TABLE No. VIII.—CIRCULAR GRANITE PIERS.—TABULAR STATEMENT OF QUANTITIES.
All Excavation—Concrete, Rubble, and Brickwork in Cubic Yards. Granite in Cubic Feet. Steel, Iron, and Cast Iron Tons, Cwts. and Qrs.
| Piers. Q.–Queensferry. |
Excavation | In Foundations below Low Water. | In Circular Pier. | Steel. | Iron. | Cast-Iron Anchor Plates. | ||||||||||||||
| Concrete. | Brickwork. | Rubble. | Rubble. | Granite. | Brick-work. | Cutting Edge of Caisson &c. Plates. | Holding down Bolts. | Caissons. | Bolts. | |||||||||||
| Tons | cwts. | Tons | cwts. | qra. | Tons | cwts. | Tons | cwt. | Tons | cwt. | ||||||||||
| Q.N.E. | Mud and boulder clay. | 6827 | 9801 | Nil | Nil | 2376 | 13,621 | Nil | 52 | 7 | 9 | 6 | 3 | 399 | 0 | 9 | 9 | 12 | 12 | |
| Q.N.W. | 6271 | 7547 | 1105 | " | 2376 | 14,543 | " | 52 | 7 | 9 | 6 | 3 | 399 | 0 | 9 | 9 | 12 | 12 | ||
| Q.S.E. | 6651 | 7361 | Nil | " | 2305 | 13,237 | " | 52 | 7 | 9 | 6 | 3 | 338 | 5 | 9 | 9 | 12 | 12 | ||
| Q.S.W. | 6372 | 7089 | " | " | 2305 | 13,237 | " | 52 | 7 | 9 | 6 | 3 | 340 | 7 | 9 | 9 | 12 | 12 | ||
| G.N.E. | Whinstone rock. | 755 | Nil | " | 236 | 2300 | 13,237 | " | Nil | 9 | 6 | 3 | 24 | 3 | 16 | 14 | 12 | 12 | ||
| G.N.W. | 324 | Nil | " | 608 | 2300 | 13,237 | " | Nil | 9 | 6 | 3 | 38 | 10 | 17 | 1 | 12 | 12 | |||
| G.S.E. | 1054 | 5635 | 626 | Nil | 2300 | 13,327 | " | 95 | 16 | 9 | 6 | 3 | 334 | 13 | 6 | 12 | 12 | |||
| G.S.W. | 831 | 6576 | 626 | Nil | 2300 | 13,237 | " | 95 | 16 | 9 | 6 | 3 | 360 | 11 | 13 | 6 | 12 | 12 | ||
| F.N.E. | Whinstone rock. | 438 | Nil | Nil | 264 | 854 | 6484 | " | Nil | 8 | 12 | 2 | Nil | 8 | 12 | 12 | 12 | |||
| F.N.W. | 444 | " | " | 481 | 494 | 6842 | 350 | " | 8 | 12 | 2 | " | 8 | 14 | 12 | 12 | ||||
| F.S.E. | 1004 | " | " | 836 | 2300 | 13,237 | Nil | " | 9 | 6 | 3 | 48 | 2 | 20 | 9 | 12 | 12 | |||
| F.S.W. | 823 | " | " | 200 | 2300 | 13,237 | " | " | 9 | 6 | 3 | 21 | 17 | 16 | 13 | 12 | 12 | |||
The latter two courses are of Cornish granite, the others of Aberdeen granite, both light grey in colour. The blocks of rock-faced granite have the edges dressed to the batter of the pier, and to horizontal and vertical joints. The courses are alternately headers and stretchers, with a bond of not less than 9 in. The joints are not more than 1⁄4 in. wide, and are pointed from the outside with pure cement.
The hearting is principally of flat bedded Arbroath rubble, but a large number of whinstone blocks roughly squared were also built in. In building the pier the rubble masonry closely followed the setting of the granite, and both vertical and horizontal bond was strictly observed. Between the concrete in the foundation and the rubble masonry in the piers bond was also established by large blocks of whinstone squared to obtain proper bedding. (See Figs. 54 and 55.) At this point a wrought-iron belt 56 ft. in. in diameter, 18 in. in depth and 3⁄4 in. thick, made in sections and rivetted together, was placed and built in. A second belt of similar strength, but only 43 ft. in diameter, was built in about 2 ft. below high water, and a third belt of double strength, or 11⁄2 in. thick and 39 ft. in diameter, was built in just behind the coping course. All these are shown in Fig. 54.
When the level 7 ft. below high water was reached a temporary timber stage was erected and carried to the level of the underside of the fixed bedplate about 17 ft. 6 in. above high water. Upon this a templet of the bedplates made of light angles and 1⁄4-in. plate in four sections bolted together, which had all the holes for the holding-down bolts in it, was laid, correctly centred and screwed down. The bolts with anchor plates supported by nuts were then carefully set up and built into the rubble masonry, a space of a few inches being left round each bolt to admit of subsequent adjustment. This is very distinctly seen in Plate VII.—Inchgarvie north-east pier. The building of the pier was now continued, the position of templet and holding-down bolts being frequently checked to insure correctness.
From the plan it will be seen that the coping course consists of alternate headers and stretchers.
The top or crown of the pier is slightly spherical, and is built up of blocks of dressed Aberdeen granite from 17 in. to 18 in. in thickness. The blocks fitting into and adjoining the coping course were all cut to wooden templets sent, the remainder being arranged in straight courses. The blocks project from 6 in. to 12 in. under the bedplate, a recess being cut out to receive the latter. The remaining space under the bedplate is made up with Arbroath rubble masonry, and in one case with a tolerably thick layer of Staffordshire blue bricks built in cement.
The mortar used in building the piers was throughout of one part cement and two parts of sand, and was mixed in a pugmill close by. At first hand cranes only were used in the building, but steam cranes were substituted as being more handy and expeditious. Both granite blocks and rubble were handled and set by means of pointed chain-clips, holes being picked for the purpose.
The holding-down bolts in each pier were forty-eight in number, in four rows of twelve each. They are set at 2 ft. 9 in. and 7 ft. respectively to each side of the centre line, and are longitudinally about 3 ft. apart. Owing to the inward set of the bottom members in cantilevers, rather more than half of the bolts are set in a line parallel to the centre line of the bridge, the remainder following the deviation of the bottom member. In order to bring the largest possible mass of masonry into play, the four centre-bolts of each outside row are bent outwards, as shown in Fig. 54, and to prevent any tearing action upon the masonry which would be produced by the bolts being drawn tight at top, cast-iron shoes are inserted at the point of kinking, and these are held together by a pair of angle-bars to each pair of bolts. (Figs. 56, 57, 58, and 59.) The holding-down bolts are of a special steel. They are 21⁄2 in. in diameter, with an enlargement to 3 in. at both ends, where a screw thread is cut upon them. They are about 25 ft. long. The anchor plates are 2 ft. square with a long boss, stiffened by four diagonal ribs, and are held by an ordinary nut. The bolts received several coats of tar before being built in.
When the masonry had been carried to within about 8 ft. of the top the templet had to be removed to allow the rubble to be placed in position, but it was replaced from time to time, and the position of the bolts frequently checked. As the heads of these bolts fitted in the lower bedplate without any play whatever, it was necessary that their position should be absolutely correct.
When the masonry had got up close to the under side of the bedplate the bolts were again set with the greatest care, and the spaces left round them were filled up with cement grout to within about 4 ft. of the top.
Immediately underlying the bedplate, and with a view of making a perfectly level bed for the same, cast-iron blocks, 12 in. square and 4 in. thick, with a hole which only just admitted the head of the bolt, were placed, carefully levelled by instrument and set in cement, the spaces all round and between these being levelled to the thickness of 1 in. with cement. In addition to the round hole in each block, a slot was cut and a taper wedge driven hard into this and against the screw thread. This was done to prevent torsion in the bolts when the large upper nuts required to be drawn tight. On the bed thus prepared the lower bedplate was laid in the manner hereafter described. The heads of the holding-down bolts, as well as square washers, nuts, &c., are shown further on in connection with the bedplates.
Raising of the Approach Viaduct Girders, and Underbuilding of the Piers.
The height to which the piers of the approach viaducts had to be carried was 130 ft. 6 in. above high water, and the question how best to deal with both the erection of the girders and the building of the piers was ultimately settled by deciding to put the girders together at any convenient level, and make the lifting of these and the building of the masonry a simultaneous operation.
The fifteen spans of 168 ft. each, of a total weight of slightly over 3000 tons, or, roughly, 200 tons per span, were built under a sub-contract by Messrs. P. and W. McLellan, of Glasgow, the contract including their being put together and rivetted up on the staging provided at the Forth Bridge.
The girders are of the ordinary double-lattice girder type, consisting of two parallel girders at 10 ft. centres, having trough-shaped top and bottom booms and side bracings consisting of intersecting diagonal struts and ties. The trains run on the top, the troughs of the two outside rails forming the top booms of the girders. Each span is divided into eight bays of 21 ft. each, which is also the height of the girders, and at the intersection of struts and ties a vertical support is carried upwards to the top boom. A cross-bearer occurs every 7 ft., or three to each bay, and carries not only the two troughs for the inside rails, but also projects beyond the two outside troughs for a distance sufficient to form a 4-ft. path on each side, and to support the brackets of the wind fence. The floor is made up of buckle plates. The bottom booms of the girders are braced laterally by lattice girders intersecting at centre, and there are also vertical cross-bracings of double angles at suitable distances.
Two spans are made continuous, and expansion joints are provided over every second pier. The ends of all the girders rest on sliding bedplates, no rollers being used. The details of these girders call for no special remark. They were originally intended to be built of wrought iron, but, in view of the cheapness and excellent quality of steel, the latter material was ultimately adopted.
Various circumstances combined to fix the height of the staging on which these girders were put together.
On the Fife shore the high ground upon which the cantilever end pier and piers 10 and 11 were founded necessitated the putting up of staging to a height of 41 ft. above high water; the four piers 10 to 13 having by September 30, 1883, been brought up to 37 ft. above high water.
On this staging the girders were erected and rivetted up, the last length next to the north cantilever end pier and nearly half the length of the span between pier 13 and the abutment being left out, however, for the time being. The cantilever end pier had been built up to a considerable height, and between pier 13 and the abutment a public road passed at a considerable height above the then level of the staging.
As the mode of raising the girders will be more fully described in connection with the south approach viaduct, it will be sufficient to state here that, in order to raise the end of the girders nearest the cantilever end pier, a set of strong columns were built up and lengthened by degrees as the lifting proceeded; and upon these the hydraulic cylinders were placed. The mode of raising was similar to that employed for the large platforms of the central towers, and fully described there. Upon piers 10, 11, 12, and 13 the lifting proceeded in the usual way, but, not far from the abutment, a set of columns similar to those at the
