not finally completed until twenty years later. The railway is, for the most part, in covered way, although tunnels proper and open cuttings with retaining walls occur in places. In the older portion of the line, designed to accommodate broad-gauge traffic, the covered way takes the form of an elliptical arch having a span of 28 feet 6 inches, and with a rise of 11 feet. The arch proper, which is laid with six rings, is supported by side walls 3

bricks thick and 51 feet high from rail level to the springing of the arch. The subject of effective ventilation while the use of steam locomotives has been the method of traction, is one that

has continuously been a source of trouble te the company and discomfort to the passengers. It is not, therefore, a matter of surprise that the companies concerned are taking steps to apply remedial measures by the substitution of electric traction. This is a measure which is both interesting and significant in that it may foreshadow what after all may happen in the course of time on many of our trunk lines in this country, namely, the supersession of the steam locomotive by electricity. In February, 1899, the associated companies voted £20,000 for the electrical equipment of 5000 ft of line between Earl’s Court and High-street, Kensington, on the insulated return system. The electrical conductors, of inverted channel steel, weigh 751bs per yard, and are carried on double insulators, the jar being taken by a piece of leather. The bonding is by copper strip hydraulically riveted. There are two positive and two negative feeders, lead-covered and armoured. The power house contains engines of 300 i.h.p. at 380 r.p.m., and the dynamos give 385 amperes at 550 volts.

There is only one train, and it requires current for about three minutes in every twenty; it has a motor ear at each end, but only one is used at a time. In the event of this type of train being adopted on the Inner Circle it would of course only want one motor car, because the trains always move in the same direction. Each motor carriage has four four-pole 26 x 25 Siemens motors, series wound, with armatures built on the axles. Each motor develops a normal draw-bar pull of 40001bs, the wheels being 47in diameter, and the maximum power about 200 h.p. Current is collected from the conductors by 14 (seven on each side) cast-iron shoes suspended from the bogies by insulated bolts. When fully loaded the train has started on a 1 in 43 gradient—■ a feat which an ordinary steam locomotive was unable to perform when hauling a similar load. Maximum speeds of 38 to 39 miles an hour have been reached.

In December, 1890. the City and South London Electric Railway was opened. This was the first example in the Metropolis of an underground railway system in which electricity was used as a motive-power. The success and popularity achieved by this line caused its example to be followed in the Waterloo and City electric lir". opened a year or two later. Space will just permit a brief notice of this line, which will serve as a representative of what promises to be a widely-adopted system in the Metropolis, as to-day the Central London Railway is in full work, and several other lines are either in actual course of construction or powers have been obtained. (To be continued.)