WALNEY BRIDGE

(aka: Jubilee Bridge)

THE island of Walney is about 9 miles long, but no more than a mile wide, and it lies on the west side of Barrow-In-Furness In a direction pointing North-West. It is separated from the mainland by the Walney channel, the sea entering from the North at the mouth of the Duddon and on the South from Morecambe bay. Since Messrs. Vickers, sons and Maxim established their shipbuilding and engineering works at Barrow in 1897, a small town has sprung up on Walney Island called Vickerstown, which now contains a population of some 5,000 people. A steam ferry was the only means of communication, except a ford at low tide, between the Island and the mainland; and it was felt, that in view of the development of Vickerstown, some better connection was needed. After several schemes had been considered, a bill for bridging the channel was introduced to the parliament in 1904, and passed the same year, the principal alteration made by the committee being that the proposed opening span of 100 feet was increased to 120 feet. The contract was let in 1905, and work was commenced in the autumn of that year.

Description of the work:

The bridge consists of eight fixed spans ranging from 117 feet 10 inches to 82 feet 8 inches clear waterway between the piers, and one opening span of 120 feet clear waterway between the timber dolphins. The total length of the bridge is 1,125 feet between the masonry abutments, measured along the centre line; the Walney abutment not being placed square to the bridge owing the angle which the approaches make with the bridge. The fixed spans and opening span are all carried on piers each consisting of two cylinders filled with concrete and connected at the top by a capsill grinder. The opening span is on the scherzer rolling-lift principle, into leavers, and is worked by electricity. The width between the parapets is 50 feet, of which 31 feet and 4 inches is taken up by the roadway leaving 2 footways of 9 feet 4 inches on each side. Two lines of tram-rails are laid on the roadway of 4-foot gauge and 10 feet 6 inches between the centres of lines. The scherzer rolling-lift system requires some explanation, as it’s introduction into this country is of comparatively recent date, and up to the present only 4 bridges have been completed embodying this design, although more than one hundred have been built in America and other countries. The first of these bridges to be built in this country was that over the swale, for the southeastern and the Shatham railway company, of 60 feet clear span. The second is in Ireland and was built over the river Suir, near Waterford, for the fish guard and the Rosslere railways and Harbour Company, and is of 50 feet clear span. The third is at Walney and the forth is at Barrow in Furness over the new 100-foot passage between the Ramsden and Buccleuch docks. The motion of one of these bridges when opening is similar to that of a rocking chair, as it rolls back at the same time as the end rises. This rolling motion, besides reducing the fraction, which is met within the case of an ordinary central-shaft bascule bridge, allows the same width of the opening to be obtained with a similar angle of rotation. The angle through which it is necessary to turn the bridge varies between about 70 degrees and 80 degrees, depending on the radius of the rolling segment, in place of an angle of 90 degrees in the case of the ordinary bascule. It has the further advantage that the centre of gravity of the balance weight can be so arranged that the leaf is balanced at an angle of 35 degrees or 40 degrees, so that when opening there is an upward force assisting the motors and a retarding one as the leaf passes the midway position. In closing, the reverse takes place; and this assists materially in reducing the power, and shortening the time required to open and closer compared with the ordinary type of bascule.

With the exception of the Walney bridge, all the above mentioned bridges are single-leafed and embody the earlier designs of the scherzer bridge company, which includes what are known as the operating struts, move backwards and forwards by means of a pinion engaging with the rack of the underside of the strut. The pinions are machinery and operating them are placed on the adjacent fixed span of the abutment, as the case maybe, so as to be clear of the bridge opened the operating struts maybe likened to a pair of shafts connected with the centre of rotation of the rocking chair, which, on being pulled backward or pushed forward, cause the chair to rise or fall. In the case of the Walney Bridge no operating strut is required; what corresponds to it is the stationary rack attached to the pier and gearing with a rotating pinion placed at the centre of the rolling segment. The machinery for actuating the pinion is placed, not on the fixed span as formerly, but is attached to the underside of the opening span, the electric power being supplied by a flexible cable. In this way very much less room is taken up by the machinery, the only part that is seen being the pinions and racks; the weight of the motors and gearing also assist in balancing the leaf.

Foundations From several borings taken along the site of the bridge it was apparent that the foundations would rest in stiff clay as regards the majority of piers, and in gravel towards the Walney side. The clay slopes away towards Walney, being found about the level of ordnance datum at pier No.1, numbering from the Barrow side, some 23 feet below ordnance datum at pier No.4, about 38 feet below pier No. 7, and 50 feet below at pier No.10. The ordnance datum line is the mean between high and low water level, and the tide rises and falls some 14 feet above and below it at spring ties.

Piers:

The cylinders for the piers are of four sizes, viz., 8,9,10 and 12 feet in diameter at the top, enlarging to 12,13,14 and 18 feet 6 inches in diameter at the bottom. The first three sized cylinders carry the fixed spans, and the last sized cylinder the opening span. As all these cylinders are of the same type it will be sufficient to describe one of them, i.e., the cylinder 10 feet in diameter, which was used for six piers. This cylinder is constructed of steel for the lower portion of 18 feet and of cast iron above. The steel portion is divided into 3 parts; at the bottom there is a cylindrical portion 14 feet in diameter and 8 feet high composed of steel plates half inch thick overlapping one another. Three rings of angle iron stiffen the lower 4 feet, and there is a shelf plate 12 inches by 3/8 inch at a height 4 feet from the bottom. The cutting edge plate is 9 inches by 5/8 inch. Above this cylindrical portion there is a truncated cone 8 feet high which reduces he diameter to 10 feet 3 inches, and above this there is 2 feet of cylinder 10 feet 3 inches in diameter, making a total height of 18 feet steelwork. The bottom flange of the cast-iron cylinder is bolted to the top flange of an angle-bar ring riveted on the inside of the steel cylinder a little below the top of the steel shell-plate: the plate stands above the angle-bar ring and allows space for a ¾ inch rust-joint between the inner face of the shell-plate and the outer face of the cast-iron, and thus makes an efficient connection between the steel and cast-iron. At the top of the steelwork there is a diaphragm-plate to which is bolted the airshaft 3 feet 6 inches in diameter; thus all the air-pressure comes on the steelwork and none on the cast-iron rings. A cast-iron cap is placed on top of the cylinders, and about two feet below it there is a moulding cap on the cylinder. The height of the cast-iron rings is 5 feet, with the exception of the closing lengths, which of course varied. All the rings up to and including those 10 feet in diameter were cast in one piece, but the 12-feet rings were in four segments bolted together. The thickness of the metal is 1 ½ inch for the 12-foot rings and 1 ¼ inch for the others. Where the tide allowed it the cylinders were pitched into position on the ground and built up there; but where the water was deep, they were built up on a staging and lowered by means of three hydraulic jacks with hollow rams through which the lowering links passed. These links were formed of flat steal bars, alternately double and single, and were connected at the bottom with brackets riveted to the sides of the cylinder. There were slots in the links corresponding to the travel of the ram. Before the excavation, the cylinders were partly filled with a ring of concrete starting from the shelf plate and continuing up to the diaphragm plate, leaving a working-chamber the full diameter of the cylinder for 4 feet up and after a conical air space. The excavation was, as far as possible, commenced in the open; but compressed air had to be used before much progress could be made. The clay, which was the principal material excavated, was in all cases fairly tough, and in places interspersed with boulders, the rate of excavation for this material being about 40 skip-loads per working shift of 9 hours and the same by night. The maximum number of loads got out in 1 shift 130 of fine sand, about 3 loads to the yard, at pier No. 10. The cylinders were sunk until either hard boulder clay or ballast was reached, and varied but little from the depth shown on the contract drawings, with the exception of the pier nearest the Walney abutment. The greatest depth at which any cylinder was founded was 30 feet below the bed of the channel, or nearly 62 feet below high water of spring tides. The maximum air-pressure used was about 27 lbs. Per square inch, but no trouble was experienced with the men, only one case of “bends” being recorded, the man having had them before in compressed-air work and being to old to continue work of that nature. The depth to which the cylinders were sunk was determined by sinking until a satisfactory foundation was obtained and the top of the steel-work was about 10 feet below the bed of the channel; when this depth was reached, the cylinder was filled with 4-to-1 concrete for a depth of 4 feet from the bottom, and then with 6-to-1 concrete to just below the diaphragm plate. All this was done under compressed air, and the pressure was maintained for about 24 hours, when it was allowed. The airshaft was then unbolted and removed, and the cylinder was filled with 6-to-1 concrete in the open. No weights were used to force the cylinders down; but the concrete was put in round the airshaft to add to the weight. As the estimated load on the foundations was a maximum of about 5 ¼ tons per square foot, a test load of 25 per cent. More, or 6 ½ tons per square foot, was used in order to ensure that there should be no settlement during the erection of the superstructure or afterwards. The load used consisted of rails, these being laid on girders, which in turn were bedded on 12-inch timbers fitted inside the cast iron rings and resting on a level bed of ballast. The height of the timbers and ballast was so arranged that the girders could be wedged up from under the top of the cast-iron, thus throwing some weight on the cylindrical rings. This, however, was not done until a considerable weight had come direct on the concrete. The greatest load applied to any one cylinder was 1,360 tons, or 6 ½ tons per square foot, and the maximum settlement was about ½ inch; in many cases no settlement at all could be detected. The full test load remained on for at least seven days. The cylinders are connected together at the top by a heavy capsill girder embedded in the concrete, which is at this point composed of 4-to-1 concrete, this proportion continuing 3 feet below the capsill girder to act in place of a stone bearing-block. The capsill girders have two webs 1 inch thick, which are 3 feet 6 inches apart and 3 feet deep. The webs are stiffened with angles and diaphragms under the bearings, the whole being filled up with solid with concrete well rammed into all of the corners. The top plate of the capsill girder is 1 or 2 inches above the cap of the cylinder, which allows the top to be sloped outwards the whole being coated with 1 inch of asphalt and rendered waterproof. Four holding-down bolts are used, 12 feet long by 1 ½ inch in diameter. The making-up lengths for the cylinders were inserted just above low-water level, and so cast that they brought the upper portion of the cylinder to the correct position if it was only slightly out, or half-way to it in the worst cases, the remainder of the adjustment being made in the capsill and the girders and bearings.

Abutments:

The Barrow abutment carries the toll-houses about 87 feet in length and the concrete foundation, which is carried on creosoted pitch pine piles 12 inches square, the piles being spaced 3 feet to 3 feet 6 inches between centres where they carry the bridge proper, and about 4 feet between centres between the toll-houses. The foundation was on hard clay and the piles were driven until the last six blows from a 25-cwt. hammer falling 6 feet did not cause a greater settlement than 1 ¼ inch. The average length of the piles was 15 feet, and they were cut off a foot above the foundation, which was formed as a 6-to-1 concrete 6 feet thick. It was anticipated that the Walney abutment would cause more trouble than that at Barrow, as the adjacent pair of cylinders had to be sunk 10 feet lower than the contract drawings allowed for before a satisfactory foundation was reached; and the result of the preliminary excavation bore this out. At the proposed level for founding the abutment, in place of gravel a sort of running sand was encountered, being a mixture of sand and clayey material. A series of seven boreholes showed this to exist in varying thickness over the whole area, but at some feet below it there was a bed of fairly coarse gravel. It was therefore decided to found the abutment on this gravel and extend and strengthen that part of the foundation under the main girders. To do this effectually it was necessary to drive a watertight dam. This was composed of timbers 12 inches by 6 inches, bolted and dogged together in sets of three, with felt between the joints, the outside timbers being cut with a ‘V’. The piles were 32 feet long, and, allowing for the joint, 2 feet 9 inches thick, and they were driven about 20 feet into the ground by means of a wide piling-hammer cast specially to drive the three piles at one time. The dam was of irregular shape to suit the outline of the abutment, but no difficulty was found in making it watertight. Clay was dumped on the outside and rammed against the timber, and the joints were caulked with oakum. No king-piles were used, but three sets of wailings, 12 inches by 6 inches, were fastened on both sides with the usual system of struts. Chains acting as ties also helped to make the dam rigid and to prevent any movement due to the flow of the high tides. The top of the dam was about 2 feet above the high water of spring tides, at which time the head of the water above the lowest foundation was about 20 feet. Two sluices were put in as low as possible, and a pulsometer-pump 3 ¼ inches in diameter sufficed to keep the water down. The original surface o the ground was about 7 ½ feet above ordnance datum, and when the excavation had passed through the strata of clayey sand and reached the bed of gravel, at a depth of 4 ½ feet below ordnance datum, it was found that at high tide the water came up through the ground and formed a number of small blow-holes. The bearing piles, which were driven 3 feet to 3 feet 6 inches apart between centres, stopped this to some extent; but it was considered advisable before putting in the concrete to spread a layer of cement bags over the foundation to prevent the water bubbling up and disturbing the concrete. The excavation was taken out in three sections, that is to say, the dam was not divided up in any way but one part of the foundation was always in advance of the next part, steps being left in the concrete to make a bond. One of the principal reasons for spreading the foundation lay in the fact that no satisfactory test could be obtained from pile driving. Two test piles were driven, the longer one being 43 feet in length. At a point about 21 feet into the ground it sunk 1 ½ inch for six blows of a 25-cwt. hammer falling six feet; but this set gradually increased and then diminished slightly, till when the pile was 43 feet into the ground it sunk 2 7/8 inches for the same test. The borings indicated that there was a bed of coarse gravel at the point where the test pile went 1 ½ inch for six blows; so that it was decided to stop the bearing piles in this gravel. These piles were, therefore, about 14 feet long, and were allowed to project, as in the other abutment, 1 foot into the concrete. For the last six blows they went from 3 inches to 4 inches. Taking the worst condition of loading, and assuming that no load is taken by the ground. For that part of the wall under the bearings the load per pile is about 16 tons, this being the mean, as the centre of pressure is very close to the centre of gravity of the wall at this point. The wall under the bearings is 21 feet wide, and projects beyond the line of the proper wall some 6 feet. The whole of this portion is strengthened by the insertion of 15 inches by 6 inches rolled steel joists, 20 feet long, placed transversely to the wall, with 6-inch joists in three alternate layers above. The concrete for the first foot in the foundation of the main wall was put in 4-to-1, and for the rest of the foundation 6-to-1. Where the sump had been, and at any part, which it was difficult to drain thoroughly, 4-to-1 concrete was put in bags and well rammed in. To strengthen the foundation further, it was decided to cut the sheeting piles off at ground level, and carry the concrete hard up against them. The foundations for the wing-walls call for a little comment. The dams used here were made of two half timbers dogged together, making one pile 2 feet by 6 inches, with plain joints which proved tight enough, as the foundation-level was about 8 feet higher than in the main wall. Bearing piles were used but were spaced further apart, and the sheeting piles were also left in. Weep-holes are provided in the main wall but not in the wing-walls, as all the water drains towards the main wall. The back of the Walney abutment is covered with one thickness of Callender’s sheeting, the bottom being fastened down with rammed clay, sloping from the wing-walls downwards to the main wall so as to drain the water towards the main-wall. The Barrow abutment, in place of the sheeting, was plastered with 1-inch 2-to-1-cement mortar. Both abutments had one foot of rubble backing behind them. The stone used in facing the abutments came from the neighbouring quarry of Newton, and is very good white limestone. The facing starts about 18 inches below the level of the ground, and is rock faced, with beds and joints dressed, up to the level of the steelwork. The tollhouses and pilasters are hammer-dressed, and the stringcourses chisel-dressed. Barrow abutment carries the tollhouses, which are built of stone with a slate roof. The basement is used as a lavatory on one side, and as a storehouse on the other. The upper floor id fitted up as an office with a fireplace, electric light, telephone to the operating cabin, etc. A pair of gates across the roadway, and side gates across the footways, is placed between the tollhouses to control the traffic.

Superstructure:

The superstructure is composed of two main girders of the ‘N’ type, with cross girders and a longitudinal floor beams carrying jack arches of concrete. The level of Walney approach-road being 6 feet lower than the Barrow approach it was not possible to make the girders all of one depth, as a headroom of 6 feet above the high water mark of spring tides had to be kept. Consequently the main girders are one of three different depths; but the distance, 11 feet and 6 inches, between the posts is kept uniform to simplify the floor. There are five spans having eleven bays, each 11 feet and 6 inches long, with main girders 14 feet deep over angles, one span with ten bays and main girders 12 feet and 6 inches deep, and two spans with eight bays and main girders 10 feet deep. These girders do not call for any special mention; the booms are 17 inches deep the lower booms being open, with angles 4 ½ inches by 4 ½ inches by 5/8 inch and webs ¾ inch thick. The main girders are 31 feet apart between centres, and on cast-iron fixed bearings at one end and on rolled-steel rockers at the other. The rockers are turned to 8 inches in diameter and they are 4 inches wide; the Weight on them per lineal inch, with maximum loading possible, is about 26 cwt. The cross girders are 3 feet deep, and come just under the bottom angle of the top boom, so that the top of the longitudinal girders, which are 15 inches deep and of built-up section, is some 3 inches below the top of the main girders. At the ends of the main girders, the cross girders are raised so as to be jest below the level of the top angles of the main girders, and an expansion plate connects the ends of the two adjacent spans, being riveted to the end girder of the fixed span and free to slide over the adjacent girder. The longitudinal floor-beams are seven in number and spaced to suit the tramlines. The thickness of the concrete at the crown of the jack arches is 8 inches; and before any concrete was put on the shuttering the latter was coated with an inch of cement rendering, and on this 4-inch prismatic creosoted oak blocks were laid. Expansion joints were placed in the oak blocks every 40 feet, and they were made of one thickness of patent compressible packing. An inch expansion joint was also left in the concrete over the piers and the space filled with bitumen. Two conduits were made in the concrete for electrical cables, one along the centre for the arc-lamps, and the other and larger one on the North-side, for general supply purposes, etc. Cast-iron gullies are let into the concrete for drainage, and bolted to the main girders. The curbs are of granite and the joint between them and the roadway was made with puddled clay. The footways are carried on brackets, these supporting a longitudinal channel bar, on the top of which are small rolled steel joists, 3 inches square. The area is thus divided into spaces about 2 feet 6 inches by 3 feet 8 inches, which are filled with 6-to-1 concrete reinforced with expanded metal. A layer of cement mortar was first put on the shuttering, and then the expanded metal was bedded in it, and the concrete, which is three inches thick, shovelled on. The surface is made of two inches of tar-macadam. This, as well as the wood paving and granite curbs, was laid by corporation. The parapets are of the closed type 4 feet 6 inches in height, made of steel plates with inside cast-iron skirting and outside cornices. A moulding runs along the top, and the joint at each bracket is covered by a small pilaster and panel on the inside, a larger pilaster and panel being used over the piers, where expansion is provided for. The parapet between each bracket is divided into three half-round vertical bars on the inside and small channels on the outside. Cross bracing is introduced between the main girders over the piers, and at intervals between them. It consists of a bottom member attached to the lower boom of the main girders, with bracing members joining the cross girders. Cast-iron screens are placed around the bearings to shelter them, and to hide in some measure the difference in height of the main girders.

Opening span:

The opening span is carried when closed by two pairs of cylinders 12 feet in diameter at the top, opening out to 18 feet 6 inches at the bottom. A longitudinal capsill girder passes from these back to the adjacent cylinders 25 feet away from carrying the fixed spans. This girder is 33 feet 9 inches long and 5 feet 6 inches deep, and it carries the track girders along with the bascules roll. As the capsill girders would be immersed in the water, at high tides, for the greater part of their height, they are surrounded by box girders to within 1 foot of the top and filled with concrete and waterproofed. The track girder is 16 feet and 11 inches long and 6 feet deep. It has a single web of two ½ inch plates, and the top flange is composed of 8 inch by 6 inch by ¾ inch angles and a series of 6 plates 14 inches, 21 inches and 27 ½ inches deep by ¾ inch thick. The top is planed to give bearing to the track plates, which are malleable steel 2 inches thick, the double row of teeth or studs projecting a further 1 7/8 inch. The total length of roll is 14 feet 10 inches. The track girders are braced together by two girders 6 feet deep, with lattice webs, and cross-bracing top and bottom. There are two main girders for each bascule, composed of a single web with 8 inch by ¾ inch angles and flange plates 20 inches wide top and bottom. The depth of the girders ranges from 5 feet at the centre to 15 feet 3 inches over the centre of rotation. The web and flanges are greatly strengthened at this point by a series of side plates and stiffeners. The radius of the 20 inch by 2 inch curved plate riveted to the rolling segment is 11 feet 6 inches; and it is machined on both sides, so as to fit close to the rolling segment, which was also machined to receive it. Recesses are slotted through the plate 1 foot and 7 inches apart “staggered” for the studs on the track girder. The rear or tail end of the girder is 6 feet and 2 inches deep, and has at the end a bearing plate, which comes in contact with the underside of the bumper block seating on the fixed span when the bridge is closed. There is also a seating or bearing against which the pawls of the rear lock act so as to prevent any deflection of the rear end under passing loads. The anchorage for the opening span is taken by the adjacent fixed span down the inclined end ties to the foundation bolts. The weight of the fixed span is sufficient to counterbalance the upward pull brought on it by loading the opening span with the assumed full live load, but provision is also made for double this amount by three foundation bolts, 3 inches in diameter, in each cylinder. The bolts are of high tensile steel, each 30 feet long, the anchor plate at their base being a circular casting 4 feet in diameter. At the top the bolts are securely fastened to the gusset plates, and before the nuts were screwed down the bolts were stressed up to 6 tons per square inch by means of hydraulic jacks. This permanent tension was given in order to prevent any lengthening of the bolts should a pull come on them. At the top of the incline ties are gussets connecting them with the top boom, and between them is placed the steel bumper block in a stirrup formed of a bent plate riveted to the gussets. The tail end of the main girders for the opening span is narrowed so as to pass between these ties with 2 or 3 inches of clearance on each side. The arrangements for locking the opening span at the centre are simple and effective. On the Barrow leaf are formed, at the end of them main girders, two projections, an upper and lower one, from the extension of the web and top and bottom angles. The lower projection is longer than the top one, and they form, as it were, a pair of jaws with the lower protruding. The Walney girders, on the other hand, are cut square with the lower side bevelled off. Instead of the single web continuing to the end, double webs are formed beyond the last cross girder, that is to say, for a distance of some 3 feet 5 inches, and across the end of those webs is placed a cast-steel diaphragm projecting in the form of a nose. As the leaves are closing, the Barrow one stops automatically at a certain point when nearly closed, until the Walney nose end has entered the jaws of the Barrow leaf, when they close together. The nose of the Walney leaf slides along the upper surface of the lower jaw of the Barrow leaf, and at the same time this lower jaw passes between the two webs of the Walney leaf. There is only a slight clearance between the upper surface of the nose and the lower surface of the top jaw of the Barrow leaf, so that the two leaves are locked in all directions. One leaf cannot deflect without the other; and there is a total absence of hammering at the centre under the passage of a heavy load, the rolling action of the leaves giving sufficient forward movement to allow the Walney end to bolt itself into the jaws of the Barrow end. The cross girders are placed 15 feet apart, with the footway brackets 7 feet and 6 inches apart. The cross girders are hog-backed to suit the camber of the roadway, and increase in depth as the main girders deepen. The floor for the roadway is composed of steel joists 15 inches deep with steel floor-plates 3/8 inch thick laid on the top. The latter are coated with two thickness of pure bitumen brushed on while hot and dusted with cement. On the top of this, where the tram rails were laid, tarred felt was placed; but the remainder of the roadway was laid with creosoted pitch-pine planks, covered with 2 inches of diagonal karri wood planking 4 inches wide. The joints between the pitch pine planks were run with bitumen, and also the boltholes and the space between the planks and the rails. On either side of the centre of the rolling segment are two special cross girders 10 feet deep, between which the machinery is placed. From the rear cross girder, which is 9 feet from the centre of the segment, longitudinal girders are cantilevered out dividing the roadway into five boxes open at the bottom, into which the counterweight is put. The last cross girder is thus some 10 feet and 6 inches from the end of the span, so as to allow the counterbalance chamber to pass between the capsill girders when the bridge is opening. At the same time, the rear ends of the main girders pass between the webs of the capsill girders, clearance being left in the concrete with which the latter is filled. An oak bumper block is placed against the end of the track girder on each side, and bolted to the top of the capsill girder to act as a stop; but the leaves are always brought t rest before reaching the block. The travel of the leaves when opening makes it necessary to cantilever out the adjacent fixed spans in order to give clearance to the balance weight. In the present case the roadway was cantilevered out from the last cross girder, some 9 feet and 6 inches back, and was supported on brackets. The space between the ends of the fixed and opening spans and the centre of the latter was covered over by grooved steel plates fastened to the fixed spans in the former case, and to the Walney leaf in the latter case. The footway is carried by longitudinal channel-bars; to which are bolted 6-inch by 3-inch pitch-pine runners, and over these 3-inch creosoted pitch-pine planking is laid. The hand railing is made of gas piping standards and rails, with vertical bars. As the hand railing approaches the fixed spans it is widened out so as to pass outside the fixed span when the bridge is opening the last bay of the fixed span parapet being also made of gas piping to facilitate this.

Operating gear, etc:

The opening span is operated entirely from the Walney cabin, as the electric power is brought to the bridge by a main on the Walney side. There is also an emergency hand-gear which is placed on the dolphins and geared to two speeds, so at to enable two or four men to work. The power from the winch is taken by a horizontal shaft through the track girder, and is transmitted to the first motion shaft by means of mitred wheels and a pendant shaft which slides up and down through a square sleeve in the lower mitre-wheel, during the opening and closing of the leaf, while the top driving mitre-wheels on the shaft follow the horizontal travel of the centre of rotation. The hand gear is only for emergency purposes, and is brought into use by means of an ordinary clutch. For the purposes of opening and closing, two 25-break horsepower motors are used in each leaf. They are of the ironclad multipolar type and are placed, together with the gearing, under the roadway of the opening span. They are geared to the same shaft, and transmit motion through cast-steel gearing to the pinions engaging with the racks outside the main girders on each side of the bridge. No weight is taken by these racks, as the whole weight of the opening span is on the track girders. The rotation of the pinion along the rack causes the leaves to open and close in the same way, as rotating the hub of a wheel would cause it to move backwards and forwards. A powerful magnetic brake of the twin solenoid type is fitted to each leaf, the drum of the brake being keyed to the first motion shaft. An emergency oil-brake is fitted to the Walney leaf, and a magnetic break to the Barrow leaf. The gearing and motors are fixed to the girder work of the opening span and turn through an angle of about 74 degrees; the power being brought to them by a cable encased in flexible piping. At the rear end of the opening leaves and attached to the fixed span there is, as previously mentioned, an eccentric locking pawl which bears against the seating provided at the end of the main girders of the opening span, and so prevents any deflection of the back end of the leaf under passing loads. The pawl is actuated through worm gearing by a shaft driven by a 2 brake horsepower ironclad and the gear there is a magnetic clutch to obviate the danger of the former being damaged by excess of current. The cabin on each side of the opening span is cantilevered out on brackets beyond the footways. That at Walney has a floor space of 22 feet 6 inches by 11 feet 8 inches and is painted inside with fireproof paint. When opening or closing the bridge, the operator stands facing the Barrow side, and before him is placed a set of eight levers, with room for a spare one, similar in type to those in the signal cabin of a railway. Before starting, all the levers are in the normal position, the bridge circuit is open and the magnetic brakes are on. When No. 1 lever is pulled over, the tramway circuit is opened, No. 2 lever closes the bridge circuit Nos. 3 and 4 levers unlock the rear ends of the leaves, Nos. 5 and 6 levers raise the two leaves, and Nos. 7 and 8 levers lower the respective navigation signals for up and down channel traffic. All these levers are mechanically interlocked on messers. Steven’s system; and, as an additional safe guard the levers for opening and closing the bridge are automatically controlled. The operation of opening may be recapitulated as follows: When a vessel approaches she has to make a signal if she wishes to pass through. The operator then cuts off the electricity supply to the tramcars, and stops the road traffic by placing light chains across the bridge. He then opens the bridge and signals to the vessel that the passage is now clear. When closing the bridge the reverse process is gone through. The bridge can be held in any position by the magnetic brakes against any wind pressure in which vessels could navigate the channel. When the current is off the bridge, the brakes are put on by a powerful steel spiral spring, and they are taken off by the twin magnets, which are designed to exert a pull off 400 lbs. Each. The method of controlling the levers for opening and closing the bridge is as follows: An endless chain is taken on pulleys, from the centre of the operating pinions, through the floor of the cabin and passed round a drum with spiral grooving, so that the travel of the pinion along the rack causes the drum to revolve backwards and forwards as the bridge is opened and closed. Two cam drums are geared to the chain drum, and are fitted with cams so arranged that at the critical positions of opening and closing they engage with the friction rollers mounted on standards, forming the uprights of a sliding carriage, which move in and out and so regulate the controller levers through the connecting rods under the floor of the cabin. The chain drum also actuates a pointer, which is fixed to a large dial and shows the exact position of the Walney leaf when opening and closing. A similar arrangement if indicating gear is placed in the Barrow cabin, the chain drum in this case operating switches, so that the opening or closing positions of the Barrow leaf are shown by means of six electric lights placed to indicate the same on a dial in the Walney cabin. One of these positions is when the Barrow leaf is nearly closed, as it has to be started a few seconds before the Walney leaf so as to wait for it when nearly closed, until the Walney nose end bears on the projecting jaw of the Barrow leaf, when they both go down together. The cams are set on the drum so as to control this operation, and to ensure that in all operations of opening and closing the power is put on and cut off at the right moment. By means of the interlocking and automatic controlling gear, it is only necessary for one man to be employed in the cabin to carry out all operations of signalling, opening, or closing the bridge. Both cabins are fitted with electric light, telephones, etc., the telephone in Walney cabin being connected with the telephone exchange. The electric power is supplied from the mains of the barrow corporation, and taken to the barrow cabin through submarine armoured cables laid in a trench, some 4 feet deep, across the bed of the channel. The signal masts are of steel lattice work and are placed at the side of the cabins, accesses to them being obtained by a ladder leading over the parapet on to a platform, on which is placed the motor for running the marine ball up and down the mast. An emergency hand-winch is also provided for this purpose. The starting and stopping of the motor is automatically controlled from the Walney cabin. The marine ball is painted green; and at night, lights with green and red spectacles are used. Tram-rails have been laid the whole length of the bridge, connecting the approaches. On the opening span there are two standards to each leaf, and the slack of the wire when the bridge is opening is taken up in special trolley poles provided on the fixed spans. Each pole is designed to take up to about 63 feet of wire. As the bridge opens the wire is coiled round drums provided for the purpose, which are actuated by falling weights. All the parts are very carefully insulated, bands of ambroin being used for this purpose.

Dolphins:

The lengths of the dolphins were settled by Sir William Matthews, K.C.M.G., Passed President Inst. C.E., at arbitration between the corporation of Barrow-In-Furness and the Furness railway company. They are 300 feet long, 150 feet being on the South side, and 100 feet on the North side, the remaining 50 feet surrounding the piers. The radius at the nose is 12 feet, and the dolphins widen out to 29 feet 6 inches under the bridge. They are composed entirely of Karri wood, 250 piles 14 inches square being used. These piles are over 50 feet in length, and are driven some 20 feet below low water level of ordinary spring ties. There are the usual raking piles to give stability. Underneath the bridge, where the counterweight comes, the dolphin is cut away so as to afford clearance when the bridge is open. This part of the Dolphin was therefore specially strengthened with raking piles and struts. The piles were driven by a 30 cwt. hammer, falling 3 feet; as it was found that there is less liability to split the pile if a heavy blow is given with a short drop. The walings are 12 inch by 6-inch timber and are checked into the piles, being secured by 1-inch bolts and straps. The decking is 6 inches thick at the nose end, and 3 inches elsewhere. Five cast-iron bollards are placed on each dolphin, the bollards passing over the top of a pile and being secured to the pile with bolts and straps, the interior being grouted up solid. All wrought iron work is galvanised. Two fair leads are fixed to each dolphin, one at each end; and there are also four electric lights on each dolphin, an arc lamp at each end, and one electric light near the racks. Access to the dolphins is obtained from the cabins down a flight of steps, and a gangway, which passes under the bridge. When the bridge is open there is also a passage from one part of the dolphin to the other in front of the opening leaves. The level of the deck is 21.25 ordinants datum, or 7 feet 3 inches above high water of spring tides.

Erection:

For the purposes of erection a substantial timber staging was built, leaving an opening of 120 feet in the centre of the channel. By act of parliament a clear channel of 100 feet had to be maintained throughout the erection of the bridge: accordingly, the two leaves were built in a rolled back position in their correct alignment. A 10-ton crane on each side with a 65 foot jib was sufficient to carry out the erection of the opening span, nearly all the steelwork being in place, with the exception of the last bay of floor plates, before the leaves were lowered. The last piece of steelwork on the end of each main girder was not riveted up until the leaves were lowered, but it was found that very little adjustment was necessary as ½ inch covered the error in any direction. The fixed spans were built up in place, and riveted with hydraulic riveters where possible, otherwise pneumatic riveting was adopted. The air-pressure used in these was maintained at 100 lbs. Per square inch. After the steel work was assembled at the contractors yard it received a coat of red lead, and, after erection at the sight, one coat of red lead and two coats of dark red oxide paint; the panels of the parapet being picked out with French grey. All the iron castings were dipped in Dr. Angus Smith’s patent solution, and were afterwards painted with two coats of viaduct; the capsill girders and underside of the floor being also coated with this solution. The total weight of steel in the superstructure amounts to 2,150 tons, of which about 365 tons was used in the opening span. In addition to this, 250 tons of steel was put into the piers and 675 tons of cast iron; and 500 tons of cast iron was used in the parapet and as counterweight. The total cost of the work including roadway and tramway lines, etc., was over £115,000. The bridge was commenced in the autumn of 1905, and was opened on the 30th July 1908, by the mayoress of Barrow, but was not completed until the autumn of that same year. In September 1908, trials were taken to ascertain the power used and the time taken to open the bridge. In the first instance three trials were taken of the two leaves opening and closing together, from the time the rear ends were unlocked. The mean of these trials was as follows: The leaves opened in 77 seconds, using 0.5754 Board Trade unit, at an average of 35.8 electric hoarse-power. The leaves closed in 96 seconds, using 0.5985 Board of Trade units, at an average of 28.0 electric horsepower. The total for both operations took 173 seconds, and used 1.1739 Board of Trade unit. A further three trials were taken, starting from the unlocking of the leaves by the rear lock motors. In this case the mean result was as follows: The leaves unlocked and opened in 96 seconds, using 0.66 Board of Trade unit, at an average of 33.0 electric horse power. The leaves closed and locked in 127 seconds, using 0.83 Board of Trade unit, at an average of 31.6 electric horsepower. The total for both operations took 223 seconds, and used 1.49 Board of Trade unit. The engineers for the bridge were the late Sir Benjamin Baker, K.C.B., K.C.M.G., Past President Inst. C.E., and Mr. A.C. Hurtzig, M. Inst. C.E., the work being designed and erected under the supervision of their bridge engineer, Mr. E. M. Wood, under whom the Author worked first on the design, and afterwards as Resident Engineer on the bridge. The contractors were Messrs. Sir William Arrol and Company, Ltd., who were represented at the site, for the first part of the time by Mr. H. Cunningham, Assoc. M. Inst. C. E., and for the letter part by Mr. W. Burnside. The sub-contractors for the electrical equipment were Messrs. Crompton and company, Ltd.

 

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