water, a most important matter in the supply of drinking-water, where there is any special liability to cholera or other endemic diseases. The cost of cement tubes is not more than about 40 per cent. of that of iron pipes. The work carried out for the municipality of Cuneo consisted in the extension of their supply, in order to provide the newer and higher parts of the city with a sufficient quantity and pressure of water. The old supply is conveyed in an open channel through a tunnel or subway, 5 feet 11 inches in height, to the crown of the arch, and 2 feet 3 inches in width. This tunnel is made use of for the main length of the new pipes, which are laid on the floor-level and over the original channel, which is arched over by the new work. The lower channel is retained for all general purposes-street-watering, baths, washhouses, &c., while the new cement-tube conveys the water for drinking purposes. There is a fall of 77.8 feet in a length of 1,973 yards, the average inclination being, therefore, about 1 in 76. The new supply having to be under the full pressure due to this total fall, the Author, before commencing the work, undertook various experiments to determine the proportions to be given to the tube. According to the usual formula, the tube, having a diameter of 97 inches, with head of water as above, would require a thickness of 7 inches; but, by a series of careful experiments, it was found that a thickness of 3.15 inches was amply sufficient. The material employed was Casale cement, and the cost (including labour) was found to be about 58. per lineal yard. Inclusive of all contingent charges, the cost of the work as executed was 68. 9d. per yard. Owing to the confined space in which the work had to be carried out, advantage was taken of four manhole shafts to start work simultaneously from all the different faces, and the materials were conveyed along the tunnel on small trollies. The work was entirely completed without interference with the old supply in the open channel. The cement was set over this channel on a curved iron plate, which served as a centering until the material set, while the sides were moulded between larch frames wedged as necessary. consisted of an expanding iron cylinder. Each mixing of material, which was done on the spot, made sufficient for a length of 6 feet 6 inches. During the winter the cement set in twelve hours, but later, when two qualities of cement were blended, the setting was perfect in less than seven hours. The core P. W. B. The Bridge over the Arkansas River at Van Buren. By C. D. PURDON. (Transactions of the American Society of Civil Engineers, vol. xx. 1889, p. 151.) This bridge has a total length of 1,798 feet, consisting of three spans 252 feet 9 inches each, four spans of 162 feet each, and a swing-bridge 366 feet long. The main girders are of the American pin type, but the top chords rise towards the centre, and thus resemble the double-span girder of the swing-bridge. The bridge has a single line of railway, the platform resting on six longitudinal stringers, of which the two outer ones do not carry the train in its usual position. The Paper gives a full account of the history of the erection of the bridge, weights and quantities of materials, and the specification for the contract of the work, which is as complete as American specifications now usually are. M. A. E. The Sibley Bridge. By O. CHANUTE, J. F. WALLACE, and W. H. BREITHAUPT. (Transactions of the American Society of Civil Engineers, vol. xxi. 1889, p. 97.) For the purpose of extending the railway from Kansas City to Chicago, the crossing of the Missouri could be effected in a direct way at Sibley Point, or in a north and south direction at Sibley Reef, lengthening the line by 1 mile. The latter point, however, was chosen on account of a lesser probability of a change in the bed of the river, on account of a smaller width of the river by 550 feet, and on account of a greater height of the bed rock by about 10 feet, viz., 30 to 40 feet below low water. The bridge is 2,000 feet long, in seven spans, as follows: 200, 400, 400, 400, 250, 175, 175. The 400-feet spans are over the river, giving a clear height of 50 feet above the high-water mark of 1844, the railway being on the bottom flange. In the other spans the railway is on the top flange of the girders (deck-spans). The piers are of limestone masonry, the base of the largest being 63 feet 9 inches x 27 feet 5 inches, with a pressure of 7,600 lbs. per square foot on the rock from all loads. The foundations of the piers between the second and the seventh span were made with the pneumatic method; the sinking of the timber caissons began on March 23, 1887, and the last pier was completed on December 15 of the same year. The erection of the iron superstructure, for which the contract was let to the Edgemoor Iron Company on January 15, 1887, began on July 27, 1887, and was completed on February 11, 1888. The 400-feet span girders are of the familiar American pin type, composed of riveted top chords, posts and struts, and of forged bottom chords and diagonals (eye-bars). The diagonals are inclined at an angle of about 45°, intersecting the posts in the middle; the depth of the girders is 50 feet between pins and the panel-length 24 feet 9 inches. The width between centres of trusses is 21 feet for a single line of railway. Besides the ordinary rail-bearers directly under the rails, and calculated with the full load, there is a second pair 9 feet 2 inches apart, calculated with half the load. The sleepers are 16 feet x 8 inches x 8 inches, and are spaced 14 inches between centres. There is an inner iron guard-rail, and an outer oak rail protected by an angle-bar. The top chords, including the rivets, the bottom chords and the diagonals are of steel; the intermediate posts and struts are of iron. The quantity of steel in each 400-feet span is 718,751 lbs., and the quantity of iron 513,947 lbs. ; the weight of timber floor with rails is 480 lbs. per foot lineal. The moving load consists of two Consolidation engines of 172,000 lbs. each, on a base of 55-feet length, followed by a train of 3,000 lbs. per lineal foot. The wind pressure is taken at 30 lbs. with the train-load and 50 lbs. without it; in both cases two surfaces of one truss have been calculated. In proportioning the sections the Launhardt formula = was used for the 400-feet spans, but not for the smaller spans. For the steel bottom chords 8 was assumed 12,000 lbs. for stresses from the load, and = €15,000 lbs. for stresses from windpressure. For riveted members in tension s was taken one-seventh less. For compression members, 8 = 10,000 lbs. for steel end-posts and top-chords, 8,000 lbs. for iron intermediate posts, and 12,000 lbs. for iron struts, multiplied, however, with the factor as above, and then put into the formula where a = 40,000 for columns with two flat ends, a = 30,000 for columns with one flat end, and a = 20,000 for columns with two pin ends. Flanges of floor girders 6,000 lbs. per square inch, webs 4,000 lbs. per square inch, rivets and pins in shear 7,000 lbs. per square inch, rivets in situ and in floor-beams 5,600 lbs. The bearing area of pins and rivets to be proportioned to 12,000 lbs. per square inch, and the bending strain in pins not to exceed 15,000 lbs. on iron and 20,000 lbs. on steel. The pressure on the granite bed-stones not to exceed 250 lbs. per square inch about 16 tons English per feet superficial. The pressure on the longitudinal inch of expansion rollers of d inches diameter not to exceed 540,000d lbs. = These data are followed by a specification of materials, and by an account of tensile and compressive tests. The Paper is illustrated by fourteen plates, and several wood cuts. M. A. E. Partial Destruction of the Jeetzel Bridge by Flood and its (Zeitschrift für Bauwesen, Berlin, p. 287, 1889.) The bridge in question carries the Wittenberge and Lüneburg railway between the stations of Dannenberg and Hitzacker, over the River Jeetzel, near the junction of the latter with the Elbe. The bridge was constructed for a double line, with three spans of girders on the Schwedler system, each opening being 107 feet 3 inches in the clear, with girders 110 feet 3 inches long, the weight of ironwork in each span being 88 tons, inclusive of flooring and permanent-way. The two piers are 41 feet long, and 7 feet 3 inches broad, each being founded on two semicircular wells of 15 feet 9 inches in length, and 10 feet 2 inches in breadth, sunk to a depth of 13 feet 6 inches, the intervening space being spanned by an arch on which rests the centre portion of the pier. The foundations of the wells were carried down for several feet into a stratum of medium coarse sand, but were not protected in any special manner. The land abutments were laid on the sand and protected from scour by sheet piling. The bridge, erected in 1872-73, withstood the effects of heavy floods until the spring of 1888, when, owing to an ice-dam being formed in the Elbe above the junction of the Jeetzel, the flood burst the banks of the former river at several places near Dannenberg, and flooding the low-lying intermediate district passed into the Jeetzel, and as the railway embankment remained intact, the whole volume of water finding its way again to the Elbe, had necessarily to pass entirely by the bridge-way in question. The scour caused by these abnormal conditions led to a subsidence of the pier nearest Hitzacker, the foundation wells sinking alternately, namely, first that at the up-stream end of pier, then the down-stream, then again the up-stream, and lastly, that at the down-stream end. The total settlement amounted, at the downstream end, to 10 feet 6 inches, and at the up-stream end, to 9 feet 10 inches. In addition to this subsidence, the pier was turned on its axis, so that the down-stream end was brought 10 inches nearer the Dannenberg bank; also the pier was tilted out of the perpendicular across and down-streamwards, to the extent of 1 inch and 5 inches respectively, in a height of 22 feet. The other pier and the abutments, although subjected to great scour, were not affected in level. Diagrams are given, showing the bridge, &c., and a cross-section of the river-bed before and after the flood, also a view of the bridge with the sunken pier. As regards the ironwork but little damage was caused beyond the displacement of the hinged bedplates. On investigation by borings of the river-bed as deepened, it was found that the stratum was of sufficient density to support the extra weight of masonry required in heightening the pier to its former level; also it was found, on examination by an experienced diver, that the pier, wells, and arch were in no way dislocated, and consequently could be used as a base for the new work, the first procedure being to surround the base with ballast to a height of 10 feet above the stream bed, and forming at the top a bench of 6 feet 6 inches in breadth. A detailed description is given of the method adopted of gradually raising in successive stages the girders and flooring, by means of hydraulic (glycerine) jacks of 20 tons lift, the masonry being carried up simultaneously. Four jacks, each worked by two men, were used in lifting each span to be raised, viz., two to each girder end, being bound to the lower boom of the girder ends by wrought-iron rods of 1 inch in diameter, and resting on half-round oak-sleepers serving as rockers, to allow of the alteration in the direction of the axes of the jacks during each lift of from 14 to 16 inches. For distributing the pressure on the masonry, and at the same time packing up the superstructure during each lift, oak slabs were used. The masonry immediately under the bearings of the jacks was laid in quick-setting cement. The girders of the two spans affected were thus raised alternately, an interval of from twenty to twenty-four hours being allowed between the successive lifts for the setting of the cement. To prevent a forward movement of the girders while being lifted, especially during the early stages of the work, when the inclination was considerable, each superstructure was held in check by chains controlled by four crab-winches anchored on the bank, and also strutted against the lower part of the pier. After the girders had been raised to their intended permanent level, they had to be shifted laterally, the one to the extent of 2 inches, and the other 6 inches, which was effected by sliding them on ways smeared with soft-soap, the necessary longitudinal adjustment being made in a somewhat similar manner by tilting the superstructure at one end by jacking-up until movement ensued; during this process, however, there occurred on one occasion an unexpected lateral lurch, causing a breakage of the jacks. After the superstructures were got into their ultimate positions, all that remained to be done, was to replace a few of the wind-pressure floor-diagonals, and complete the bridge-floor over the piers. The above-described work was completed, and the bridge re-opened for traffic on the 28th of August, 1888, the lifting of the superstructure having been commenced on the previous 23rd of June. The cost of the raising of the superstructure and masonry, including the material and making good the permanent-way, amounted to about £592 10s. D. G. [THE INST. C.E. VOL. XCIX.] 2 E |