Show RON crystallization how it irilua ultan ax in till fiber ot tile 1141 A anil annl weakens it ft since a pa cai or train wi on tile the north britis Brit ih railway eting plunged ed front from the great bridge bride over the firth fit of tay into the alie dark below one stormy december ber night I 1 seven evcic acar i ago t cArr carrying YiT every evi livin living soul au upon it to certain death there has been no railroad rail roid I 1 bridge bride brid e disaster that lias has excited so ciuch public attention ns s that which occurred on the boston boiton railroad it at tile the bussey brid bridge c it ear bost oil in hatli alio canse appah i to have been a defect this may also ile be said of t alie IL t whose horrors however were i increased by the fierce work of lamps and the of a bitterly cold winter night bridge accidents are considered by all railroad men mail us as incomparably ly the worst to which travel by rail cail is exposed and aa is amon among t alio lie must most difficult to guard air against a dinst absolutely one source of danaher ww was shown when tile peculiar effects of a 1 lo locomotives colnot ires harr hammer inter blows upon a track were explained tho the theory was advanced that a girder arder of the bridge had broken beneath the engines drivers whose poun pounding dince C upon t alie te defectively constructed bridge was vas thus primarily the cause of ill the accident co this brings up tip a phase of railroad and bridge accidents which is at I 1 present receiving e a great deal of atten I 1 i tion crystallization lit in the material of iron iron brid bridges brides es is an element clement of danger M now so well reco recognized nihed that the penni sylvania railroad company lias adopted the definite policy of substituting stone for iron brid bridges brides es and the same plan is being followed by other r railroad companies the lifetime of an iron bridge 0 is from twenty to twenty five years years and constant stant care is necessary to insure its I 1 safety the ashtabula briar bridge c was I 1 thirteen years ears old and at the time I 1 it I 1 fell beneath the weight of two ell engines ines and a lie a v y express train the theory was commonly advanced that crystal leation izi tion had bad impaired its oric original rial strength the two t great moving 0 causes canses of crystallization are vibration and tire the hammer blows of tile the locomotive re which gradually by repeated impact turn the fiber of iron or steel into a mass of crystals needing only some unusual pressure or blow to cause them to break apart add to this the oscillation caused by the passage C of trains at a 1 high rate of speed sliced and I 1 it will be seen that an iron bridge 0 is exposed to peculiar perils which can only be guarded against by rima rigid inspection and con stant slant renewals cras crystallization tall i aaion was one of il theories advanced by pirk park benjamin a new york engineers engi neero account for the tny Tay bridge accident lie daiil general genei ail indications go to show that the cause must lie a sought r in an abnormal condition of the structure or rather one which did not enter into the calculations of the builders builder such a condition would be the deterioration of the metal by its alian change e from a fibrous to a state under repeated vibration that this occurs lit in rail ivay brid bridges t has been vigorously disputed by many well known engineers k anthe on the other hand many examples are quoted by different diu crent authorities to support the theory apropos 1 to this particular accident a distinguished a french en engineer and iron founder found er now in UL country informs us that lie has known bars of iro iron it made by himself from scotch pig to efroin a tough lough fibrous to a brittle crystalline structure in traveling by rail only f from rom tile the north of france to this is of course an extreme instance A again ain recent research lias has demonstrated that because a i structure withstands a lar large c quiescent load that faath act is little proof of stability under ul ider re heated shocks alid vibrations metal art are believed to toli have area a life A bar foi example may stand a million vibrations and break down at tile the million and first and yet the last shock may be bc lighter C than preceding I 1 ones attempts attempt S however to reduce this law t tc practical lical almli application cation have elicited an abundance of conflicting evidence but nevertheless it is well settled that tit it lit in no department of mechanics ine chani es h 13 an extended course of actual ex experimenting in more urgently 0 needed or of waver graver r public importance the strength th of ilia hie tay bridge tit at the time of its A 3 building was such that it was aas pronounced perhaps tile the most remarkable structure in the world 19 engineering a british ilia magazine I 1 aai no speaking in r of its itis test when five engines weighing tons were placed ona on a single span said the result is tile tho complete establishment of this fact so important to the public t eliat at tile bridge brider e is strong m out of all pi proportion op to its p possible biec necessities essi ties the load which the structure is calculated to carry is six times greater than that to which it was and yet th great bridge which cost 1 ail lapsed within a few months aft 1 it was finished the accident being ye a only one in all railroad aich no survivor lived to tell the tale ceol the t of crystallization put for ward at I 1 tace le time of the ashtabula Ash tabala bri bridge d ge diar dis dimpter Pter ater is now accepted as aa ic ac counting n I 1 ir r many rat railroad accidents and seems I 1 peculiarly applicable to the fail of tile bussey bridge e vibrations and liamin liam nii r blows would seem to have crystallize crystal bizet some portion of chest alic rue alre re and p spared it for fora a fall when at last tile li a of a girder had been beell ex cx Im liau stud a an d it bro broke ke beneath tit tin 0 ellit ellinos I 1 inos s t dmn 1 pi ping IT driving arlvin wheels wheals kiil adelphia ti JI eford ord |