Dal River Railway Bridge, 1875 (Sweden)

From 'Girder-Making and the Practice of Bridge-Building in Wrought iron', via archive.org

From 'Girder-Making and the Practice of Bridge-Building in Wrought iron', via archive.org

From 'Girder-Making and the Practice of Bridge-Building in Wrought iron', via archive.org

This entry relates to the iron bridge over the Dal River constructed in 1875 by Skerne Ironworks, Darlington.

Note: Old photographs here and here show Järnvägsbro över Dalälven, at Krylbo, Sweden, and it is stated that the bridge was later converted to a road bridge when a new railway bridge was built on the west side around 1916. However, these clearly show a different bridge to that shown in the drawings here. It is clear that the bridge built in 1875 by Skerne Ironworks is at Domnarvet. See c.1918 photo here. It was replaced by a masonry or concrete arch bridge, probably in the 1920s. Photo here.

Construction

The following information is quoted or condensed from a Paper read by Edward Hutchinson of Skerne Ironworks before a meeting of the Institution of Mechanical Engineers at Birmingham in 1876, reproduced in Hutchinson's book 'Girder-Making and the Practice of Bridge-Building in Wrought iron'

Two spans of 80 ft, with a 208 ft centre span. Granite abutments founded on solid rock. The two piers are founded on granite, and are made of granite blocks to about 15 ft above low water level. Above this they were made of bolted flanged cast iron plates filled with cemented brickwork.

'The girders for the side spans are formed with a double system of bracing, and are 10 feet 6 inches in depth; the top and bottom booms, which are of similar section, are composed of plate and angle iron, the bracing ties and struts are of T iron of varying section.

'These girders do not rest directly upon the piers, but are supported by cross bearers fixed between the main girders of the centre span. The rail bearers are level with the top flanges of these girders, so that the rail level is 3 feet 10 inches below the top of the main girders.

'The main girders, which are fixed 17 feet apart, centre to centre, are also formed of a double system of bracing, and are 19 feet 10 inches in depth, and 2 feet 6 inches in width on the flange, and 214 feet 5 inches length of bearing. The top and bottom booms are built up of plates and angle iron, and have a double web of angle and plate, to which the bracing bars are riveted. The bracing is composed in part of H iron, in part of angles and flats riveted, and part of T or L iron

'The rolled joists, rivet irons, &c. were also subjected to special tests. The whole of the ironwork was, in the first place, put together in the contractors' yard at Darlington, and subjected to various tests. It was then taken down and transported to the site of erection in small pieces. Owing to the character of the stream to be spanned by the bridge, none of the ordinary modes of fixing girders of this size seemed quite feasible. The erection of the side spans, of 80 feet each, presented of course no difficulty ; and, if desired in the case of these spans, staging could easily be erected from the abut- ment of the pier, as shown. Between the piers, however, 208 feet apart, it seemed impossible to get the smallest prop or support of any kind. .....

'.... It was, however, ultimately decided to adopt the following plan: Upon the timber staging already provided, the 80 feet girders were riveted up, with their bottom flanges level with those of the main centre girders, as shown on Plate 33, Fig. 4, and on Plate 34, Fig. 6, being temporarily braced together by means of timber struts and the permanent ties, as shown in Fig. 5, at a distance apart corresponding to that of the main centre girders.

'Four strong ties were then fixed between the top of the end of the main girders, and a point near the centre of the 80 feet girders. These ties are shown shaded in Fig. 6 at a, c, and sections of them in Fig. 7 at a, b, c, d. They are all composed of bars, ultimately forming portions of the permanent structure, such as longitudinal rail-bearers, bracing-struts, &c. Special connections, however, had to be provided, and about twelve tons of material of various sections was used throughout for this pur- pose.

'The bottom boom of the 80 feet girders being of insufficient section to stand the compressive strain to which it would be subjected during the process of erection, the strain had to be distributed by means of the compression struts e, Fig. 6, shown in section at E F in Fig. 7 ; these also being composed of parts of the permanent bridge..

'The ends of the main girders being securely braced and tied to the 80 feet girders, as above described, it became necessary to distribute the counterweight in such a way that no undue strain should come upon any part of the 80 feet girders; and in addition to this it was found necessary to strengthen them a little at the centre, near the point of attachment of ties.

'The diagram, Fig. 4, Plate 33, shows how the counterweight, composed chiefly of rails, was distributed : 47 tons being placed at the extreme ends of girders, 18 tons near the point of attachment of ties, and 28 tons in the girders and ties themselves, making a total of 93 tons.

'The weight of the half main-span, with a fair allowance for tools, &c. was ascertained to be 100 tons ; and the distance of the centre of gravity from bearing point on pier 57.2 feet, as shown in Fig. 4. Care was taken that none of the weight came upon the props that projected a few feet outwards from the piers, as shown in the general elevation, Plate 35.

'All being made secure, the process of projecting out the main centre girders was commenced from both piers simultaneously. Each member of the girder was fixed in position in nearly the same form in which it left the works ; that is, no further riveting was done until each piece was in position.

'As the riveting-up of the main girders proceeded, the cross girders which had been riveted up at the works were fixed, as well as the rail bearers and such parts of the main horizontal bracing as seemed necessary to give stability to the work. But the main flange plates, as adding greatly to the overhanging weight, without giving any additional strength, were not put on until the girder was in other respects complete. The weight of the heaviest piece fixed at one operation did not exceed 25 cwt. No special provision in the form of staging for the workmen was provided, planks temporarily laid across the transverse bearers or rail girders being found sufficient for the purpose ; but it was deemed prudent by the workmen to test the stability of the girder occasionally, by running out a small truckload of material, weighing about five tons, to the end of the girder. In the first instance, portable cranes were used in moving and fixing the various parts; but better progress was found to be made with long-jibbed Scotch derrick-cranes, and the use of the portable cranes was abandoned.

'As the girders during erection rested solidly on the piers, and not upon the rollers, great care had to be exercised in order to fix each half in its correct position as to length. This was done by means of a wire stretched across the river, the operation being repeated several times at various temperatures. When the closing piece came to be fixed in position, it did not fill the space by about an inch; but the following day, under the influence of a bright sun, this gap disappeared, and the closing portions had to be driven into their places.

'The bridge was erected during the winter season, and the cold at times was so severe that operation had to be entirely suspended; the days, too, were very short. From these combined causes the erection occupied a much longer time than it otherwise would have done, namely, about five months. When, the main girders having been completed, the temporary ties were cut away, there was only a slight and hardly appreciable deflection at the centre of the main span. No accident of any kind happened in carrying out the work.

'In conclusion, the writer, whilst not wishing to take any credit to himself as having accomplished any very important work, at the same time desires to recom mend to any who are interested in bridge-building the plan here described for cases where the girders are of considerable length, and staging impracticable.'

In the subsequent discussion: 'Captain Galton [ Douglas Strutt Galton?] considered the present communication a very interesting one, as showing a new way of erecting a bridge ; and it would be very interesting to know what the cost of this method was, so as to com- pare the amount of labour expended, and the extra material required with the cost of erecting by staging, because it was quite clear that in many cases of Indian railways such a mode of construction of a bridge might be found very valuable. As regards the strains, of course the bridge during the construction was in a totally different condition from that which it must be in when it had to bear its load; it was not originally formed, he apprehended, for the purpose of resisting those new strains. He should be glad for more particulars to be given as to the strains to which the girders were subjected when in the process of erecting, and those to which they were subjected after the bridge had been erected. ...'

'Mr. F. J. Bramwell referred to the specimen bridge built by the elder Brunel on the grounds of the Thames Tunnel at Rotherhithe. This specimen consisted of a pier and of the half of an elliptical arch on the one side, and about a quarter of a similar arch on the other. These arches were of considerable span, probably 60 feet; they were constructed without any centering, simply of brick in cement, bonded with hoop iron. From the end of the smaller section of the arch was suspended an immense mass of iron to balance the weight of the half arch on the other side.'

See Also

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