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THE CIVIL ENGINELR AND ARCHITECT'S JOURNAL. 



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i ag the pierp below the level of low water. Previous to tliis. the principal 

 cxialing bridges consisted of a number of small Goiliic or of circular arches, 

 wilh ron!;li piers of nmsoury built either upon a foundation of loose rubble 

 sioiies thrown prnmiscuously iuto the river until sufiicientij high and solid, 

 or upon timber plalfurnis resting upon piles surrounded by large bulwarks 

 of timber, tilled with loose stones, called starlings, which materially con- 

 tracted the water way where they were placed, and by causing increased 

 rapidity in the cunent, created great obstacles to the navigation, as well as 

 to the drainage of the adj-icent country. Of this, the wellknonn examples 

 of Old London Ilridge, those at Newcaslle-upO[i-T>ne, Kochester, and 

 Belfast, may be mentioned. All these, wilh the exception of Ifochester 

 Bridge, are now removed, and are replaced with others constructed upon 

 the modern improved principles. \V estniiuster Bridge was followed by 

 that of Blackfriars by Mylne (I7G0-71), consisting of nine semi-elliptical 

 arches, the largest of which is 100 feet span and 41 feet G inches rise; the 

 total length of the bridge is 99.5 feet, and 45 feet wide ; here the elliptical 

 nrch was introduced about the first time in this country. Smeaton's bridges 

 of Coldstream across the Tweed, in 1703, composed of five circular arches, 

 the largest of which is CI feet span ; that over the Tay at I'erth, in 1706, 

 of nine circular arches, the largest of which is 75 feet span ; at Hexham, 

 over the Tjne, in 1707, of nine circular arches, the largest of which is 52 

 feet span, and others, for that period, were works of considerable magni- 

 tude. These were followed by numerous smaller works all over the king- 

 dom, more remarkable for con\eoience and utility than for any peculiarity 

 in their construction worthy of notice, until in lS09-lbl7, when Waterloo 

 Bridge, across the Thames, consisting of nine equal semielliplical arches, 

 120 feet upon each, and 3j feet rise, was built ol granite in a style of solid- 

 ity and magnificence hitherto unknown ; there the elliptical arch, wilh in- 

 verted arches between tliem to counteract the lateral pressure, was carried 

 to a greater extent than in former bridges, and isolated coflFer dams upon a 

 great scale in a tidal river, with steam engines for pumping out the water, 

 were, it is believed for the first time, employed in this country ; the level 

 line of roadway, which adds so much to the beauty as well as the conve- 

 nience of the structure, was there adopted. The bridge across the Severn 

 at Gloucester, in I82S, by 'I'elford, is worthy of remark, as being the first 

 with one arch, of 150 feet span, like those of the bridge across the Seine at 

 Neuilly, near I'aris, by I'erronet, where the interior of the arch is elliptical 

 and the exterior circular. 



New London Bridge (1825-1831), consisting of five semi-elliptical arches, 

 viz., two of 130 feet, two of 140 feet, and the centre 152 feet 6 inches span, 

 and 37 feet ti inches rise, is perhaps the largest elliptical arch ever at- 

 tempted , the roadway is 52 feet wide. This bridge deserves remark on 

 account of the diflicnlt situation in which it was built, being immediately 

 above the Old Bridge, in a depth of from 25 feet to 30 feet at low water, 

 on a soft alluvial bottom, covered with large loose stones, scoured away by 

 the force of the current from the foundation of the Old Bridge, the whole 

 of which had to be removed by dredging, before the coH'er-dams for the 

 piers and abutments could be commenced, otherwise it would have been 

 tTclremely difficult, if not impracticable, to have made them water-tight; 

 the difficulty was further increased by the Old Bridge being left standing, 

 to accommod.ite the traffic, whilst the New Bridge was building, and the 

 restricted water-way of the Old Bridge occasioned such an increased ve- 

 locity of the current, as materially to retard the operations of the New 

 Bridge, and at times the tide threatened to carry away all before it. The 

 great magnitude aud extreme flatness of the arches demanded unusual 

 care in the selection of the materials, which were of the finest blue and 

 white granite from Scotland and Devonshire; great accuracy in the work- 

 manship was also indispensable. The piers and abutments stand upon 

 )jlatforms of timber resting upon piles about 20 t'eet long. The masonry 

 is from 8 feet to 10 feet below the bed of the river. 



I will conclude this division of the sulject with the celebrated bridge 

 across the Dee at Chester. It consists ot a single arch, the segment of a 

 circle 200 feel span, with a versed sine or rise of 42 feet, which is the lar- 

 gest stone arch upon record ; the arch stones at the crown are 4 ft. ti in. 

 deep, and 7 feet at the bpringing, and the abutments on both sides of the 

 river are founded on new red sandstone. The centre for building the arch 

 was remarkable for its simplicity, strength, and rigidity, by which meanj 

 the greatest ell'ect was iiroduced by the smallest ciuantity of timber, and 

 any change of form, so prejudicial in centres, was prevented. This line 

 structure is due (it is believed) to the combined talents and energies of the 

 late Mr. Harrison, the architect, of Chester, who made the original de- 

 sign ; to Mr. George lienuie, who equilibrated the arch, gave the proper 

 dimensions of the voussoirs and form and dimensions of the abutments, 

 the mode of constructing them, and designed the centre, the original model 

 of which is now in our gallery ; and to iilr. Jesse Hartley aud Mr. Trub- 

 ehaw, who worked out l!ie details, and carried the whole iuto eflect. 



A proper theory of the equilibrium of the arch, which shall satisfy all 

 the conditions of the question, when applied to practice, may be said to be 

 Siill wanting, though much valuable information may be derived from the 

 Ecientific works of Hiitioa, Atlwuod, Moseley, G wilt, aud others, on the 

 eubject. 



Oblique or skew bridges have but recently obtained extensive me 

 Chapman built some in Ireland many years ago, and wrote an account of 

 his mode of constructing them. On railways they were introduced by Sie- 

 phenson, and are now generally employed. Buck's excellent treati.se on 

 the principles aud practise of their construction greatly facilitated their 

 ezecution. 



Iron Bridges. 

 The introduction of cast iron for the construction of bridges commenced 

 about the year 1779, when that over the Severn, near Coalbrook Dale, by 

 Darby, was the first; it consists of a circular arch 100 feet span, and a 

 versed sine of 43 feet, approaching nearly to a semicircle ; the height of 

 the springing is 10 feet above low water, and the total height to the under- 

 side of the soffic is 55 feet ; the banks of the Severn being high, this form 

 accords well with them. It is formed by five ribs of cast iron, with per- 

 pendicular spandril pieces, resting upon them to support the roadway. 

 This, for a first attempt, is well adapted to the situation, and has answered 

 the purpose. This was followed by the bridge over the Wear, at Sunder- 

 land : the design for this was said originally to have been made by Thomas 

 Paine, the well-known political writer, and was cast at Kotherham, being 

 intended for erection in America; hut the materials were subsequently 

 employed in constructing Sunderland Bridge, under the direction of Wil- 

 son, in 1790, the idea having been suggested by Rowland Burdon. The 

 curve of the arch is that of a segment of a circle, the length of the chord 

 or span is 200 feet, and the versed sine or rise 30 feet, the total height 

 from low water to the underside of the soffit of the arch is nearlj 100 feet. 

 It consists of six ribs, each composed of 105 cast iron radiating pieces, 

 connected at the top and bottom by the circular pieces which form the 

 curve of the arch : these ribs are united in their transverse direction by 

 tie-pieces; the spandrils are filled in with cast iron circles, touching each 

 other at their circumferences, and supporting the roadway, which consists 

 of a strong frame of timber, planked over and covered with a cement of 

 tar and chalk, upon which a layer of marl limestone and gravel is placed. 

 The centre deserves notice on account of the difficulty and confined natuPB 

 of the situation, which rendered it necessary to preserve a constant passage 

 for ships wilh their standing rigging ; this was effected by a perpendicular 

 framing resting upon piles in the bed of the river, with a sufficient opening 

 on each side for the vessels. Upon the top of this perpendicular framing, 

 the transverse framing or centre for supporting the arch was fixed, and 

 answered its purpose well. Some time after the removal of the centre, the 

 arch was observed to swerve bodily in a horizontal direction to the east- 

 ward, forming a curve having a versed sine of about 12 or 18 inches; if 

 this had continued to increase, it would no doubt have soon occasioned the 

 downfall of the structure ; it w as, however, very skilfully remedied by the 

 introduction of transverse and diagonal tie-bars and braces, assisted by 

 wedges and screws, so that ultimately the whole was brought back and 

 secured in its original form and position, where it has since remained in a 

 substantial state without alteration. The width of the bridge is 30 feet ; 

 the abutments are of stone, founded on rock ; they are 24 feet thick, and 

 from 42 feet to 37 feet wide. This bridge, for boldness of the design and 

 construction, as well as for its elegance and lightness, must be considered 

 a work of peculiar merit ; particularly if the period in which it was con- 

 structed be remembered. 



About the same time, the bridge at Build was, across the Severn, by Tel- 

 ford, was erected. It consists of a single arch, segment of a circle, whose 

 chord or span is 130 feel, and versed sine or rise 27 feet, the deplh of the 

 iron frame forming the arch being 3 ft. 10 in. ; it consists of three ribs, 18 

 feet wide from out to out, connected together in their transverse direction 

 by tie-bars. The spandrils for supporting the roadway consist of vertical 

 pieces, resting upon the segments forming the arch ; the abutments are of 

 stone. There is a novelty in the construction of this bridge worthy of 

 remark. The two outer ribs consist of two segments of circles, each 

 struck from difl'erent centres, the crown of one terminating immediately 

 below the roadway, the other at the top of the parapet, so that the plat- 

 form forming the roadway is both suspended aud insistent. The object of 

 this being, it is presumed, to increase the depth of the truss supporting 

 the roadway, and thus to add to the strength of the bridge : but it was un- 

 necessary, and does not appear to have been adopted in any of Telford's 

 subsequent designs, which are numerous. Amongst them may be men- 

 tioned that of Bona, Tewkesbury bridge over the Severn, also that over 

 the Dee, near Corwen, &c. Bristol bridge over the Avon, by Jessop, is a 

 neat simple structure. Boston bridge, by Rennie, over the \l itham, of 

 lOU feet tpan, with a versed sine of 4 feet, is remarkable for its boldness 

 and lightness. The principle of coustruction resembles that of Sunderland, 

 but is an improvement upon it, in having a better system of transverse and 

 diagonal braces, and tiie spandrils consisting of vertical instead of circular 

 pieces. All these have, however, been far exceeded by the Soulhwark 

 bridge over the Thames, by Rennie. This consists of three arches, all seg- 

 ments of the same circle ; the centre arch is 240 feet span, with a versed 

 sine or rise of 24 feet, and the two side arches are 210 feet span each, with 

 a versed sine or rise of 18 ft. 10 in. each. The arches are formed 

 by eight solid ribs in each, and each nb consisting of fifteen pieces, C feet 

 deep at the crown of the arch, increasing to 8 feet deep at the springing, 

 2J inches thick in the middle, and 4^ at the top and bottom: these ribs are 

 connected together in their transverse directiou by cast iron tie-braces of 

 the same depth as tlie ribs, but open in the centre, and in the diagonal di- 

 rection by another series of ribs ; the whole of the segmental pieces form- 

 ing the arch, as well as the transverse and diagonal tie-braces, are kept tn 

 their places by dovetailed sockets and long cast iron vved^'es, so that bolts 

 for hoUiing the several pieces together are unnecessary, although they were 

 used during the coustruction of the bridge to keep the pieces in tber places 

 until the wedges had been driven. Thus the ribs formed, as it were, a 

 series of hollow masses or voussoirs similar to those of stone ; a principle 

 which it is believed is new in the coustruction of cast irou bridges, bat it 



