18i8.} 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



301 



ing' over, any point of the bridge. The proof was applied by 

 loading the bridge rib with 240 tons of rails, bars, &c. ; and it 

 produced the following satisfactory results, as the weight was 

 applied : — 



Weight in tons of rails, &c., 

 placed on ttie cross-girders. 

 g4i tons 

 61li „ 

 102 j „ 

 13? „ 

 171* .. 

 205i „ 

 240 „ 



Extreme amount of deflection 

 produced at centre of arch 

 l-lfii-ti inches. 



S-Sths „ 



1 5.1fith3 „ 



2 1 «lh „ 



2 .1 4th8 „ 



3 5-ieth« „ 

 3 11-lfiths „ 



The proof weight was fixed at 240 tons, as being double the 

 greatest load which the bridge can by any possibility be ever re- 

 quired to bear. A heavy goods' train weighs less than half a ton 

 per foot lineal ; a train, consisting entirely of locomotive engines 

 (which would be heaviest of all possible trains) would only weigh 

 ome ton per foot lineal, and, consequently, would place a load of not 

 more than 120 tons on a bridge of 120 feet span. The new bowstring 

 bridge has,therefore,been proved to twice the weight which ever can 

 be placed upon it, and to four times the weight which it is ever 

 likely to have to bear. It is scarcely necessary to add, that the 

 trial gave great satisfaction to all parties. These ribs are adapted 

 for large spans, in cases where either headway is of importance, or 

 where sufficient abutment cannot be obtained without very heavy 

 expense. Bridges constructed of these ribs may be employed 

 with perfect safety for very large spans, in precisely the same 

 manner as ordinary girders are used for small ones. The strength 

 of the bridge depends upon the rib or arch, and on the tie-bars 

 by which the extremities are held together. The vertical standards 

 Bxe introduced, partly to suspend the load from the arch, and 

 jmrtly to obtain longitudinal and transverse firmness ; they also 

 support the tie-bars. The diagonals are employed for the purpose 

 of preventing undue deflection in the rib, when the bridge is un- 

 equally loaded. The rib itself is constructed of boiler-plates and 

 aaigle-iron, rivetted up in the form of a square hollow trunk ; it is 

 strongly tied together, so that the fuU section of the plates and 

 angle-iron may be depended upon to resist the crushing strain. 

 In order to give this trunk additional lateral stiffness, the side- 

 plates, which form the top, overhang, and are strengthened on the 

 edges by angle-iron, &c. The tie-bars measure about 8 inches, 

 by 1 inch each, and are introduced in sufficient number to take 

 tJie whole strain. The ribs are supported at each end on cast-iron 

 shoes, fi.\ed at one end to the piers, and mounted at the other on 

 sliding-frames and rollers. This arrangement provides, not only 

 for e.\pansion and contraction, but also for motion under a very 

 heavy load. The action of these parts under proof has been found 

 to be perfect. Cross-girders, constructed entirely of wrought- 

 iron, are susi)ended between the ribs. 



Besides the above experiments on the Blackwall Extension 

 bridge, the two ribs for a bridge, 130 feet span, have been proved 

 with a weight of 260 tons — that is, 2 tons per foot lineal each, 

 prit on in dead weight, by suspending cast-iron cross-girders un- 

 dei'neath the points where the wrought-iron girders are intended 

 to be attached, and by placing thereon 260 tons of rails, pigs, bars, 

 &c. In proving, the load was first put on two points at one end, 

 tiien on the next two points, and so on, in order to produce as 

 nearly as possible the same effect as the passage of a heavily- 

 livaded train. In the case of one rib, the load was allowed to 

 remain several days, and then removed. After the lapse of a few 

 days, the same load was replaced, and again allowed to remain 

 some days. The results were satisfactory. 



During the process of proving, observations were taken with a 

 level, placed at a distance ; and the sinking of the bearing-plates 

 in the ground was observed and noted. The bridges being now 

 constructed, are intended to carry a double line of rails ; and the 

 test applied is, therefore, equal to 2 tons to each foot lineal of 

 single line of way. This test was fixed upon in the belief that 

 the greatest possible load which can in working be jilaced upon 

 e»ch line of rails is about 1 ton per foot lineal ; and that, to pro- 

 vide for the additional strain caused by the rapid motion, &c., of 

 the practical load of trains passing, the proof weight ought to be 

 fixed at double the greatest possible load. In very large spans, 

 (say 400 feet, and upwards), it would be necessary, on many ac- 

 cfmnts, to use four ribs, instead of two, and to brace all the four 

 ribs together overhead, so as to obtain additional transverse stiff- 

 ness. 



We understand that several girder-bridges of the above con- 

 struction are to be erected on the Blackwall Extension Railway, 

 under the superintendence of Joseph Locke, Esq. 



DRAINING MARSHES BY STEAM. 



The following paper, " On the application of Steam-power to tlie 

 Drainage of Marshes and Fen Lands," was read at the recent meet- 

 ing of the British Association, by Mr. Glvn. 



The number of districts in which I have successfully applied 

 the steam-engine to drainage is fifteen, and the quantity of land 

 so drained amounts to more than 125,000 acres ; the engines em- 

 ployed being 17 in number, and their aggregate power 870 horses, 

 the size of the engines varying from 20 to 80 horse- power. I was 

 also engaged in draining the Hammerbruk District, close by the 

 city of Hamburg ; and in another district near to Rotterdam, an 

 engine and machinery with the requisite buildings were erected 

 from my plans by the Che\'alier Conrad. In many of the swampy 

 levels of Lincolnshire and Cambridgeshire much had been done to 

 carry off the water by natural means ; and many large cuts had 

 been made and embankments formed — especially in the Bedford- 

 level, which alone contains about 300,000 acres of fen land ; and 

 the great level of the Fens contains about S80,000 acres, now rich 

 in corn and cattle. The Dutch engineers who had been engaged 

 in these works had erected a number of windmills to throw off' the 

 water when the sluices could not carry it away. By the aid of 

 these machines the land was so far reclaimed as to be brought into 

 pasture and cultivation, producing occasional crops of wheat. The 

 waters from the uplands and higher levels were intercepted by 

 catch-water drains, which carried away as far as might be practi- 

 cable the highland waters, and prevented them from running dowa 

 upon the fen ; but as it often happened, when there was most rain 

 there was least wind, and tlie wind-engines were useless when their 

 help vvas most needed, and the crops were lost. 



In this state was the fen country when the steam-engine was 

 introduced ; and by its aid the farmer may venture to sow wheat 

 upon these rich levels with as much confidence and even more than 

 upon higher ground ; for not only can he throw off at pleasure the 

 superfluous water, but in dry weather a supply can be admitted 

 from the rivers — so that farming in such cases is rendered less 

 precarious than in situations originally more favoured by nature. 

 It is, however, to be remarked that the quantity of rain which falls 

 in these levels on the eastern side of England being much below 

 the general average of the kingdom, the power required to throw 

 off the superfluous water is small compared with the breadth of 

 land to be drained ; the proportion seldom being greater than 10- 

 horse power to 1 ,000 acres, and in some cases considerably less. 



The general plan is to carry away the water coming off the 

 higher grounds, and as far as may be practicable prevent it from 

 running down into the marsh by means of the catch-water drains 

 before-mentioned, leaving the rain water alone to be dealt with by 

 mechanical power. As the quantity of rain falling in the great 

 level of the Fens seldom exceeds twenty-six inches, and about two- 

 thirds of this quantity is carried off by evaporation and absorption, 

 or the growth of plants, it is only in extreme cases that two inches 

 in depth require to be thrown off by the engines in any one month 

 —which amounts to 1^ cubic foot upon every square yard of land, 

 or 7,260 cubic feet to the acre. The standard and accepted niea- 

 suie of a horse's power is 33,000 lb. raised one foot in a minute, or 

 3,300 lb. raised ten feet in the same time ; and as a cubic foot of 

 water weighs 62;^ lb. and a gallon of water 10 lb., so a horse's power 

 will raise and discharge at a height of ten feet 330 gallons, or 52'8 

 cubic feet of water in a minute. Consequently this assumed excess 

 of 7,260 cubic feet of water fallen upon an acre of land will be 

 raised and discharged at an elevation of 10 feet in about two hours 

 and ten minutes. 



If the quantity of land be 1,000 acres of fen or marsh, with the 

 upland waters all banked out, the excess of rain, according to the 

 above estimate, will amount to 7,620,000 cubic feet. A steam-engine 

 of 10-horse power will tlirow off this water in 232 hours, or in less 

 than 20 days, working 12 hours a day ; and I have found this cal- 

 culation fully supported in practice. 



Although the rain due to any given month may fall in a few 

 days, yet in such a case the ground will absorb a good deal of it, 

 and the drains must be made of a capacity large enough to receive 

 and contain the rain as it falls ; — besides, in cases of necessity, the 

 engine may be made to work 20 hours a day instead of 12, until 

 the danger is past. I have generally caused the main drains to be 

 cut 7i feet deep, and of width sufficient to give them the required 

 capacity to receive the rain water as it falls and bring it down to 

 the engine. In some instances — where the districts are extensive 

 and their length great — it has been found requisite to make them 

 somewhat deeper. 



In all cases where I have found it necessary to use steam-power, 

 I have applied scoop-wheels to raise the water. These scoop- 



