Show Y AKIN LETTER or t the iO smas u ua used ma lOa may cause the tho failure of tho the structure ol In involving the loss of millions of dollars anti and much human life When the tho first Quebec bridge c was as about half completed in 1007 it c collapsed without without with with- th out warning Ei Eighty persons were Killed and a n vast amount of monc money lost Tho failure wa was duo to faulty ma materials tennis It was De to o sustain a unit weight of pounds pound and antI failed u under tiller a stress of lc less than 1 1700 1 In Inthe Inthe n the tho new structure c every possible pic- pic rc- rc caution is taken to guar guard against a repetition tion of the tJ disaster Every Li bit bitof bitof t of material is subjected to tho the most ri rigid id te tests ts and the expert brid bridge c builders build ers ors of the tho continent tiro aro ea eager cr to ins inspect oct the methods metho t b by which this is being done ono in the various arious parts of ot tho structure The rho trusses of tho new bridge are arc to be twice as strong and the bottom cords five fire times as strong as the tho first bri bridge 1 e This bridge is to be located about ci eight ht miles from Quebec and will contain tho the largest single span of an any brid bridge o yet built the distance between the two main piers bein being 1500 feet Design Is Remarkable It is not so much for its size size how however ever over as for its design that the Quebec bridge is remarkable Several eral brid bridges cs in the United States are arc larger and rind have cost more to erect Amon Among them themis is ts the Manhattan bridge in New 1 York rk I City recently opened for foot foo c j I This bri bridge o is a a. pattern It Its fir first t d deck ck will have a thirty five s foot roadway in the center and aud two subway tracks and an eleven foot wi wide e foot walk upon each side ide The Tho top deck will have hac four trolley tracks s. s The Thc total width of the Manhattan brid bridge e is 10 feet The rho land lanel secured for its building b included ct feet upon each water ater side Tho The land upon the Man fau Manhattan hattan battan side Elide cost It Tt was in the improved tenement district and antI it was nas necessary to condemn man ninny many bu buildings 8 which hero paying pain their owners own Or Ors ers good tood profits The Brooklyn land Janel was in a poorer district and only half as valuable The Tho development of railroad traffic has bas had a great influence upon the methods and requirements of bridge c construction Both cars and antI locomotives tives ti arc being built heavier than formerly for for- merly in order that the they may carr carry seater greater eater Joad loads The stress upon tho the railroad brid bridges cs has bas increased proper Upon some roads all fright ht cars aro arc required to have ha a capacity of l pounds An n important feature l' l tute or of railroad bridge construction is strengthening a bridge or replacing it with a new one without interfering with traffic Sometimes this is done one b by substituting false falso work under the b bridge while hile new supports arc are being bein- built Sometimes other means are used Make Notable Changes A bridge cro crossing sing the Iowa Towa river er at Columbus Columbu junction has lias been ODe one of ot the recent notable reconstructions Sometimes Some orne times it becomes necessary to have ha a double track in place of a 2 single ono cue A bridge near Montreal has recently been changed front from ron rona a single to a dou dou- his track without interfering with the traffic Another track was built next i to the old on ono The old bridge o was waa then removed remo span sian by bJ span so IO carefully that parts of it could bo be used else else- where Then a n F second cond new lIew track was built onto thu tho first thereby making a complete double track bridge g The Tho improvement in metal rn tures has given a greater tensile I strength to steel and aud made possible I feats which would not have been undertaken un un- a H f b few w years cars ago ngo While some Homo concrete bridges aro are being erected steel is iN now the most important bridge o building material The first metal bridges were cre of cast cad iron ron und surd they tho I came ennio into use me near the clo o o of bu the ei eighteenth century The first of If f these e I Iwuc wat over the Severn e ern rn T river cr in iii and the most celebrated the tho bridge e erected over o the lie Thames river which whit was opened in 1821 Cast iron was superseded dell by hy wrought ht iron ii iu iii construction The Thc bridge on tubular bridges of or tho the type trl c of ur the tho Britannia bridge e ns in En England I and ami the till Victoria ictoria riI bridge in Montreal ar the bet best exam xam I pies of wrought iron bridges bridge No im im- important structures of the kind were built bum in the United States The iron girder bridge the cantilever r bridge brids and the thel suspension bridge rid c are aro the three typos types now most popular Many noteworthy examples of each have 0 hem ben erected d in this country in tn inthe the tbt past pact quarter of a century Tb The bridge crossing the J Jn n t II k river r r upon t the le Cincinnati Southern rn railroad f in is II one e of tf the best long Ions span pan rr iron rou clr- clr L I r. r dor lor bridges el Th The framework i is 1135 feet Jon long and Consists on o of three It crosses crolle a B limestone canyon SO so feet above aboc the bed of the stream The I piers are nrc of at stone done for or sixty feet t with iron nl above l' l Adopt Foreign Method l The Tho cantilever cr design n i is fr from m the old oM Japanese method of i lots J lo s tO together in bridge o The rho modern c cantilever cr brid bridge bridges t is s a I succession of iron fron bracket each ach b arm composed of H a rigi rigid j The Forth bridge 0 of Scotland Scot Scot- I land and considered until unlit recently tho the finest in t br bridge tl o in ill tho the world orM ia is tt a i T T n pi passage of ff vessels e sol Tho The Tho larg largest sl ere eVa lent leat bascule ee bridle bridge in the world H been completed in South C Ci Cage It crosses lS the trio Calumet Cal ri The Tho length lh of the tho movable ahle span is ia feet ct and it Veil weighs 1300 fon Ions IM I'M whole mass can u he bo moved ocd b by Ity s ani ani an i in a minute and a n quarter s vm no more exertion than starting t c trolley ear car It is or cl electricity t lust but a gasoline a. a en cn cos driver r is is 19 provided tar for A lifting Meek deck of the Inn bridge gives fi i cs a n clearage of fifty lifty f feet for the steamboats tl y Ui i tho the Missouri r river cr I Need Deeper Foundations Foundation Tho rho increased strain upon ullon bird hr caused by hy the heavier ier loads p pi i over or them calls for deeper than formerly This Thia requires Jari la and deeper excavations lh These c only be bo accomplished b by tho the si of caissons into the ground far under the level lovel of oC tho the river Tho The water is is pumped out of i t t. t caissons and the men nice make the ca being supplied with air tubes going down from tho surf Working under such conditions lit hazardous as well as ns men mental l to the tho health and aud it is el i that thousands of or men nieu have ha died f it Caisson disease may be bo fatal it fr frequently brings s 9 about parti t total tal 11 paralysis Caisson workers usually sent scat down iu Jil two hour few men meD being bing able to stag tan pressure for fora a longer period al ali i improved cd methods are continua Bening the difficulties of this this Most of tho the great groat modern brid upon caisson foundations These Then been made mado of timber iron iroD and aDd L Land and lately reinforced concerto has bar used In building the bridge e L tho the Niagara river at Black Rock Kock crete crote caissons were sent through feet of tough red clay olav to rock bo boThe bet bot The Key Ivey West railway extend one of the tho most remarkable b hr br building feats of the Ita day It It- It COB Oll oa the islands between the tho main mainline all FJ Florida and Key ey West by a n chair b r bw bridges bridge's es making possible a t co coati track for a distance of 18 V note noto worth worthy example of tho speed which modern bridge building 0 o Hans are carried on was given at island Now Jersey last summer K two and a half n miles i os of trestle br bt which had been destroyed b by fire replaced in iu twelve days This o tion employed a force of 1 1500 00 1000 of at whom worked on the daland dat dal and at It nj night V y ye |