246 



THE CIVIL ENGINEER AND ARCHITECPS JOURNAL. 



[Junk, 



Shannon at Portumna, to form a communication between tlie counties of 

 Gahvav and Tipperary, at the spot where a timber bridge formerly stood. 

 The present structure is composed of straiglit cast iron girders, resting upon 

 piers formed of timber piles, leaving thirteen openings of IS feet 6 inches 

 span each, between the Tipperary shore and Hayes Island, and twelve open- 

 iiins of the same span, between the island and the outer pier of the swivel- 

 bridge, wliich is 40 feet G inches span, and is close to the Gahvay shore. The 

 total length of the bridge is 558 feet 6 inches, exchnive of the width of 

 Haves Island, upon the centre of which are placed the toll-house, and a stone 

 obelisk, commemorative of the building of the bridge, under the direction of 

 the Commissioners of the Public Works for Ireland. The width between the 

 balustrades is 17 feet. The ashlar work and ruhble masonry of the abut- 

 ments, the pier of the swivel-bridge, the toll-house, and the retaining walls, 

 are of Portumna limestone, and are built with hydraulic mortar, the lime of 

 which was burnt from the same description of stone as that used in the 

 building. In the foundations, the sheeting piles are of red pine; tne bear- 

 ing piles of beech and larch ; and the main piles and waling pieces for sup- 

 porting the roadway girders are of Memel timber. The eartli having been 

 excavated down to the solid strata, of sufficient space for the abutments, re- 

 taining walls, counterforts, and the foundations for the swivel bridge (the 

 latter being done by means of two coffer-dams) ; the foundation or bearing 

 piles 8 feet long and 10 inches in diameter, were driven 4 feet apart, from 

 centre to centre, along the foot of the abutment walls, and a capping of 

 Dantzic timber 12 inches by 6 inches was spiked to them ; the whole area of 

 the foundation under the walls and counterforts, was covered with a thick- 

 ness of 12 inches of concrete, composed of six parts of clean gravel and sand, 

 and one of lime. A course of flag-stones 7 inches thick, was then laid and 

 the walls were built, being backed with well pounded clay from the excava- 

 tions, as the masonry proceeded ; the space between the retaining walls was 

 then filled to the underside of the roadway, and levelled to receive the 

 broken stone or metalling. The ashlar work and backing, were laid flush in 

 their respective kinds of mortar, and every course was well grouted, so that 

 the whole might become one solid mass. The mortar was made of Portumna 

 lime, in the proportion of (wo parts of sand to one of lime, fine sifted and 

 wrought in a pug-mill. The main piles, 14 inches square, (after being 

 Kyanized,) were driven at least 9 feet into the solid ground, at distances of 

 20 feet apart from centre to centre, and w\re cut off level, at the height of 

 9 feet 6 inches from the surface of the summer water-level. The caps were 

 then tenoued upon them, all the joints having in them a sheet of patent felt 

 saturated with boded tar. The cast iron girders are 20 feet long, 1 7 inches 

 deep, and IJ inch thick, with a flanch at the top 8 inches v\ide, to receive 

 the roadway plates, and another at the bottom of 4 inches in width. They 

 are supported by chairs cast in the caps, and are secured by distance pieces. 

 The roadway plates are J inch thick, secured by bolts and nut>, and the 

 joints made with iron cement. Cast iron fascia plates are screwed to the 

 outside girders, to carry the wrought iron balustrade. 



Previously to leaving the manufactory of Messrs. J. and R, Mallet (Dub- 

 lin), where they were cast, all the girders were proved, by placing them on 

 supports 20 feet apart, and suspending from the upper edge a weight of 12 

 tons, which was made to traverse from end to end of the girder, in order to 

 subject each part to the same test. 



The swivel-bridge is composed of two leaves, with a clear opening of 40 

 feet for the navigable channel. The ribs forming the arched part of the 

 bridge, from the abutmeiit to the centre, are each cast in one piece, with 

 flanches at the radiating line, to which the cross tie-plate is bolted ; a con- 

 tinuation of each rib is carried across the upper frame, to the circular tie- 

 plate at the end ; these have also flanches to correspond with those of the 

 arched ribs, and are bolted together ; the flanches on the upper edge of the 

 ribs, receive the roadway planking, which is of British oak 2 J inches thick. 

 The leaves turn on case-hardened iron rollers, and require about 15 tons of 

 ballast, to balance them. The construction is minutely described, with the 

 quantity of materials of all kinds employed, the dimensions of the several 

 parts of the masonry, the timber work, and the cast and wrought iron 

 work. , 



The specifications, the form of tender, and the prices of the various por- 

 tions, are given, and it is stated that the total cost of the bridge, including 

 the extra work, superintendence, law expenses, &e., was ^24,131 8s. \d. 



Extracts from the journal of Mr. Smith, the superintendent of the works, 

 give the dates of the commencement and termination of the several parts, 

 from which it appears, that the first stone of the abutments was laid on th« 

 I3th September, 1838, and that the whole structure was finished on the 13th 

 January, 1842. 



WELLINGTON BRIDGE, NEAR AIRE. 



•' Account of the luilding of the ' Wellington' Bridge, over the river Aire, 

 at Leeds."'^ March 5, 1844. By John Timperley. 



This bridge was erected from the designs, and under the direction of the 

 late John llennie ; it is situated on the line of road leading from Leeds 

 towards Wortley and Armley, and spans the river Aire at a spot where it is 

 100 feet wide, and about 6 feet in depth ; the banks rising to between 7 feet 

 and 8 feet above the surface of the water. The borings, which were made to 

 the depth of 30 feet, on each shore, to prove the ground, previously to com- 



1 The discussion of this paper was extended through pwt of the meetings of March 5tb 

 and 12th, 



mencing the construction, showed the strata to consist of fine sand, and then 

 sand and gravel, with thin layers of what was supposed to be stone, but was 

 probably, hard concreted gravel, such as was afterwards found in excavating 

 for the foundations. That on the south bank, was commenced in the middle 

 of September, IS17. The upper part, for 6 or 7 feet in depth, was through 

 fine soft sand ; then came a bed of alluvial gravel, containing, at about 12 

 feet from the surface, black rotten wood, roots of trees, shells, hones, and 

 horns of animals. The upper part of this gravel was coarse and open, but it 

 gradually became finer and more compact, until it assumed the hardness of 

 a concreted mass, resembling agglomerate, very like (except in colour) the 

 Blackwall rock, which was taken up about forty years since, in deepening 

 the entrance from the Thames to the East and West India Docks. Upon 

 this stratum Mr. Rennie ordered the foundation to be placed, although it 

 was not so deep by 4 feet, as he had originally intended. 



The coffer-dam, which was formed of a double row of piles of half timbers, 

 from 15 feet to 18 feet in length, was then completed ; the best earth that 

 could he procured for the puddle, was of so liglit a nature, that iu high 

 freshes the leakage became so considerable, as to render it advisable to allow 

 the dam to fill with water, to prevent its blowing up. The details of the 

 construction of this coffer-dam are given. It was kept dry by a steam-engine 

 of C horses' power, which was fixed on the shore, and worked the pumps by 

 an endless chain. The quantity of water was such as to keep the pumps 

 constantly at work, night and day. The coffer-dam for the north bank was 

 constructed after the foundations on the south shore were finished. The 

 details are then given of the sheet piling and wales, &c., in front of the abut- 

 ments, which arc each 30 feet long, by 28 feet wide, at the bottom, dimin- 

 ishing by offsets to 27 feet in length, by 21 feet in width, at the springing of 

 the arch. 



The abutments are built in radiating courses within, but on the faces they 

 are horizontal ; the stones were from 14 inches to 18 inches thick, cut cor- 

 rectly from templates, made to suit the respective courses. The lowest 

 foundation courses were of large blocks, laid dry, and the joints well 

 grouted ; but the other courses, up to the ordinary water line, were laid in 

 mortar, made from magnesian limestone, got on the banks of the Aire, a few 

 miles above Ferry Bridge : the proportions were, one part of lime, one part 

 of clean sharp river-sand, and one part of forge scale, the whole well mixed 

 and tempered, and used quite hot. The grout was made from the same lime, 

 and was used for all tlie courses, except the lowest, where Parker's cement 

 was employed, which was also used for pointing all the face joints up as high 

 as the water-level. In the other parts of the ttructnre, the mortar was com- 

 posed of one part of lime to two parts of sand, but that for the arch was 

 made of equal proportions of lime and sand. Great care is stated to have 

 been taken with the joints, as no under-pinning was allowed, the beds of the 

 stones being all dressed to coincide accurately. The ordinary allowance was 

 Jth inch for each joint, but on trying the first fourteen courses, from the 

 springing, it was found, that 1 inch only was taken up by the joints, which 

 gave Tjth inch for each. The stones were laid on the south side by a 

 moveable crane, and on the north side from the end of the two-wheeled truck 

 (somewhat resembling a timber carriage) by which they were brought from 

 the stone-yard on the south bank, along a wooden tramway and temporary 

 bridge, extending from the south to the north shore, using either a simple 

 sling, or sheave-blocks, for placing the stones, according to their dimensions 

 and weight. The construction, dimensions, and cost of this truck and of the 

 crane are given in detail. 



The abutments being finished, the piles were driven, to support the centres, 

 which were fixed so high as to be above the freshes. The lagging was laid 

 5 inches higher than the proposed arch, to allow for it settlement. The six 

 centres were framed of Memel pine, each rib containing about 370 cubic feet 

 of timber. The striking-wedges were of seasoned oak, well greased ; they 

 were 6 inches wide and 9 inches in height altogether, the middle one, which 

 was the largest, being the striking wedge. They were, however, found to be 

 too narrow, for they were squeezed upwards of an inch into the timber, by 

 the weight of the centres and the masonry. Piiorto framing the centres, 

 one-half of the arch, which is a segment of a circle of 91 feet radius, with a 

 versed sine of 15 feet, was laid down, full size, upon a platform, from which 

 templates were made, for dressing the voussoirs and arcli-stones ; the front 

 voussoirs were 7 feet on the bed, at the springing, diminishing to 4 feet at 

 the crown ; but the interior arch-stones, near the springing, were much wider. 

 The arch-stones were, on an average, 3 feet long, by 18 inches thick. It 

 was customary, in setting the stones, to saturate them with water ; a thin 

 coat of mortar was laid on the under stone, the upper one was lowered, and 

 well beaten down while the mortar was soft ; the surfaces were thus brought 

 closely in contact with each other, and any interstices that remained, were 

 grouted, after the vertical joints had been pointed with cement. 



When the arch was turned to the extent of one-third from each side, about 

 20 tons of stone were piled on the crown, as an equipoise for the centres, 

 and the haunches were not loaded until the key-stones were placed. The 

 turning of the arch occupied four weeks ; when that was finished, the 

 haunches were completed, and the centres were eased ; but it was found that 

 the weight, which before the arch was keyed was equal to 1000 tons, had 

 forced the wedges into the timber, so as to render it necessary to cut some 

 of them out, which occupied three days for the first easing. A second easing 

 took place two days after, and after a third easing the centres were removed. 

 During the progress of the work, the arch squeezed down about 2i inches; 

 in a few days after the centres were struck, it settled li inch, which in- 

 creased slonly to 2i inches, after which do further subsidence was observed. 



