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 Suspension Bridge 
 
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 REPORT 
 
 OF 
 
 SAMUEL KEEFER 
 
 CTVIL ENGINEER. 
 
 TO THE 
 
 Fresidetit and Directors of the Js''iagara Falls Suspension 
 
 Bridge Company, and to the President and Directors 
 
 of the Clifton Suspension Bridge Company. 
 
 FEINTED BY ORDER OF THE DIRECTORS. 
 
 BBOCKVILLE, 0:STAIiIO, MARCH lat, 1869. 
 
^FF1CZF^3 
 
 OF 
 
 Under whom the Bridge was constructed in 1868. 
 
 -—*-• 
 
 Hon. JOHN T. BUSH, President, - - Clifton Place, Canada 
 DELOS Dw WOLF, Esq., Treasurer, - - - - 08WEG0, N. Y. 
 HOLLIS WHITE, Esq., Vice President, - Niagara Falls, N. Y. 
 W. G. FARGO, Esq., Director, - - - - Buffalo, N. Y, 
 VIVUS W. SMITH, Esq., Secretary, Auditor and 
 
 General Superintendent, - - - Stracuse, N. Y. 
 
 -♦- 
 
 SAMUEL KEEFER, Chief Engineer. 
 
 Member of the 'Ambmoah Society or Citil Bmoimekhs," and formerly Chief Xnglneer of 
 the Department of Public Works of Canada, etc. , etc. 
 
 » 
 
 Hon. WILLIAM J. McALPINE, Consulting Engineer. 
 
 President of the "Amkbicam Booibtt ov Civil ENoursxits," member of the " Inbtitutiov 
 
 OF Cini. ENononms," London, and formerly State Sngineer of New York, and Eng:i- 
 
 neer In Chief of the United States Dry Dock at Brooklyn, etc., etc. 
 
 ♦ 
 
 Capital stock authorized under Charter from the State of 
 
 New York, $200,000 00 
 
 Capital stock authorized under Charter from the Domin- 
 ion of Canada, - - 200,000 00 
 
 Total, $400,000 00 
 
 vf ^i 
 
-R-EiFoiEirrf. 
 
 To the President and J>irectora of the " Niagara Falls Sus- 
 pension Bridoe Company," and to the President and Direct- 
 ora of the " Clifton Suspension Bridge Company :" 
 
 Gentlemen — • 
 
 The bridge which I have had tlie honor of constructing for your 
 joint Companies was so far completed on the 4th January last as 
 to be opened on that day for public traffic. It has also been . 
 examined and approved for public use by the Government 
 Inspectors appointed by the State of New York and by the 
 Dominion of Canada. For your intbrmation I now submit the 
 following particulars in reference to its construction : 
 
 The wonderful structure completed by Mr. Boebling in 1855 — • 
 the only successful railway suspension bridge yet constructed 
 — ^has for a period of fourteen years fully answered the purpose 
 for which it was designed, *'. <»., to form a connecting liiik between 
 the Great Western Railway of Canada and the New York Cen- 
 tral. The freight and passenger trains of both roads are contin- 
 ually passing over it, only limited to a walking pace, or speed .of 
 five miles an hour. Its span is 821 feet 4 inches. 
 
 Your bridge has been designed, not for heavy traffic, like the 
 one below, but for the accommodation cliiefly of the pleasure 
 travel; for foot passengers, and for carriages employed by the visi- 
 tors to the Falls, as well as tor the local traffic between the five 
 small towns, Chippewa, Drummondville and Cli^n, on the 
 Canada side, and Niagara city (so called) and Niagara Falls, on 
 the New York side. 
 
 For this purpose it was assumed that the ordinary transitory 
 load of passengers and vehicles passing over it at any one time 
 
6 
 
 would seKloiM uxceoil lit'fv tons, wliilt) on sonio Mccasions it niii'lit 
 be as iiiueli as oiio liuiidrod tons. My lirst Wesij^n was for a loa«l 
 of 5(> tons, hut the lirid^o has Ijock huilt of adecjuatc streiigtli in 
 all its parts to sustain tlio <<reater ioad of 100 tons with safety. 
 It has a sinji^le track of ten feet in width, aftlirdin^ ample nxmi 
 tor a pedestrian to pass a earriaj^t f>r sleij^h at any jx^tint on the 
 suspended roadway, and hy the adoption of pro|»er regulations 
 tor the use of it, as provided hy the Canadian Act, will afford all 
 the acconuTifMJation the puhlic will retpiire tl)r many years to 
 come. 
 
 Situated oidy three hundred yards below the American Fall, 
 it is consequently ex[»f)sed in winter to the spray from that Fall, 
 drifting and freezing upf»n it. It was impossible to f(»rm any 
 just conception of the extent to which it might accumulate during 
 the winter months, or to decide ])ositively bef<>rehand whether it 
 would endanger its stability or not. Indeed, the |)osHibility of 
 maintaining any bridge of so great span in such (tlose proximity 
 to tlie Falls, was only a matter of opinion. F'rom this and other 
 considerations, your Engineer was limited in expenditure, and 
 the construction of the bridge was in some degree tentative, 
 but he had no fears of the result. Having built the Suspension 
 bridge over the Ottawa River, close to the Chaudiorc Falls, which 
 tor a quarter of a century has stood in that oxjxwed j)osition 
 without suttering the slightest injury from spray, lie ajjprehended 
 no danger from that cause. 
 
 From motives of economy, as well as to insure the speedy coni- 
 pletion of the work, and an immediate return for the outlay, the 
 bridge was built with a single track, and the towei-s construct d 
 of wood. But the towers can at any time be rejilaced by stone 
 or iron, and when this is done the bridge becomes a permanent 
 structure; and by tlie widening of the roadway, and the addition 
 of more ropes, all the accommodation that is needed can readily 
 be provided. When the towers are covered with corrugated 
 iron, as intended, and so protected against lire and the intluence 
 of the weather, they can be made to last for many years. 
 
 The bridge spans the gorge just below the cataract, command- 
 ing a view southward of both Falls, as well as of a portion of the 
 rapids above them, of Goat Island and Table Rock. Northward 
 the course of the river is traced lor two miles down to the Rail- 
 
wav Sii-^ponsiun l'>ri«lji('. wliicli, witii tlic trniiis <'n»Ksini; it, is 
 jdainly visililc tVniii tlic new briilp'. I lore the rivor turns to tlio 
 left and is lo8t t<> viow. 
 
 Tlic end rostin«i<>n tlio rij^lit hsvjik is sitiiatod in Porter's tjrovO'T 
 jit tlio toot of Niiij^ani street, three hundred yards helow the Ameri- 
 can Full. The end restinuj on the left hank lands u]K»n the iruiin 
 road riuininj^ alont^ the lumk of the river, and is one hundr(>d 
 yards below the Olit^on House, and three-»juarters (if a mile he- 
 low the (ireat lloi*se Shoe Fall, on the Canada side. 
 
 The niairnetie hearinn of the hridije is S. 4(» dei;. K., or nearlv 
 Southeast ami Nnrth-west. It crosses the river at right an«jjles 
 to its «;eneral C(nii*se at this ])oint. 
 
 A section of the river an the line of the hridj^e j^ives a distance 
 oflllM>feet froui rock to rock, at the to]» f>f the clitf, and 850 
 feet at the water's surface. The rock on the let^ hank is 175 feet 
 above the water, and on the ri«>;ht bank ISO t'eet. The American 
 Fall is 10-4 feet. On the Canada side the rock is covered M'ith 
 two feet of earth. It falls off perpendicularly fith'-t<»ur feet to the 
 debris which covers the foot, and slopes away to the water's e<l«ije. 
 On the American side it is covered with twenty feet of <lriff (clay, 
 santl and gravel,) which, when reuioved to nuike rctoin for the 
 towers, exposes a water-worn surface. Here the rock overhauf^ 
 souie ten feet, and the pbunb line strikes the top of the debris at 
 a distance of eijrhtv feet from the surface. 
 
 Iuime<liately beneath the bridfj;e the river is ISO feet deep, ami 
 the current Hows at the rate of four to tivc miles an hour. Its 
 surface is mottled with t<)am froui the Falls, and rippled by the 
 eddies which indicate its dei)th and power. 
 
 From the surface of the rock to the top of the clitf, the ««;round 
 rises eiglity feet to tlie level of the table-huid, an<l attains that 
 elevation at a distance of a ([uarter of a nn'le from the river on 
 either side, showing that before the river had excavated its chan- 
 nel through its rocky bed, it flowe«l in a valley of more than four 
 times its present widtli. 
 
 GEXERAL DTilENSIOXSk 
 
 The span between the points of suspension, or centres of 
 towers, is 1,2G8 feet and 4 inclies. The deflection of the cables 
 at centre, or greatest depression below the horizontal line, varies 
 
8 
 
 from 89 feot in winter to 92 tbet in summer. The ilifteronco of 
 three feet iH owing to the ofibcts prcHhured ujxm th(Mn hy chmiges 
 of toniponitiire, ranging through one liun<lrcMl (K»gree« <»f Fjihron- 
 heit. 
 
 Tlie roadway is BU9j)ondo<J at an elevation of 183 feet above 
 the water on the Canada side, and 188 feet on the New York 
 side, while the centre, according to tliQ season, varies from liM) 
 to 193 feet, there being a rise of four feet in the curvature of the 
 bridge in summer, and of seven feet in M'intcr. The toj>s of the 
 towers being in the same horizontal plan, are therefore l<>r> feet 
 high on the letl bank, and 100 feet high on tlie right bank. 
 
 The length of tl»e cables at medium temj>eratnre is 128G feet 
 between the centres of towers, 1828 feet between the anchor j)ins, 
 where tliey are connected with the anchor chains, and 1888 feet 
 in all, between tl»e anchors end)edded in the masonry on either 
 side. 
 
 The prf>h>ngation of the cables under gror.nd is effected by 
 anclior chains ot Lownuxir Iron thirty feet in length, in links of 
 ten feet each, tinnly built in hydraulic masonry. 
 
 THK OI'ERATIONS. 
 
 When 1 v/as appointed your Chief Engineer on the ITth June, 
 1867, the locatif>n had previously been made, and the work com- 
 menced by stripping the rock on both sides for the seats of the 
 towers. Having fixed upon the line, and laid out ujK>n the 
 groHud the j»osition9 for the towers and anchorages, and fnrnished 
 plans ami written instructions fijr the guidance of my assistant, 
 by your re(piest I proceeded to England in August, 1807, tor the 
 purpose of procuring the necessary material. 
 
 It was at first proixjsed to use steel ropes for the cables, and the 
 choice between steel and charcoal iron was left to my discretion; 
 but upon making encpiiries in England, I was induced to relin- 
 quish the idea of employmg steel. In a work so hastily under- 
 taken, and proceeded with so rapidly, there was no time to 
 institute the tests and enquiries necessary to settle the question as 
 to the dependence to be placed upon it; and, as at the outset 
 there was plainly no saving of cost, it was considered best to 
 adhere to a material which up to this time had proved reliable. 
 Accordingly all the ropes for the bridge were made of the best 
 charcoal iron wire. These and the tension plates for the under- 
 
ground uiiclior chains were muniifactured in England tomyonier, 
 and ftliippcil tor (.'uiuida bt'turo the cloee of the year, and I 
 returned home in November. 
 
 Durinf^ my ahHence the t^iwers wore framed and erected, and 
 Bonie progress was niarle with the anchorages. By your orders 
 the works were su.speiide<l early in October, and were not gener- 
 ally resumed until the tollowing month of May, 1868. Advan- 
 tage, however, was taken of an ice-bridge ti>rmed in the month of 
 February, for the taking across the two carrier ropes sulwequently 
 used tor the erection of the bridge. This feat was accomplished 
 with economy and dispatch, under the personal superintendence 
 of your President. 
 
 The winter months wen? occupied by your Engineer at Brock- 
 ville, in maturing his plans and making his calculations for the 
 next season's operations. 
 
 It was first intended to me the Erie and Ontario Railway for 
 uncoiling the cable ropes, but when it could not be leased, the 
 ropes were 8j)un out from a turn-table, upon a tem}X)rary plat- 
 form, laid down for that purjx^e, where they were examined, 
 cleaned, ]>ainted, strained and marked; and then run down the 
 hiil until the leading end, with the yoke attached tr> it, reached 
 the anchorage. 
 
 The ropes had been so well saturated in linseed oil, that it 
 filled up all the pores between the wires, but where exposed on 
 the outside, the oil, in places, was rubbed off, and oxidation had 
 commenced. When cleaned they received a good coating of 
 paint, consisting (►f the red oxide of iron mixed with l)oiled lin- 
 seed oil, and a second coat was added after they were suspended 
 between the towers. 
 
 A base line of 1800 feet was accurately nieasured off upon the . 
 platform by means of a pine rod fifty feet in length, the same 
 that had been used for measuring the base from which the span 
 of the bridge had been determined. 
 
 In order that the levels for the bridge might be arranged with 
 some degree of accuracy, it was necessary to know beforehand 
 how much the roj»e would stretch when loaded wiih the bridge. 
 There being no facts to establish the law of elongation in Bolid 
 wire ropes of this description <ier different degrees of strains, 
 it was determined by direct ex^ \ 
 
 I) , 
 
1^ 
 
 For til is purpose the weight of the rope itself, by its deflection 
 between two supports 300 feet apart and moving freely on rollers, 
 was used as a measure of the j»ower applied to stretch it on the 
 platform — the deflection being a function of that power. The 
 rope when strained by its own weight between the two towers is 
 subject, by calculation, to a strain of ten tons net. The elonga- 
 tion under ten and flftccn tfuis was noted. In this wav it was 
 satisfactorily Jiscertained that a power f»f ten tr»ns produced an 
 elongation of eight inches in 1800 feet of the ro])e. This result 
 agrees very nearly with Mr. Iloebling's experiments on single 
 wires, according to which he found, that, ''iron wire stretches 
 1 -j- 10,000 part of its length for every gross ton of 2240 pounds per 
 square inch of section." 
 
 Every rope was stretched upon the platform with a power ot 
 ten tons, and under that strain was marked at both ends and in 
 the middle of the 1800 feet. When released from strain the re- 
 coil was measured. At the same time the state of the thermom- 
 eter, then ranging from 95 to 115 deg. in the sun, (it being the hot 
 month of July,) was observed and recorded. Then these 
 elements : The initial elongation of 8 inches in 1,800 feet under 
 ten tons strain — the marks under that strain, and the observed 
 temperature reduced to a common standard of 110 deg., furnished 
 the basis of a calculation by which the absolute length of each 
 roi)e, imder any degree of temperature and tensile strain could 
 be definitely ascertained. 
 
 Having been marked under the same strain of ten tons, to 
 which, by calcidation, they are subject when hanging freely l)e- 
 tw-een the towers, and that force having stretched them 8 inches, 
 then an additional strain of twenty tons would stretch them 
 sixteen inches, and the ropes were accordingly cut so much 
 shorter than the mark. The importance of this correction will 
 be better understood when it is known that as the bridge is con- 
 structed the lines of curvature are always above the straight line, 
 and are pleasing to the eye, whereas, if the ropes had not been 
 so shortened, they would at certain seasons fall below it, present- 
 ing a reverse curve, at once offensive to the eye and injurious to 
 the stnicture. 
 
 The carrier ropes having been raised into position on the tojjs 
 f>f its towers, and set in large sheaves that jjrevented any lateral 
 stress upon them, and other sheaves, in pairs, placed also on the 
 
11 
 
 towei-s, close siloiigaido the saddles, the cable ropes were all suc- 
 cessfully taken r)ver in these, and on the carrier ropes, and were 
 then cut, yoked, anchored and regulated to ihe same degree of 
 detiection. After a second coat of paint, they were temporarily 
 clamped in cable form. 
 
 While engaged in these operations, the Chinese Embassy 
 visited the Niagara Falls, and by request of your Vice-President 
 I had the ]>lea8ure of taking over the Ambassador and his Eng- 
 lish Secretary in one of the "buggies" used in the construction. 
 This buggy, as you are aware, runs upon a single wheel uix)n 
 one of the carrier ropes. I accompanied them from the East to 
 the West tower, and back again, delighting his Celestial Highness 
 with the sublimity of the view and the novelty of the adventure* 
 
 The carrier ropes, with the "buggies" and "cradles" nmning 
 upon them, afforded the means of readily attaching the cable 
 buiuls and suspcndei-s, and as soon as this was effected, the hang- 
 ing of the roadway was proceeded with as rapidly as possible. 
 As the season advanced, the work was a good deal delayed by 
 winds and rain, and the ]>remature setting in of winter. Still, 
 notwitlistauding these hindrances, we succeeded in joining the 
 framework of tlie tlr)or at the middle of the bridge by the 15th 
 October, and from that time forward, convenient and unintM"- 
 rupted communication was estaljlished and maintained for the 
 workmen between the opposite banks of the river. It was 
 opened for tratlie on the -tth January last. Deducting the time 
 during which the works were suspended, we find that this, the 
 longest-spanne<l bridge yet erected, has been constructed in 
 twelve months of working time, which nnist be acknowledged a 
 very short time t(>r the accomplishment of a w^ork involving 
 every princi2)le aiul demanding all the care and consideration of 
 one of ten times the cost, especially under the ditiiculty of ol> 
 taining skilled labor, and (kf procuring materials from a distance. 
 
 Your board havinjj wiselv determined not to let the work bv 
 contract, the responsibility of selecting materials and directing 
 the operations rested entirely with your Engineer. He considers 
 himself fortunate in having secured the services of Mr. E. F.Far- 
 rington, as superintendent of construction during the most critical 
 and important part, since the month of June, 1868, and by 
 whom, with the assistance of an intelligent and faitliful body of 
 
13 
 
 niechuiiics and vvorkiiien, his i»lans have been carried out t<» his 
 entire Hatisfaction; and it affords him sincere gratification to be 
 able to state that this ditticult and hazardous achievement Inis 
 been accomplished without failure or accident of any kind. 
 
 The cost ()f the Ijridge when completed, including purchase of 
 land and prelimiiuiry expenses, will be about $150,000, U. S. 
 currency. 
 
 U])on submitting my plans tor your approval in April last, 
 the Directors very naturally, and, ^s I tliought, very properly 
 proposed to have the opinion of the highest professional author- 
 ity in America on such a bold undertaking. To this your En- 
 gineer cf»rdially assented, and by mutual consent my plans and 
 calculations were submitted to the Hon. William J. McAlpine, 
 late cliief Engineer of the United States dry dock in Brooklyn, 
 State Engineer of New York, President of the American Society 
 of Civil Engineei*s, &c., &c. By this reference your Board Wiis 
 at once Jissured, and your Engineer gratified, by the entire aj> 
 proval of the design by an Engineer of his acknowledged stand- 
 ing, sound judgment, and varietl experience. At his subsequent 
 visits the works themselves met his approval, and as evidence of 
 his opinion his final repoi-t since the opening of the bridge is ap- 
 pended to this. 
 
 The inspection required by the charter from the State of New- 
 York was made by Judge Gardiner on the 16th January. That 
 required by the Canadian charter was made by the Hon. Hamil- 
 ton H. Killaly, C. E., M. A., late President of the Board of Pub- 
 lic Works, Canada, on the 25th January. Copies of their re- 
 spective rejwrts are also appended. 
 
 • It was a matter of great importance that the calculations for 
 the strength of the bridge should be determined with perfect 
 accuracy in accordance with dearlv established scientific princi- 
 pies. Special attention was devoted to this branch of the subject, 
 and it was very gratifying to me to have my calculations verified 
 by an accomplished mathematician, the Rev. Edmund John 
 Senkler, M. A. Cambridge, of Brock ville, Ontario, who from his 
 pure love of analytical investigations, requested the favor, and took 
 upon himself tlie trouble of testing the results by independent 
 methods 
 
 The following particulars in reference to the strength of the 
 bridge are added for the information of the directors : 
 
18 
 
 I. — ^TIIK LOVD. 
 
 Tlie welglit of the suspended }>ortioii of the bridge between 
 tlie towers, including tlie cables, the roadway, the stays, stay 
 braces, bridle stays, suspenders and guys is 263 tons of 2000. 
 This constitutes the permanent load. The ordinary moving load, 
 as before stated, is fifty tons, and the extraordinary load 100 tons. 
 This is equal ti the weight of 1300 people, or one man to every 
 scpiare yard of the platform; or it is etpial to a load of thirty 
 carriages and three hundred peoj>le. This is assumed as the 
 transitory load. The permanent and transitory loads will not 
 exceed 363 tons. This load is supported by the united strength 
 of the cables and stays. 
 
 II. THE CABLES. 
 
 Tliere are two cables, one on each side of the bridge, descend- 
 ing to the level of the roadway at the middle, where tliey are 
 twelve feet apart between the centres, while at the towers they 
 are 42 feet apart — the sway on each side being iitleen feet from 
 the perpendicular. Their vertical defiection at medium temper- 
 ature is 91 feet, but in the plane of tlie swayed cable it is 92.22 
 feet. The horizontal projection of the cables or birds-eye view 
 from above, represents the landward portions as tangential to the 
 curve between the towers which is formed by swaying them in 
 at the centre. The angle of depression from the points of sus- 
 pension varies so little on either side of the towers, that the result- 
 ant of all the forces in both horizontal and vertical planes, 
 produces only a direct vertical pressure upon the towers. The 
 suspended system has in fact been so arranged as to exert no 
 lateral strain upon them, excej^t that which is unavoidable from 
 the force of the wind, and this, it Mill be seen, is modified to a 
 considerable extent bv the manner in which the cables are in- 
 clined tosrether at the centre, but more eftectuallv met and neu- 
 tralized by the use of stays and guys. Where the cables pass 
 over the towers there is necessarily a movement of three inches 
 arising from atmospheric changes; but the cables rest in cast-iron 
 saddles which move freely upon rollers interposed between them 
 and the cast-iron cap which crowns the summit of the tower, and 
 in this way the irresistible force of contraction is eluded. 
 
 Each cable is composed of seven ropes, each rope of seven 
 strand^s, and each strand of nineteen wires 0.155 inch indiame'er, 
 
rji 
 
 14 
 
 tliis size being between No. 8 and No. I) of tlie Birminn;liani wire 
 gauge. By a new process all the wires wore drawn of sufHciont 
 length (1910 feet,) to make one rope without s[>lice or weld from 
 end to end. There are 133 wires in eacli rope, and 931 wire?* in 
 eacli cable. The ropes are 2h inches in diameter, Ti inches in 
 circumference, and weiglit 54 pounds to the fathom. The calcu- 
 lated breaking strain of one of these rojies is 121 tons net. The 
 giuiranteed breaking strain was 100 gn>ss tons = 112 not tons, and 
 they bore the test of 108 tons net without tractiiro — the fasten- 
 ings having given way under that stniiii. 
 
 When a solid rope of this kind is subujittod to a dead [)ullj 
 the central strand being straight, while the (»thors are si)irally ar 
 ranged around it, it is the first to feel it, and would, were they 
 all alike, be the lirst to break. To obviate this unocpial stress 
 upon the strands, it is usual to put a liompon core in ro[)es used 
 for naval pur]>ose9. In our case a solid rope is wanted, and the 
 central strand is made of softer wire than the other strands. The 
 soft wire havius "greater ductilitv will stretch until the surround- 
 ing strands are brought to full tension, and thoy will then all pull 
 evenl}' together. 
 
 If any one thinks it an easv matter to lav hold of a rope of 121 
 tons strength and fairly break it, just lot him try it. lie will find 
 that all the- fastenings heretofore used are either too complicated 
 or too weak. The rope will render round the eye, or break in 
 the splice or socket before the full power is reached. A piece of 
 rope of this description was submitted for trial at the Liverpool 
 testing machine at Birkenhead. The maker of it secured one 
 end after his own plan, your Elngineer the other. The former 
 doubled one end round a cast-iron eye 14 i inches in diameter, 
 and fastened it by means of four heavy screw clamps to the main 
 rope. The clamj^s were made of CxlJ inch iron, leaving six 
 inches of space between them. This fastening had a very impos- 
 ing look. Your Engineer had the other end fastened in a 
 wrought-iron conical socket six inches Ions;, 2i inches in diame- 
 ter at one end, and Sh inches at the other. The end of the rope 
 was drawn through this socket and protrude<l 1 h inches above its 
 rim. The v,-ire9 were se]3arated and steel |)oints driven between 
 them, completely filling uj) the socket. Finally, the. ends of the 
 wires were bent and hammered down over them ; this enlarsins 
 
La 
 
 ( 
 
 / 
 
 or crowning of tlie roj,e being intended to keej> it from ]>nlHno' 
 out of the boU-shajied soeket. 
 
 At t\\Q first triiil, the clamps, under a .train of 36 tons, hegjin \ 
 
 to move towards the eye. At 50 tons the}' began to touch each 
 (tther; at 57 i tons they were in two pairs, witli inches of 8j)ace 
 between them, and the eye liad turned round 45 degrees. The 
 trial couhJ go no further. Tlie other end stf>od h'rm, and tlie rope 
 was uninjured. 
 
 At tlie second trial both ends M'ere fastened in the same man- 
 ner in sockets, but one of them pulled out under a strain of 88 i 
 tons, owing to insufliciefit fastem'ng. 
 
 At the third trial the r()])e bore a strain of 96 i tons gross, = 
 108 tons net, withe uit breaking, but the end pulled through the 
 socket, and the recoil injured it so much that the trial could not 
 be repeated. This test gave 96 J per cent, of the guaranteed 
 strength. 
 
 It was desiraltle, if possible, to tind a mode of fastening that 
 would give 100 ])er cent, of the strength of the rope. Ilavin"- 
 witnessed several experiments on spliced ropes of a smaller size, 
 I found they always broke in the splice before their full power 
 was reached. None of the methods heretofore used gave assur- 
 ance of holding. On my return to Canada the following experi- 
 ment was made : One eiul of a rope was fastened in the usual 
 manner in a wrought-iron socket, the other end in a cast-iron 
 yoke, and at every trial the end fastened in the socket was the 
 first to give way. The result was decidedly in favor of the yoke. 
 Tlie yoke is simply an elongated eccentric, the least diameter of 
 which is about twice the circumference of the ro])e, and the 
 length about three times the diameter. There are two holes at 
 the upper enlarged end, one of which is cylindrical, and of the 
 same size as the rope; the other conical, into which the end is 
 tastened as in the socket. The r^pe is passed through the cylin- 
 drical hole, then round the eccentric in a hollow groove, and 
 then fastened in the usual manner in the conical socket. 
 
 The jwint of attachment being eccentric, near to one side of 
 the yoke, it falls directly in line with the rope as soon as it is sub- 
 mitted to strain. The eye of this yoke is slotted to allow of a 
 movement of six inches for adjusting the ropes when suspended. 
 It is obrious, trom mechanical considerations, that if the tastening 
 
16 
 
 in tho socket end of the yoke ia only 25 per cent, of the hreaking 
 strength of tho rope, tho r<)i)e must be fairly broken before tho 
 fastening will give way. Jhit since fully 90 i per cent, can bo 
 connted on, as decided by the Ijirkcidiciul tost, it is (piito impos- 
 sible for the fastening to yield before the rojio breaks. There- 
 fore, by adopting this plan, tlie full strength of the rope can be 
 relied upon. For suspension bridges, more especially, tho inij>ort 
 ance of this device can scarcely be overrated. The ropes were 
 adjusted at the centre with the greatest facility by means of tho 
 slot, and with perfect confidence in the nnvielding nature of the 
 fastenings at either end. 
 
 At the anchorage the ropes are connected with the under- 
 ground anchor chains by means of adjusting links of 4, 8i and 13 
 feet in length of an nnifonn section of C x 1 inches. Three of the 
 yokes are in the direct line of tension, two are thrown down, and 
 two up, in order that all the ropes may be gathered into cable 
 form and clamped as nearly as possible to the i)oint of attacli- 
 ment. Tlie solid sectional area of the cables is 37.8 square 
 inches; that of the anchor chains 84 scpiare inches. The aggre- 
 gate force, or ultimate strength of both cables, 121 x 14 -- 1,094 
 tons net; that of the Lowmoor anclior chains 84 x 32, — 2,088 tons 
 net. 
 
 The ropes of which the cables were made were manufactured 
 by R. S. Newall & Co., of Gateshead-on-Tyne, from wires drawn 
 by Messrs. Richard Johnson & Nej)hew, of Manchester. Wires 
 of 1,910 feet in length were made whole, without weld joint, or 
 splice. The rods were rolled from the billets by one operation in 
 less than a minute. Billets weighhig 140 lbs., 1.5 feet long and 
 II inches square, were heated to a white heat in a gas furnace, 
 and passed through a series of rollers set close to the furnace, 
 until they were gradually reduced to rods of Ko. 3, B. W. G. 
 One end of the billet was in the furnace, while the other end was 
 being wound upon the reel. The rods were then drawn thrr»ngh 
 three holes down to the required size of 0.155 inch diameter. 
 
 As they were required to bear a tensile strain before break- 
 ing of 100,000 lbs. to the square inch, tests were made from 
 time to time as they were run oft', and a daily register was kept 
 of the results, of which the manufacturers have furnished me a 
 copy. By this register it appears that a few ot the wires fell 
 
17 
 
 short of the .spccititMl strongtli, but that nearly all <»t' them ex- 
 ceeded it. Some of these, it appeai-s, were drawn to go hij^^h a 
 degree of tension as 1 '20,000 lbs., an determined by direet 
 weights and lever jKiwer, while by the hylraulie test the strength 
 was mueh greater. 
 
 The ropes are beautiful h])eeimens ot the art of rope-nuiking. 
 For their size they possess u wonderful tlexihility, and there can 
 be no doubt of their having been fabricated of tiie best <juality 
 ofjiiaterial. 
 
 III. — THK STAYS. • 
 
 While they serve to stiffen the roadway and prevent oscilla- 
 tions and un<lulations, the stays are a real support to the bridge. 
 They form as it were, two rigid and powerful brackets extending 
 out from either shore half-way to the centre, and cary one half 
 the weight, and one-half the load; while they relieve the cables 
 of half their duty, the two systems are nevertheless so arranged 
 as to work in harmony — the primary object of the construction 
 being, so to combine the two independent systems as to make 
 them act in concert the moment a load comes upon the bridge. 
 
 There are twelve stays on each (Quarter, forty-eight in all. They 
 are carried back to the anchorage, and secured there to the same 
 anchors and in the same manner as the cables, save as regards 
 the method of adjustment, which, for the stays, is effected at the 
 other end by means of a nut and screw. 
 
 The longest stay is tangential to the curve of the cable at the 
 point of suspension; the rest fall within this angle, and are 
 attached to the platform at intervals of twenty-five feet. They 
 are of various sizes, according to position and the stress they have 
 to bear. The three outermost stays are made of 4i inch rope of 
 45 tons ultimate strength — the next six of 3i inch rope of 25 tons 
 strength — and the last three of 3 inch rope of 18 tons strength. 
 
 The whole ot the twelve ropes on each quarter are united with 
 seven landward ropes, that are bound up into one cable of tour 
 inches in diameter, and reach from the anchorage to the towers, 
 over which they are carried by saddles and rollers independently 
 of the cables. The three largest ropes pass over the towers un- 
 broken from the anchorage to the roadway — the next six are 
 coupled, or yoked to three of the largest ropes on the river side 
 of the towers, and the last three are joined to one of the largest 
 
IS 
 
 ropes on the same side. The rjist-iron yoke is use<l at both ends 
 f>t' the stays. 
 
 The aggre«j;:ite strength of the whole assemhhige of stays, 48 
 ill niimher, is 1344- toil'* net. By the rosohition of torcos this 
 affords 628 J tons of vertical lifting power. 
 
 Riverward, the stays pass in straight lines, directly from tlie 
 saddle to the roadway, passing down the inclined plane formed 
 ])y the suspenders, and to which they are seized at the crossings. 
 Landward, they are stayed to the cahles; and since contraction 
 'and expansion, under the van'ous clianges of temj)erature, nuist 
 affect them e<pially, they must always preserve their same rela- 
 ti\e position, and conse«[uently must always bear the same share 
 of the load. • 
 
 The mechanical advantage of empktying stays in this manner 
 is obvious, and the economy of the tarrangcment is conspicuous. 
 One hundred and twenty tons of wire rope were employed in the 
 fabrication of the cables, and only twenty -five tons in making the 
 stays. Both carrying an equal load, i\\u\ both strained to the 
 same degree, it iippears that one ton of stays is ecpud iii effect to 
 nearly five tons of cable! 
 
 Four stay -braces of three inch rope arc placed horizontally 
 between the cables, binding them together above the roadway to 
 keep them from swaying about; and four bridle stays aie 
 attached to the cables reaching from the rock at the base of the 
 towel's to a distance of 110 feet out upon the cables, and serving 
 to check vibration caused by the wind or by a moving loa«l. 
 
 IV. THE SITSPENDKHS. 
 
 The suspenders arc made of wire rope § inch diameter — two 
 inches in circumference, and ten tons ultimate strength. Being 
 placed five feet apart, there are 480 suspenders of 4800 tons 
 ultinuite strength, which is more than thirteen times the load 
 they have to sustain. The ends are crowned in wronght-ir«jn 
 sockets, connecting above to the cable bands, and below to the ten- 
 sion bolts that pass through the fioor beams and hold up the 
 bridge. Towards tlie middle of the bridge, where the suspenders 
 are short, all of less than twelve feet in length are made of solid 
 rods of Lowmoor iron i inch in diameter. All the tension bolts 
 are terminated by a screw six inches long, to admit of adjust- 
 ment. 
 
19 
 
 V. — TlfK GlYS. 
 
 The ovcrtlow stuvts, Ijy virtue of tlieir inclined position, have a 
 very good ettect in preventing lateral movement in the suspend- 
 ed rouihvay, hut the undei-tl(K>r gU3s offer a more direct resistance 
 to it. They check i>otii the verticd and transverse motion. As 
 fur as hoth stays and guys reach, /.«.'., half-way t<> tlie centre, there 
 is little or no vihratiun. Heyond this tlic guys alone extend two- 
 thirds of the way to the centre, and owing to their great length 
 there must necessarily ho some movement, but it is limited to 
 the expansi(Mi of the nuiterial. from changes of temperature, and 
 to the sagging of the rope under different degiees of strain. 
 Within these limits tiio wind can sway the platform, but it can 
 do no harm. . , • 
 
 The number of guys attaciied is fifty-four. Of these twenty- 
 eight are on the upstream and twenty-six on the downstream 
 side, the wind being stronger down than up the river. Some go 
 out horizontally to the top of the ('iff, some go down vertically, 
 hut the greater numbc^r occupy an inclined position, reaching 
 down to large boulders embedded in tlie slope of the bank. In 
 Spring it is iiitendeil to add a few more guys, stretching all the 
 way to the centre, w ith compensating adjustment for changes of 
 temperature. 
 
 These guys are made of the same size rope as that used tor the 
 suspenders. Atogether, they contain a reserve power of 540 
 tons, and offer a resistance of 200 tons to the wind, whichever 
 way it blows ; and yet, to all appearance they are mere gossamer 
 threads, scarcely visible to the naked eve. 
 
 The ropes used for the stays, susj^enders an<l guys, were manu- 
 factured by the Queen's Ferry "Wire Rope Company, from wires 
 drawn by Rylands Brothers, of Warrington. They were drawn 
 from charcoal iron of the sai-ic quality as that used for the cables, 
 and both at Birkenhead and Niagara Falls bore tests that were 
 perfectly satisfactory. They are /ill of superior (piality. 
 
 VI. THE TOWEIiS. 
 
 On each side of the river are twin towel's, constructed of white 
 pine of superior quality. Each tower presents the outline of a 
 tuncated pyramid, 28 feet square at the base, and 4 feet square 
 at the top. They are placed 13 feet apart at base, and the road- 
 
so 
 
 way jJttHKOS l)Ct\vorn tliom. They arc 105 foot high on tho Can- 
 ada sidt' and KX) foot on tho New York sido. Tlioy uro ])uilt up 
 of four tiinl>ors 12xlti inchos in each (•(►rner of tho pyramid, 
 iJ'avin^ a sj)aco of ono inch liotwcon thoni for vontihition, 
 through whicli tlio connoi-ting holts pasH. Ilori/ontal girths 1) x 12 
 inchos bind thcni together at every ten feet in hciglit, and 
 above tlie roadway these girtlia extend all across, l)inding the 
 two pyramids together into one tower. A series of heavy dia- 
 gonal traces on all four sides, cf»nd)ined with the girtlis, and Vmt- 
 tled together, servo to keep the ]>ost9 fairly in lino, and prevent 
 any lateral bending or vil)ration. The lower ends of these tim- 
 bers are stepped into cast-iron shoes, having cells for tho re- 
 ception of each p<>st. The 8hr)es are set in the solid sock in beds 
 rut out fairly to receive them at right angles to the direction of 
 the posts. The 16 timbers of the 4 ])08ts all come together at the 
 top, wliero they arc crowned by a heavy cast-iron cap having 10 
 colls on tho under sido to receive them individually, and deep 
 flanges on tho ujipor side, forming channels for tho reception o' 
 the saddles and rollers which carry tho cables and stays. The 
 timbers break joints with each other, and arc finidy bottled to- 
 gether. Wrought-iron plates, l-12th of an inch thick, with cen- 
 tral dowels, are i,iscrted in every butt joint. Tiie posts are so 
 finnly built and braced as to warrant their being considered in de- 
 tail, as short s(piare pillars or struts, having a breadth of base 
 equal to one-fifth their height, and tlierefore not liable to bending 
 under a heavy load. The mode of framing, too, cuts so lightly 
 into the wood, that every single piece of timber of 12 x 12 inches 
 may be taken as having an effective sectional area of 12 x 11, =• 
 132 square inchos. 
 
 The crushing force of white pine being about 5,000 lbs to the 
 S(juare inch, or 2i tons net, the weight required to crush down 
 one of the towers will be 132 x 32 x 2i, = 10,560 tons, or forty 
 times the weight of the permanent load it has to carry. 
 
 The effective strength of pine is estimated at one-tenth of its 
 crushing force, and hence tiie towers should be able to bear a 
 
 load of ~^, -= 1,056 tons. This is four times as much as the 
 
 111 ' ' 
 
 permanent load, q,nd three times as much as both the permanent 
 and transitory load taken together. 
 
 Should occasion rei:][uirc it, it will therefore be perfectly safe to 
 
SI 
 
 take out any oiio of the fi»ur tinibcrH oftlie eight corner poetg and 
 replace it bv aiiotlier, and the mode of framing jul<>j>to<l admitting 
 of it, the change can at anytime l»o nun U* without nuich diffi- 
 culty. 
 
 VII. — TUF, KOADWAY 
 
 t 
 
 At the centre, the curve of the n)adwiiy rison four feet alx)Vo 
 its chord in Summer and seven feet in Winter, there heing a riae 
 and fall of three feet due to the changes of temperature alone. 
 The chord line is not in a horizontal j>lane. The end resting on 
 the right hank is five feet the highest, hut in so great a span the 
 difference is inii)erceptihle. • 
 
 The two ends of the roadway are fixed to the nx;k on either 
 side, but the middle must necessarilv rise and full the three feet 
 just stated. The framing is therefore adapted to this variation. 
 It is sufficiently rigid to resist the influence of a moving load and 
 distribute it over 100 feet of the plutform, but is not t(X» rigid to 
 yield fairly to the necessary changes in the position of its centre. 
 
 Tlie platform is wonderfully stiftene«l by a light, yet strong 
 reticulated truss on either side, GJ feet deep, going down two feet 
 below the road, and rising 4 J feet above it, formuig at the same 
 time a strong })arapet for the protection of f<x)t passengers. 
 
 The floor beams are of pine, 13 i feet long, and 2J x 10 inches in 
 the middle, bolted together in paii-s, and suspended five feet 
 apart between centres, the tension bolts })assing down between 
 them. They are notched uj>on the lower chord of the truss, which 
 passes under them and are fastened to it by screw-bolts. The 
 floor is uiade of two courses of Norway pine, 1 J inch thick. Be 
 tween it and the floor beams there is a series of horizontal braces 
 acting with the floor to keep the bridge in line. 
 
 The upper chord is C x 7i inches, made of two pieces of pine 
 3x6 inches, covered with an oak cap 7xlJ inches, breaking 
 joints, and bolted together. Tension braces from the floor beams to 
 this chord serve to keep the truss in a vertical position. 
 
 The lower cliord is also made of pine 6x8 inches, in two pieces 
 of 3 X 8 inches, and under them a wrought-iron channel bar Ox k 
 inch, with flanges turned downwards two inches deep^ and weigh- 
 ing 30 lbs to the lineal yard. These channel bars extend all 
 across from shore to shore. The joints are fished with cr^vering 
 plates 15 X 5 X I inches, and eight screw bolts to each joint, the 
 
)mIm beiii^ Hlottt'd to iiiiuw r«tr tiic coiitractiun titid cxiiuitHioii iif 
 the iiictHl. TIiIh fuiiiu'cti<»ii of wroiiglit-imii uihUt tlio trii«M givt's* 
 it grout luMlfHuml Htitt'nesH, a?* well as toiHili* sfroiigtli, hihI pro- 
 veiitti tlie Htuys pulling the chonl usiiiMlcr. 
 
 To couiitcnu'ttho horizontnl tiiniHt oftlio ntays, the lower chonl 
 is graduull}' eiilurgocl from tin* point when' tlu- longest stay id 
 Hftached, toward lM»th towern. I'lom ♦» xS inclit'sat the iniddlejt 
 is IncreaHcd to H x 8 iiu'he^ at thisi ]>i>inr, and ono inch in added to 
 itH width at every CO feet until the lower «hord in enlari;ed to lli 
 X 8 inches at the landinj's. Abuttinj' blocks and transverse heaniH 
 of oak an; bolte<l to this jmrt <»f the chonl for the attachment of 
 the stays and jj^uys, and Ibrm, so t<» speak, a kind of stirnijt in 
 w hich the roadwav rests. 
 
 Between the top and bottom eliords of the truss is a series of 
 diagonal braces and vertical tension bolts, bindinj' the><e two 
 members firmly to<rether, tlin»n<j;h the oak cap and chamiel bar 
 at top and l)ottom. * 
 
 The cross braces are CxL'i inches, witli lonnded ends where 
 tlieyabnt against tlieoak prisms which an? hollowed out for their 
 reception, and by whicli the tniss accommodates itself to the rise 
 iaud fail (»f the roadwav without rackini; tiie framework. 
 
 At the middle of the bridge, the weight of the cables, which 
 here de.seen<l to tlie level of the ntadway, is brought t<» bear 
 directly upon it, an<l acts as an insistent weight to ju'cvent it 
 being liftetl by the wind. At the point <»f oscnlation of the two 
 reverse curves formed bv the cables and the n»a<lw;iv, the Hoor 
 beams are screw-bolted close up to the cables, and at every fiftv 
 feet ot the 200 feet each side of the centre, a stu«l <»r pillar made 
 of a two inch gas pipe, enclosing the susjiender, is placed 
 between the cable and the roadway. These studs serve to spread 
 the inertia of the cables over 400 feet of the central portion of 
 the bridge, combining it with the rigidity of the side truss to 
 give stiffness to the roadwav. 
 
 VIII. THK A.\( IIOKAOKS. 
 
 The anchors are of cast-iron 3i x 5 feet, weigliing uj»wards of a 
 ton each; pierced for the reception of the anchor bars, and 
 having deep flanges on the back against which they are secured 
 by steel pins. They are placed seventeen feet below the surface 
 of the ground. On the Canada side they are embedded in the 
 
-••lid liinoMtoiio riK-k which in liorizoiitally ntratitu'«l, aixl rcachcn 
 to witliiii one t(M)t of the Hiirtaco ^A' flio «^roui»(I. A chaiiiiol wjis 
 cut tliniiigh thiH r«K!k Jimt larji[c cjuui^h to rcocivo tlic anchor 
 chains, and at the oxtrcinity, or lower ond otthi« t'liannL'l,a cliain- 
 hjT was (>\('avato<l tor tluMinc lion*, and tlio jandw or shonidorM 
 against which thoyaro titted, wore accurately cut out of the native 
 nx'k, in a |>lane at ri^ht anj;lt»s with the direction of the anchor 
 chains. The sides and lower edges of the anchoix have thus a 
 tinu and even bearing a^jainst a stratinu of rock six feet in thick- 
 ness, and the top l»(»ars a^^ainst a large key -stone jdaced over the 
 chains which, as it were, l<K*ks and hars the chamber door. The 
 whole is built in with hv<lraulie inusonrv, and car(>fiillv irrouteil. 
 8u as perfectly to fill all cavities. 
 
 On the !Xew Vork side the anchors are similarly set in ii niait 
 of solid masoTirv, the course of the chains beinix lined throu<rhont 
 with heavv cut ashlar so as to form a solid tl(M>r and cover for the 
 chains, and bv means (»f bond stones and the adhesion of the 
 cement, to bind the whole mass together as one soli«l stone. 
 
 The bodvof masonrv in both anchorairt^s below the <rrountl line 
 
 on the New Vork side contains 530 cubic yards of masonrv, and 
 
 Vhen com[»lete(l by the two pedestals tt) be built above ground, 
 
 each of whis'h Mill be 80 feet long, seven feet wide, and seven feet 
 
 high, enclosing the ends of the cable; the anchorages on this side 
 
 will contain 080 cubic yards of masonrv, and the weiirht of it will 
 
 be 1415 tons net. Rut before the inertia of this mass can be 
 
 overcfune, an equal bulk of sand ami gravel surrounding it wf>uld 
 
 have to be moved, and the total resistance opposed to the 
 
 tlirect strain of the cables and stays will not be less than 2400 
 
 tons. 
 
 On the Canada side, the an(;hora have a linn hold of the solid 
 
 rock, and the resistance is incalculably greater. 
 
 The weight of the bridge, and its greatest load, 803 tons, will 
 
 j)roduce a maximum strain of 705 tons upon the cables and stays 
 
 but one-tenth of this strain is thrown down vertically on the 
 
 bearing stones where the cables enter the ground, by virtue of the 
 
 change of direction of that point. Hence the greatest pull upon 
 
 the anchors cannot exceed 684J tons, and as inis strain scarcely 
 
 exceeds one-fourth of the dead weight opposed to it, it is appa. 
 
 rent that the anchorages cannot be disturbed or in any way 
 
 afiected by the greatest tension of the cables and stays. 
 
. • 
 
 24 
 
 THE STREN'OTH OF THE BRIDGE. 
 
 The cables, as they hung freely between the towers, before 
 they were loaded with the roadway, formed u pure t*atenuriaii 
 curve, the properties of which are well known to the niatheniati. 
 cian; but when the roadway was added, which in any suspension 
 bridge is much, or many times greater than the weight of the 
 cables themselves, their primitive character was changed, and 
 under the influence of an equally distributed load they assumed 
 the form of a parabolic curve. 
 
 The difference between these two curves, in deducinjj: the 
 strength of the bridge, is inconsiderable, but in calculating the 
 lengths of the suspenders, and fixing the curve of the roadway, it 
 cannot be disregarded. The parabola gives the readiest means 
 of finding them, and the lines it furnishes approximate more 
 nearly to the curve of equilibrium. A foreshortened view of the 
 br'.dge, as seen from either bank, brings out the harmony of these 
 lines in a very ogreeable manner. 
 
 THE CABLES. 
 
 A y 
 
 1 
 
 D 
 
 I 
 
 \ 
 
 
 / 
 
 
 c 
 
 X 
 
 ^y 
 
 • 
 
 To find the length of the arc A C B considered as a parabolic 
 curve : 
 
 Let *S' = J. 6' = half the arc. 
 y == AD'= half the span. 
 X ^=M J) C = the depression of cables at centre. 
 
 y^^m^^ry^ y + ^4:?n* + y'' 
 
 Theii accurately, S =^ + m. log. — —- 
 
 4 7?i € 2 m 
 
 The symbol log. standing for the hyperbolic logarithm. 
 By the equation to the parabola : 
 2/5=-= 4: m X, 
 
 . and — — 4 ?7i — the parameter. 
 
 X 
 
 The vertical deflection of the cables at medium teinjjerature is 
 91 feet, consequently the swayed cables have an incline<l deflec- 
 tion of 92.22 feet, and the length of the arc must be measured 
 by this. 
 
25 
 
 Substituting tlio values of x and y in the foregoing e<iuation : 
 i. e.— J? = 92.22 
 y = 634.17 
 wo find that half the arc S =- 643. and 2 S, the whole arc 
 
 ^ 6' j5 - 1286 feet exactly - - - - (1.) 
 Similarly, if the detiection be taken at 90 feet vertical, the 
 Fwaycd deflection becomes 91.24 feet and the length of arc 
 
 A a B -^ 1285.62 feet exactly. 
 For a deflection of 92.22 feet the arc measures exactly 1286.00 ft. 
 For a deflection of 91.24 " it is 1285.62 " 
 
 Differences 0.98 0.38 
 
 Hence the increment of 0-38 in the arc, gives an increment of 
 0.98 to the deflection, and their ultimate ratio is as 38:98 (2) 
 ^ The greatest tension upon the cables is at the j^oints of suspen- 
 sion A and B. 
 
 Let y = half the span =- 634.17 i^Qi^ 
 ^ a? =. the vertical deflection = 91 feet, 
 
 r = total weight of the bridge, and its load e([ually distrib- 
 uted, 
 T = greatest tension upon the cables,re8ulting from the loa<i /*, 
 Then the curve of the cables being considered as a parabola 
 
 4aj 
 
 And by substitution 
 
 P 
 
 r= v/634.ir+4x9r 
 
 4x91 
 
 = 1.81 P (3.) 
 
 That isj the factor 1.81, multiplied into the load P, equally 
 
 distributed, gives the strain upon the cables at the point A. In 
 
 other words, every ton laid upon the platform ])roduces a 
 
 strain of 1.81 tons in the line of the cables. 
 
 THE STRENGTH OF THE STAYS. 
 
 If ^be the angle of inclination of the stays, t.^,, the angle 
 ^jE'-F at which they intersect the horizontal plane, then their 
 effect in sustaining a given load varies as Sim,. E — the smaller 
 the angle the less their effect in giving vertical support. But to 
 compensate for this difference, tlie strength of the stays increases 
 
86 
 
 .in the inverse ratio. Three sizes of ropes are used, the longest 
 being nearly three times the strengtii of the smallest. The angles 
 vary from 16 to fiTi degrees. 
 
 As they are a])pliod every one (»f the 48 stays is found by the 
 resolution ol' forces to possess a lifting pfjwer varying from nine 
 to fourteen tons, or from two to three tons effective strength. 
 
 The aggregate strain on all the stays is exhibited in the repre- 
 sentative triangle of forces B E F (see the figure) deduced from 
 the plans. The sum of all the breaking strains being represented 
 by the line B E -^ 1,344 net tons, tlie sum of the horizontal 
 thrusts against the abutments will be represented by the lino EF 
 =1,148.67 tons, and tlie aggregate lifting power of all the ropes 
 will be represented by the line B F -^ 628.54 tons. 
 
 The same proportions hold good for all otlier strains less than 
 the breaking strain. If B F =^ 1, then B E— 2.14, and EF 
 =1.83. Let B E represent the entire weight ( /*) to be su]iported ; 
 then the strain upon B ^will be 2.14 P^ or 
 The average strain upon the stays = 2.14 P - - (4) 
 
 T'ue bridge is supported by cables and stays. Tak- 
 ing these separately, the cables have to su[)poi-t, 
 
 1. Their own weight. Bv (1) '^"^^^^ -= 81 tons net 
 
 2. The weight of 634 feet of the central portion ^^\. 
 the bridge, including all the suspenders, the cable 
 bands, tension bolts and washers, over the whole 
 
 length - - - ^ - 70.60 " 
 
 3. The w eight of the imderfloor guys attached to 
 the central part of the bridge, including a quar- 
 ter of a ton strain on each guy to keep it taught 5.00 " 
 
 4. The weight of the bridle and horizontal stiys be- 
 tween the cables, including a quarter of a ton 
 
 strain on former ----- 2.00 " 
 
 Total weight resting on the cable, net tons =167.60 tons 
 The strain upon the cable produced by this weight 
 
 is, 
 By (3) 167.60 x 1.81 = 303.35 tons - - (5) 
 
 The stays have to support, 
 
 1. Their own weight and attachments - - 18.00 " 
 
27 
 
 2. The weiglit of the two Uwidward quarters of the 
 platform equal to one-half the roadway, minus 
 
 the parts resting on tlie rock — say 556 feet in all 85.00 " 
 
 3. The weight <»f the guys attached to this portion, 
 and a quarter of the strain on each of the inclined 
 
 guys - - - - - - 12.40 « 
 
 Total weight resting (»n the stays - -95.40 " 
 
 The strain produced by this load is, 
 
 . ]3y (4) 05.4 x 2.14 =-= 204.15 tons - ' - - (6) 
 
 I 
 
 I The calculated strengtli of the cables has been thus deierniined. 
 
 I Tlie manufacture' r's rule for ascertaining the strength of the 
 
 best quality of wire rope licretofore made is as follows : 
 
 If W ==^ weight per fathom of the rope in pounds, 
 
 i£ =-= its breakijig weight in gross tons, 
 Tlien, makinjnr all due allowance for the lav, 
 
 I Tliis rope weighs 54 lbs per fatliom, and its breaking weight 
 I' B ---'Ix 54 — - lOS gross tons, -= 120.9G net tons. 
 
 There is good reason, however, to know, trom the superior qua- 
 lity of the material used in their fabrication, that the strength of 
 these ropes is even greater than this. The wire was drawn to a 
 specified tension f>f 100,000 lbs on the scpiare inch, and the regis- 
 try of tests proves tiiat on the whole they greatly exceeded that 
 limit. While the rf>pe3 were being made at Gateshead, I wit- 
 nessed the breaking of one of the wires by direct weights and 
 lever power. Tlie guage was .154 inch. The weight per fathom 
 .376 lbs, per yard .188 lb.- It broke with a weight of 1,920 lbs. 
 Since a bar of wrought-iron, one yard long and one inch square, 
 weighs ten pounds, we haye -1'^ = 53.2 wires of this size to the 
 square inch, and the strength of the wire is 
 
 53.2 X 1,920 = 102,144 lbs per sipuire inch. 
 
 The strength of the rope by this single test is therefore 
 133 X 1,920 =- 255,360 lbs — 127.660 tons. 
 
 Deducting 5 per cent, tor rope making — 6.384 " 
 
 B =. 121.295 " 
 It is fairly within bounds to assume that the breaking strain is 
 121 tons, an<l consequently the strength of the two cables is 
 
 121x14 = 1,694 tons net. 
 
28 
 
 By tlio same rule the strength of tlie stays, at the lowest esti- 
 mation, is as follows : 
 
 12 stays, 4i incli circ.,20ll)s per fiith., 40 tons B.S. — 480 gross tons 
 24 « 3i " 11 " 22 " -= 528 '^ 
 
 12 " 3 " 8 " 16 « ^ 192 " 
 
 48 stays have an aggregate breaking strength of 1,200 " 
 
 Equal to 1,344 net tons. 
 By (5) the permanent load exerts a strain on the cables of -^ 
 ])arts, between one-fifth atul one-sixth their breaking strain. 
 
 By (6) the permanent load on the stays exerts a strain of -^ 
 parts, between one-sixth and one-seventh of their breaking strain. 
 And taken 
 
 Collectively, on Cables, on Stays, 
 
 Tlie permanent loads are 167.60 tons x 95.40 tons, = 263 tons 
 The resulting strains are 303.35 " x 204.15 « = 507J " 
 The breaking strains are 1,694. " x 1344. " = 3038 " 
 
 Hence, the entire weight of the bridge, 263 tons, produces a 
 strain in the line of the ropes forming cables and stays of 507 i 
 tons, which is as nearly as possible one-sixth their breaking 
 strength of 3038 tons — equal to 20 tons on each rope ot 121 tons 
 strengtli. This leaves a safe margin for tlie effects of tlie wind, 
 the moving loads, and sudden accumulations of ice and snow. 
 
 Tlie bridge liaving been designed for light traffic, and 
 intended to be used under special regulations in regard to the 
 loads to be admitted on it, as provided in the Act of incorpora- 
 tion, it may be considered safe if the permanent load does not ex- 
 ceed nne-ffth^ and the pennanent and transit<.>ry loads taken to- 
 gether do not exceed one-fourth the breaking weight. 
 
 Let /* = the weight of the bridge = the permanent load. 
 L = the greatest load admissable upon it. 
 T =- the factor of tension in cables and stays produced by 
 
 the permanent and transitory loads P and Z. 
 B = breaking weights of cables and stays. 
 
 Then allowing a strain of 25 per cent of the breaking strains, 
 the greatest load : 
 
 B 
 
 Z" r 
 
 4 T 
 
29 
 
 By snhstitution for cables: 
 
 1694 
 
 Z -=, 107.60 ^ 66.37 tons. 
 
 4 X 1.81 
 
 and by substitution for stays : 
 
 1344 
 
 Z 95.40— 61.37 tons. 
 
 4 X 2.14 
 
 max. load on bridge - - 127.74 net tons. . 
 
 While tlieretbre a load of 127.74 tons equally distributed, 
 would not strain the ropes more than 25 i)er cent of their full 
 strength, there can be no doubt of their sufficiency to sustain 
 safely the load of one hundred tons, for which the bridge was 
 designed. In point of fact, in the course of construction, the 
 cables were put to a test which is er|uivalent to this load. 
 Betbre any of the stays, which carry one-half the load were 
 stretched, before they relieved the cables of any part of it, 
 the cables alone sustained tor some weeks during the storms 
 ot autumn nearly the whole weight of the bridge. The dead 
 w^eight they bore at such disadvantage, including their own, 
 was 211 tons. Their deflection at that time being 88.80 feet, 
 the strain produced by this load was 391 tons, equal to 28 x 
 
 tons upon each rope, the same as that of the maximum load \ 
 
 of 100 tons. In this way, therefore, the cables have already 
 been tested to the full strain of the maximum load. 
 
 THE EFFECTS OF TEMPERATURE. 
 
 It is assumed that under the modifying influence of the Falls, 
 the greatest cold will not be below zero of Fahrenheit, and the 
 greatest heat will not exceed 100 degrees by the same scale. The 
 range of temperature provided tor in the adjustment of the levels 
 and the construction of the roadway was 100*^ Fah't. 
 
 The length of the cables exposed to atmospheric changes is 
 1800 ft. It is known by exjjeriments that wrought iron expands 
 .0012 parts of its length between the freezing and the boiling 
 points of water, that is, between 32? and 212'^, equal to a range 
 of 180 degrees. 
 
 The expansion ot the cables for 100° range of temperature is 
 therefore ||g x 1800 x .0012= 1.20 feet in the whole length. 
 
 By (2) .38 : .98 : : 1.20 : 3.09. 
 
 
30 
 
 Tliftt is, tlie increase (»i' 1.20 jti tlie lengtli of tlie rabies will 
 produce an increase in the dofkction (.f'.S.OO t'oet, wliicli is the rise 
 and fall of the bridge due to changes of temperature alone. 
 
 THE KFFKCrS OF THK WIND. 
 
 It would seem as if every wind that blows rusjios into the 
 chasm crossed by this bridge with re(lonbl<.»d force. Winds that 
 are but gentle breezes on the land strike the bridge with the force 
 of a brisk gale, and a gale on land becomes a storm on the water. 
 They press through the gorge as through a funnel, with increased 
 velocity and power. Even in calm weather ]»nlfs of wind come 
 lip from the mysterious depths of the P^dls as from the cave of 
 ^olus, surcharged with spray, and then there may be seen, in 
 sunshine, the new plienomenon ot a rainbow both over and un<lcr 
 the platform, describing a complete circle round about the bridge. 
 
 The bridge is undisturbed by ordinary whids, but in the course 
 of construction there were severe storms that ail'octed it to a con- 
 siderable extent, until all tiie stays and guys were attached and 
 brought to bear upon it. By these and by the cradle form of the 
 bridge, the lateral force of the wind, tending to produce oscilla- 
 tions, is at once resisted and checkeil. The undulations from the 
 upward pressure of the wind, and from transitory loads, are also 
 checked by stays and guys as far as they reac^h, and beyond this, 
 over the remaining space of 400 feet at the middle, it is counter- 
 acted by the vertical studs placed between the cables and the 
 roadway, as before stated. 
 
 The prevailing winds are from the south-west. Coming from 
 the open water of Lake Erie, they are like^^ ise the strongest, and 
 striking the bridge square upon its beam, act with nnich more 
 power than any other. Allowing for a great storm, greater than 
 any yet experienced in this locality, and next thing to a hurri- 
 cane, and that it strikes fairly on one side, it will press with a 
 force of 30 pounds upon the square foot, and exert a lateral 
 power of 108 tons upon the whole length of the bridge. But the 
 wind passing under the bridge has always an upward tendency. 
 Then if the angle of incidence be taken at 45 degrees, its greatest 
 effect, we find that while the lateral force on the side is reduced 
 to 68 tons (as 1 to /Sin. 45 deg.), it is also increased by the hori- 
 zontal resultant of the pressure on the bottom by 140 tons, and 
 
31 
 
 hence the greatest hitcrul pressure will be 208 tons. To resist 
 this tlistiirhiiiij force we have : 
 
 1. The inherent stittness of tlie plattorni, lixetl at both ends to 
 the solid rock, and fastened at the niid<lle to cables Weighing 81 
 tons. 
 
 t 2. The cradle form of the bridge, the cable and stays bein"* in- 
 clined at an angle to resist any lateral motion. 
 
 3. The weight of the entire suspended system, 2C3 tons. 
 
 4. The direct [)Ower of the guys, their united strength on 
 each side being 280 and 2C0 tons respectively. 
 
 Tlie ui)ward j)ressure at the same angle of incidence will 
 likewise be 208 tons. The platform, with the guys attached 
 to it, weighs 15G tons, or 58 tons less than the lifting power 
 of the wind; but the united strength of all the guys that hold 
 it down is 460 tons, and the central half of the cables also 
 presses upon it through the studs with a dead weight of forty 
 tons. 
 
 I have now laid before your board a full and particular ac- 
 count of the bridge, exhibiting its strength and construction. 
 To complete the design, there yet remain the following works, 
 whicli can be proceeded with next Smrmier : The building of 
 the four masonry pedestals for enclosing and protecting the 
 anchorages; the covering in of the towers; the painting of the 
 iron and wood work; the permanent seizing of the stays to the 
 suspenders; the finishing of the approaches, and the division 
 of the roadway by means f angle irons; the addition of one 
 more stay and a few moie guys, and a few other things of 
 minor importance. 
 
 Before concluding, I have to thank the Directors for tlie very 
 complimentary, and to me very gratifying resolution of the 
 Board, passed unanimously at their last meeting of the lltli 
 ult, a copy of which has been forwarded to me, expressing 
 their entire satisfaction w ith the mamier in which I have car- 
 ried out the important work committed to my charge. I must 
 also express to these gentlemen' my grateful acknowledgments 
 
32 
 
 for the confidence tliey invariably placed in mo ih their En- 
 gineer from the time I first entered their service. 
 I remain, 
 
 Gentlemen, 
 
 Yonr obedient Servant, 
 
 SAMUEL KEEPER, 
 
 Engineer^ 
 Clifton Suspension Bridge, Niagara Falls. 
 Brockville, Ist March, 1869. 
 
33 
 [Copy.] 
 
 Tn thP PllKMDENT AXI> DiRKCTORS O/* t/lC XlAC.ARA FaLLS SUAPENSIOK 
 
 Bridge Companv, and tn the President and Directors o^<^ 
 Clifton S('!*rEN;*K>N' Briikje CoMPANr: 
 
 Gentlemen — 
 
 Your bridge Ininj^ now ready to ^i)e opened for public travel, 
 and completed in all particulars, except a few comparatively unim- 
 portant oncH, I avail myself of this occasion to report to you in 
 writing the results of my connection with the undertaking as Con- 
 sulting Engineer. 
 
 In May last your chief Engineer, ^Ir. Samuel Keefer, invited 
 me to examine the plans which he had pre))ared for the work, and 
 I spent a week in carefully revising his calculations of the strains, 
 and of the dimensions to meet those strains, and in the examina- 
 tion of the cables and ropes which had been prepared, and of the 
 towers, then nearly completed. 
 
 At this time I expressed to you verbally the following opinion: 
 That the plans had been prepared in the most complete manner, 
 including the most minute details, and that they had been ar- 
 ranged of the most ample strength in every part to sustain the 
 greatest load or strain to which they would be piubjected undei 
 any circumstances, and four times as great as that which the 
 heaviest contemplated load would impose. 
 
 I also found that the arrangement of the whole structure, and 
 of its various parts, had been admirably adjusted so as to produce 
 the desired strength with no unnecessary outlay. 
 
 The cables and ropes, which had been purchased by Mr. Keefer 
 in England, from R. S. Newall <fe Co., were most beautiful speci- 
 mens, and having been tested at Liverpool by the Government 
 test, were of course perfectly reliable. 
 
 The anchorage was arranged admirably, so as to give to this 
 important part of the work an extra degree of strength and secur- 
 ity. 
 
 I also found that the towers had been made abundantly strong, 
 and were arranged for stability and durability. 
 
 On my second and third visits in November, I found that the 
 main portions of the works were nearly completed, substantially 
 upon the original plan. At that vi :lt I saw what must be regard- 
 ed as a complete test of the cables. Nearly the whole weight of 
 the structure was at this time sustained by them alone, without 
 the aid of the stays (which now carry one-half of the load), and 
 
 / 
 
34 
 
 only a few temporary guys, and the stnicturu subjcctt'd, in thin 
 imperfect condition, to the Bcvcre acti(m of very high windw. 
 Such a test in twice an Hcvere as any Kngincer would venture to 
 subject the bridge to on a trial of itn strength. During my pre- 
 sent visit I have witnessed the etfe<t «»f a territlc gale; and these 
 examinations of the plans, and observations of the bridge itself, 
 assure mo of the correctness of the opinions ol the strength of 
 each part of the structure wIh-u cninplcted (ns it is now almost) as 
 perfectly ample for safety under even extiaordiuiiry circumstances. 
 To Mr. Keefer is due the highest meed of praise for the |»erfec- 
 tion of his phins for the hirgest-spanncd bridge in the world, and 
 for the rapid and ecomtmic manner in which it has been executed. 
 It alone would place Mr. Keefer among the highest in rank in the 
 profeubion. 
 
 I am, very respectfully yours, 
 
 (Signed) ^\. .1. MrAlJMNK, 
 
 J 
 
 Niagara Falls, X. Y., '25th Jan., IHOU. 
 
 tsfnm rriillBC Co., '4 ImI Bwui Si, Bmfiilo